Re: [time-nuts] Linear voltage regulator hints...
Dan wrote: My gut feeling is you are right about the GPS time base being sensitive. It would be fun to hack into this and try clocking it off the OCXO, but I'm not there yet! :) One interesting way would be to use the disciplined OCXO output to drive a DDS synthesizer set to the GPS unit's clock frequency (which, I'm assuming, is not the same as the OCXO frequency). This approach has a number of potentially large problems (delay, spurs, DDS resolution, to name just 3), so I'm doubtful that it would work well -- but I do think it's worth trying, just because it's so simple and cheap ($3.85 ebay DDS board) and potentially instructive. I might try some good old 'overkill' and put the GPS in it's own heavy aluminum box. It's been a thought for a while, and should address the thermal integration and time constants you referred to. Insulate the GPS card from the box (use nylon or teflon standoffs with no through metal screws), and insulate the box from anything solid (same way); i.e., only air can change the box temperature, and only air can change the GPS card temperature. Signals and power should go through bulkhead connectors and feedthrough caps on the box walls, with pigtails to get from there to the GPS card. You probably don't need anything too massive, just whatever cast Hammond box it will fit in (allow for the connectors and feedthrough caps!!). You can always add mass later (bolt slabs of aluminum to the outside of the box) -- but in this application, you shouldn't need to. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Yeah, I guess it's all relative. :) I do agree it is a HUGE change compared to what the GPS should see in normal operation. The same blast of air can be pointed at the GPSDO board for 20 seconds and see no change. On high at the oscillator for 60+ seconds with no change is apparent. The GPS is what responds. Does this mean anthing? It's well beyond what the GPS should see, so I doubt it. Is the GPS the most sensitive part in the system right now? Maybe. But, Bob could be correct that the OCXO is the sensitive part. The PWM DAC used to respond like the GPS to temp changes. Using 'heat and watch' found it. Addressing it has cut overall temp sensitivity down by more than a factor of 10. I consider that a measurable change. Any temp sensitivity left is really small, and wonder if it can be addressed with the hardware and tools at hand. My gut feeling is you are right about the GPS time base being sensitive. It would be fun to hack into this and try clocking it off the OCXO, but I'm not there yet! :) I might try some good old 'overkill' and put the GPS in it's own heavy aluminum box. It's been a thought for a while, and should address the thermal integration and time constants you referred to. For this system, it's doubtful that an underground bomb proof bunker is needed. ;) I'd like to learn more about what testing could be done and would be more than happy to discuss this off line, if anyone is interested. This thread has probably out lived it's useful life. Thanks, Dan LOL. A couple of seconds of warm air at 15C above ambient is a HUGE temperature transient for any sensitive electronics, especially anything with an oscillator. I would venture a guess that the lion's share of the drift you see is the GPS time base shooting off-frequency, but there are probably other effects, too (voltage regulators, to name just one). To me, a little change in this context might be blowing one warm breath toward the GPS unit from 18 away and seeing what happens over the next minute or two. But the GPS temperature sensitivity shouldn't be a big factor in actual use. The GPS should be thermally isolated from anything that changes temperature rapidly, and enclosed such that external temperature changes are integrated over at least tens of minutes. Then, the inside of the enclosure will reach its own thermal equilibrium and any external changes will be slowed enough to be tracked out by the GPS discipline. My recommendation would be to put it in a cast aluminum box (search the archives for cast aluminum box), but there are others who think you need to build a two foot cube out of cinderblocks and fire brick against a wall in the deepest external corner of your basement. OR, if my suspicion is correct that the temperature sensitivity is mostly the GPS time base, figure out a way to kludge the GPS to accept the disciplined OCXO as its time base. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi What you actually have tested (in this case) is temperature rate of change. The parts involved are designed for a rate change in the 0.1 to 1C / minute range. Taking them way outside that range leads to unpredictable results. In the case of the GPS, it goes into some sort of failure mode. It’s no different that taking an IC that’s rated to 125C and seeing what happens at 300C. That’s outside it’s design range and odd things will happen. Bob On Dec 14, 2014, at 3:38 PM, d...@irtelemetrics.com wrote: Yeah, I guess it's all relative. :) I do agree it is a HUGE change compared to what the GPS should see in normal operation. The same blast of air can be pointed at the GPSDO board for 20 seconds and see no change. On high at the oscillator for 60+ seconds with no change is apparent. The GPS is what responds. Does this mean anthing? It's well beyond what the GPS should see, so I doubt it. Is the GPS the most sensitive part in the system right now? Maybe. But, Bob could be correct that the OCXO is the sensitive part. The PWM DAC used to respond like the GPS to temp changes. Using 'heat and watch' found it. Addressing it has cut overall temp sensitivity down by more than a factor of 10. I consider that a measurable change. Any temp sensitivity left is really small, and wonder if it can be addressed with the hardware and tools at hand. My gut feeling is you are right about the GPS time base being sensitive. It would be fun to hack into this and try clocking it off the OCXO, but I'm not there yet! :) I might try some good old 'overkill' and put the GPS in it's own heavy aluminum box. It's been a thought for a while, and should address the thermal integration and time constants you referred to. For this system, it's doubtful that an underground bomb proof bunker is needed. ;) I'd like to learn more about what testing could be done and would be more than happy to discuss this off line, if anyone is interested. This thread has probably out lived it's useful life. Thanks, Dan LOL. A couple of seconds of warm air at 15C above ambient is a HUGE temperature transient for any sensitive electronics, especially anything with an oscillator. I would venture a guess that the lion's share of the drift you see is the GPS time base shooting off-frequency, but there are probably other effects, too (voltage regulators, to name just one). To me, a little change in this context might be blowing one warm breath toward the GPS unit from 18 away and seeing what happens over the next minute or two. But the GPS temperature sensitivity shouldn't be a big factor in actual use. The GPS should be thermally isolated from anything that changes temperature rapidly, and enclosed such that external temperature changes are integrated over at least tens of minutes. Then, the inside of the enclosure will reach its own thermal equilibrium and any external changes will be slowed enough to be tracked out by the GPS discipline. My recommendation would be to put it in a cast aluminum box (search the archives for cast aluminum box), but there are others who think you need to build a two foot cube out of cinderblocks and fire brick against a wall in the deepest external corner of your basement. OR, if my suspicion is correct that the temperature sensitivity is mostly the GPS time base, figure out a way to kludge the GPS to accept the disciplined OCXO as its time base. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
On Dec 12, 2014, at 10:53 PM, d...@irtelemetrics.com wrote: Hi Bob, or 1x10^-8 per volt. If it’s a 10 MHz OCXO. That would be 1x10^-14 per uV 4.7 x 10^-13 for 47 uV Good, so I'm not out to lunch here. ;) Thanks for verifying those numbers for me! What makes you believe that the OCXO’s temperature performance it not the issue? Because I can blow a hair dryer on it, and make very warm - almost hot to the touch and not see the phase or DAC change. Yet 2 degree thermal cycles in the room show up in the DAC and phase. I'm pretty sure it's not the OCXO, but if you know anything that would suggest otherwise, please do share. I’ve been through the math multiple times. I’ve compared your OCXO’s to the data on best parts on the market. Let’s see: You claim you are heating up the OCXO by 30 C or so. The frequency must be below 4x10^-13 to be below your other effect. If so, your OCXO would do 3x10^-12 over -40 to +85. That is not possible with an OCXO. What is the part number on the OCXO you are using? Who made the OCXO? Is there a spec sheet on the OCXO or a similar part from the same outfit? Dig in a bit and you will have a very hard time finding parts that are as good as the numbers I’ve been using. Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi Alex, Monitoring the temperature control loop of this OXCO is even easier than that. Currently instaled is a HP10811. It has a very handy oven monitor pin, that varies voltage with what the control does to keep temperature constant. (Those HP guys were really thinking!) Any time the oven has to react to something it's visible on that pin. Albeit, most of the stuff is in the 100uV or under level, but it's there. Currently there is a 8Ch 24bit DAQ card tied to this whole thing, and the card has proven to be more than stable enough to see what's going on. There is some correlation between the bulk supply voltage and DAC/Phase, so the next step is to chase that down. Just not exaxtly sure how it's getting in there. It's interesting what can be learned from looking at a bunch of data... The really interesting thing is what's going on with the GPS temperature. You can see it ramp temp slowly, then drop 1/2 deg F, then ramp up slowly, and drop again. One would guess that it's tied to CPU load or similar. The only thing that bothers me about that, is the fact that the GPS is very temp sensitive. It may very well be the limiting factor. I have yet to monitor the VCC to the GPS, so there might be something more to learn... 73, Dan just thinking; OXCO is one ovenized crystal oscillator with temperature control, better to say temperature stabilizer, thus if the outside temperature changes the control loop shall keep the internal temperature constant-- by definition, the function of the temperature control loop could be observed by the variation of the supply current of the oven. Also the reference voltage supplied from inside of the OCXO is coming from a voltage source which has stabilized temperature, therefore it is a relative stabil reference voltage source, which could be used to compare the stability of other voltages and thus, it could be found which voltage is moving with the environment's temperature. 73 Alex ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
...is the fact that the GPS is very temp sensitive... What have you observed, out of the GPS, with the temperature variations? On Sat, Dec 13, 2014 at 6:08 PM, d...@irtelemetrics.com wrote: Hi Alex, Monitoring the temperature control loop of this OXCO is even easier than that. Currently instaled is a HP10811. It has a very handy oven monitor pin, that varies voltage with what the control does to keep temperature constant. (Those HP guys were really thinking!) Any time the oven has to react to something it's visible on that pin. Albeit, most of the stuff is in the 100uV or under level, but it's there. Currently there is a 8Ch 24bit DAQ card tied to this whole thing, and the card has proven to be more than stable enough to see what's going on. There is some correlation between the bulk supply voltage and DAC/Phase, so the next step is to chase that down. Just not exaxtly sure how it's getting in there. It's interesting what can be learned from looking at a bunch of data... The really interesting thing is what's going on with the GPS temperature. You can see it ramp temp slowly, then drop 1/2 deg F, then ramp up slowly, and drop again. One would guess that it's tied to CPU load or similar. The only thing that bothers me about that, is the fact that the GPS is very temp sensitive. It may very well be the limiting factor. I have yet to monitor the VCC to the GPS, so there might be something more to learn... 73, Dan just thinking; OXCO is one ovenized crystal oscillator with temperature control, better to say temperature stabilizer, thus if the outside temperature changes the control loop shall keep the internal temperature constant-- by definition, the function of the temperature control loop could be observed by the variation of the supply current of the oven. Also the reference voltage supplied from inside of the OCXO is coming from a voltage source which has stabilized temperature, therefore it is a relative stabil reference voltage source, which could be used to compare the stability of other voltages and thus, it could be found which voltage is moving with the environment's temperature. 73 Alex ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
In response to Dan, Azelio wrote: What have you observed, out of the GPS, with the temperature variations? Also, when you say the GPS temperature, what, exactly, are you measuring/reporting? Is the GPS's own time base varying with temperature?** And how much thermal isolation is there between the various subsystems (GPS, PLL circuitry, OCXO, etc.) in your test setup? Some photos of the test setup could be helpful. Best regards, Charles ** I'm assuming that the GPS does not use the OCXO output for its own timing. That is such a good idea, I can't understand why more designers don't do it. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Dan wrote: It's interesting what can be learned from looking at a bunch of data... Sure enough, BUT: Never forget that this same methodology has suckered many researchers into claiming causal relationships between the birth rate in some small Peruvian village and the price of raw steel in Europe, and other such nonsense. Data mining is a thousand times more fraught with peril than simulating the operation of electronic circuits, and trusting simulations bites many engineers in the ass every day. The really interesting thing is what's going on with the GPS temperature. You can see it ramp temp slowly, then drop 1/2 deg F, then ramp up slowly, and drop again. What is the time scale of this cycle? Could it be associated with the lab HVAC system? [I asked in another message what, exactly, is being measured and reported as the GPS temperature, and how much thermal isolation there is between the various subsystems in the test setup.] Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi Dan, Have you varied the of the GPSDO board itself, say by covering it, shining a lamp on it, blowing a fan on it, or something? (It would be even better if you could vary the temperature of parts of it separately) If you're seeing supply voltage variations, you could then just vary the supply and see what happens. You may have done this already, but I just didn't see it mentioned. Angus. On Thu, 11 Dec 2014 07:13:14 -0500, you wrote: Yeah, I suffer from time-nuts digest lag, family lag, day job lag, among other things. So please excuse delayed responses... The oscillator has proven to be relatively immune to 'reasonable' changes in voltage, as would be expected. About the range of Numbers Bob Camp has suggested, or maybe even better. The EFC voltage is not an issue at this point. It was previously, and the solution to that was a low drift 'roll your own' design. It would be nice to replace it with a COTS part, but it looks like there aren't any available. Thus the reason for pinging the list. Sometimes you all pull things out of thin air... ;) That said, the LT3081 looks interesting. At the very least it's easily controllable from an external source. I've got a few on order, and if it pans out I'll report back here. What I'm after right now is in reality small. Temp cycles are somewhat apparent from looking at what the EFC voltage is doing locked with the GPSDO. It's on the order 10^-12 range, if I did my math right. It is visible, so it may be worth trying to fix. Of course, now that Bob has his new CS to play with anything I do is judged by a completely different standard! ;) Again, thanks for the responses! Dan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
** I'm assuming that the GPS does not use the OCXO output for its own timing. That is such a good idea, I can't understand why more designers don't do it. It adds to the cost. If the end-user only needs XO or TCXO quality timing, there's no incentive to increase the size and cost and power of the GPSDO product with a OCXO. But, you're right, it *is* a really good idea, and of course we all know the Trimble Thunderbolt does it this way. One reason why it's always the #1 favorite GPSDO among time nuts. Note that most high-end GNSS timing receivers go one better and simply have an external input for the clock. That way you feed your own lab clock into the receiver. If you have Rb/Cs/maser you would use that as the reference. It's what the national timing labs do, along with dual-frequency and post-processing and all the other tricks of the trade. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
tvb wrote: But, you're right, it *is* a really good idea, and of course we all know the Trimble Thunderbolt does it this way. One reason why it's always the #1 favorite GPSDO among time nuts. That and the fact that the PLL loop parameters can be fiddled over RS232. Certainly, I'm surprised that the better-grade commercial GPSDOs don't do it, but I'm downright flabbergasted that time nuts don't do their DIY projects that way. It's a huge trick to miss. Note that most high-end GNSS timing receivers go one better and simply have an external input for the clock. That way you feed your own lab clock into the receiver. If you have Rb/Cs/maser you would use that as the reference. It's what the national timing labs do, along with dual-frequency and post-processing and all the other tricks of the trade. I'm still waiting for the TAPR buy of such receivers, $250 each fully checked by someone named Tom Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi, What have you observed, out of the GPS, with the temperature variations? The test was simple. A couple of seconds of warm air from a hair dryer on low setting (the air coming out is 15C above ambient, so not very much heat at all) through a paper tube blowing on the GPS. That little change causes the phase to shift about 200nS in just a few seconds. That is, the GPS PPS phase compared to the OCXO phase shifts 200nS, and it happens over only a few seconds, literally almost instantly. It's an enormous change! I have checked that it's not electrical noise from the hair dryer, and I have repeated the test multiple times. Also, when you say the GPS temperature, what, exactly, are you measuring/reporting? Is the GPS's own time base varying with temperature?** And how much thermal isolation is there between the various subsystems (GPS, PLL circuitry, OCXO, etc.) in your test setup? ** I'm assuming that the GPS does not use the OCXO output for its own timing. That is such a good idea, I can't understand why more designers don't do it. Currently to measure the GPS temperature I have a K type TC taped to the top of the GPS RF shield. Since the temperature sensitivity was noticed, the GPS has been sitting under a wool sock with a 1Lb roll of solder sitting on that (That does help a bunch). Since the TC and GPS are under the wool sock the TC gets pretty good coupling to the GPS module itself. The GPS is mounted to a pine board right now, so has insulation underneath. The rest of the stuff (OXCO, GPSDO board, linear regulators/heatsink etc.) is sitting out in the open on the bench. Exposed to every possible air current, and even the front door being left open by my kids as they run in and out. The small temperature cycles on the GPS are about 5 to 7 minutes long. The HVAC cycles are about 45 minutes apart. So I believe these two are not related. I can clearly see the HVAC cycles and the 'ramp' waveform. As for what's causing the ramp in temperature on the GPS module, I have no idea. Any guess as to what is going on would be just that. It was just an interesting thing to note. The setup is a prototype and pretty ugly, but things are spaced out enough to be able to blow hot air on them with out hitting the other components. I can also cover and uncover individual components with a wool sock if need be. I've tried blowing the hot air on every other part of the system, and the GPS is the one that responds now. Previously the GPSDO DAC itself caused a similar response, but that has since been resolved. I'm well aware of the difference between cause/effect and correlation. (Everyone who ever eats Broccoli will die, you know. ;) ) It's the reason I've been been blowing hot air on stuff, to be sure there is a cause and effect relationship... It adds to the cost. If the end-user only needs XO or TCXO quality timing, there's no incentive to increase the size and cost and power of the GPSDO product with a OCXO. But, you're right, it *is* a really good idea, and of course we all know the Trimble Thunderbolt does it this way. One reason why it's always the #1 favorite GPSDO among time nuts. Note that most high-end GNSS timing receivers go one better and simply have an external input for the clock. That way you feed your own lab clock into the receiver. If you have Rb/Cs/maser you would use that as the reference. It's what the national timing labs do, along with dual-frequency and post-processing and all the other tricks of the trade. I think it would be agreat idea also. It's a wonder that more of the 'timing' receivers don't have that external clock option! I wonder what these Ublox parts use for a clock? Is it something frequency compatible with a 10Mhz source??? (Hmm, can we pry one apart to figure it out! ;) ) As for the GNSS units, are these receivers something that an average person can afford to get their hands on, or do you have to sell your house to buy one? :) Thanks, Dan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Note that most high-end GNSS timing receivers go one better and simply have an external input for the clock. That way you feed your own lab clock into the receiver. If you have Rb/Cs/maser you would use that as the reference. It's what the national timing labs do, along with dual-frequency and post-processing and all the other tricks of the trade. I'm still waiting for the TAPR buy of such receivers, $250 each fully checked by someone named Tom Best regards, Charles Charles, I've been collecting a set of matched, used dual-frequency GPS receivers just for this purpose, including borrowed units from other time-nuts. The goal is a full comparison among them and then pass them along to interested members. I'm getting position solutions at the cm level. Bug me in 2015 for an update. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Dan wrote: The test was simple. A couple of seconds of warm air from a hair dryer on low setting (the air coming out is 15C above ambient, so not very much heat at all) through a paper tube blowing on the GPS. That little change causes the phase to shift about 200nS in just a few seconds. That is, the GPS PPS phase compared to the OCXO phase shifts 200nS, and it happens over only a few seconds, literally almost instantly. It's an enormous change! LOL. A couple of seconds of warm air at 15C above ambient is a HUGE temperature transient for any sensitive electronics, especially anything with an oscillator. I would venture a guess that the lion's share of the drift you see is the GPS time base shooting off-frequency, but there are probably other effects, too (voltage regulators, to name just one). To me, a little change in this context might be blowing one warm breath toward the GPS unit from 18 away and seeing what happens over the next minute or two. But the GPS temperature sensitivity shouldn't be a big factor in actual use. The GPS should be thermally isolated from anything that changes temperature rapidly, and enclosed such that external temperature changes are integrated over at least tens of minutes. Then, the inside of the enclosure will reach its own thermal equilibrium and any external changes will be slowed enough to be tracked out by the GPS discipline. My recommendation would be to put it in a cast aluminum box (search the archives for cast aluminum box), but there are others who think you need to build a two foot cube out of cinderblocks and fire brick against a wall in the deepest external corner of your basement. OR, if my suspicion is correct that the temperature sensitivity is mostly the GPS time base, figure out a way to kludge the GPS to accept the disciplined OCXO as its time base. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints... -- WHY?
On Dec 12, 2014, at 12:28 AM, Charles Steinmetz csteinm...@yandex.com wrote: Bob wrote: Separate from the analysis of the voltage on the OCXO, there is another part to this: Ok, so why am I harping on the need for all this from a system standpoint ? We've been around this track a time or two before, me frustrated with your make it just good enough philosophy and you with my always do the best you can philosophy. We're not likely to persuade each other, or even influence anybody else, but I think it is worth going around at least one more time. 1) Adding stuff to a design that does not make it measurably better is simply a waste of money. Preliminary nit: I agree that any improvement that does not make something measurably better is of no value. Indeed, it is no improvement at all. But you didn't mean literally not measurably better -- you meant not better for the task at hand.” In the case at hand, the task is a GPSDO with a frequency vs temperature issue. The issue is coming from the OCXO and not the reference. Improving the reference will (in this case) have no impact on the problem. A digital caliper reading to 0.0001 is measurably better than a ruler graduated in 1/32 inch, although the difference is not important if one is measuring the thickness of a 2x4 for framing a house. But some day you may want to measure something besides a 2x4 On to the substance: Do the best you can isn't necessarily about adding anything to a design. It's about carefully determining an error budget and developing a design that meets the budget. Of course, you can set the design goals for each subsystem so that the overall system should jst work if everything else is perfect, or so that the system should work under most conditions, or so you'll never have to consider whether that subsystem might be contributing anything significant to the system errors. If the latter is no more difficult and no more expensive than either of the former, why WOULDN'T you design it that way? It is *rare* that an improvement does not impact cost or complexity. It most certainly is not the case in this situation. I was taught many years ago that good thinking doesn't cost any more than bad thinking, and I have generally found that to be true. Meaning, it is frequently the case that the best you can do is no more difficult and no more expensive than doing something less, it just takes better thinking and a more accurate analysis. Whenever that is the case, which IME is very often, doing less is, IMO, a design fault. Most often, it's a matter of, Why ground that capacitor there? Over here would be better, or Why use a noninverting amplifier? If you use an inverting amplifier, the HF rolloff can continue beyond unity gain, or something similar. Note, also, that many of the people asking questions on the list do not seem to have a thorough design specification for their project, and may not even know what all they will use a gizmo for. Settling for what a list pundit might think is good enough for the person's needs (e.g., residual phase noise floor ~ -150dB and reverse isolation of ~ 40dB for a buffer amplifier) may turn out to be inadequate when the person acquires some better oscillators and a DMTD setup and needs -175dB and 90dB. If they do the best they can the first time, they may not have to re-do it later. But - rather than looking at the system and it’s needs, we spin off to “improvements”. Inevitably the result is a -175 db solution to a -145 db problem. 2) Others read these threads and decide maybe I need to do that... 3) Still others look at this and decide If I need to do that, I'm not even going to start. That's not good either. Again, neither one is a problem if doing the best one can is no more difficult and no more expensive than doing something less. Except that in the actual example case at hand it very much is more expensive and more difficult. If someone has already done the good thinking and suggests a workable approach, and all you have to do is a sanity check to implement the idea (perhaps even improving on the design), again -- why WOULDN'T you? That’s not what’s being done here. The example case is not following the course you are talking about at all. There is always someone handy who is quick to point out all of the other ways to do things, so the person contemplating the project can evaluate the different approaches for himself. Sometimes, of course, going the next step up the best you can ladder involves an expensive part (e.g., silicon-on-sapphire semiconductors), or a much more complex design, or some use restriction (must be submerged in liquid nitrogen). In that case, one must think very carefully about the error budget and determine if that step is really necessary. But the vast majority of the time, we do not face that situation IME.
Re: [time-nuts] Linear voltage regulator hints... -- WHY?
I grew up in an industry where we called everything that was way overspec'ed, platinum-iridium xxx. I think there is a broad interest in e.g. low-tempco engineering or low-noise regulators and having some in the pocket designs that start with jellybean discrete parts and occasional hi-spec parts where they actually matter, is a great idea. Tim N3QE On Fri, Dec 12, 2014 at 8:09 AM, Bob Camp kb...@n1k.org wrote: On Dec 12, 2014, at 12:28 AM, Charles Steinmetz csteinm...@yandex.com wrote: Bob wrote: Separate from the analysis of the voltage on the OCXO, there is another part to this: Ok, so why am I harping on the need for all this from a system standpoint ? We've been around this track a time or two before, me frustrated with your make it just good enough philosophy and you with my always do the best you can philosophy. We're not likely to persuade each other, or even influence anybody else, but I think it is worth going around at least one more time. 1) Adding stuff to a design that does not make it measurably better is simply a waste of money. Preliminary nit: I agree that any improvement that does not make something measurably better is of no value. Indeed, it is no improvement at all. But you didn't mean literally not measurably better -- you meant not better for the task at hand.” In the case at hand, the task is a GPSDO with a frequency vs temperature issue. The issue is coming from the OCXO and not the reference. Improving the reference will (in this case) have no impact on the problem. A digital caliper reading to 0.0001 is measurably better than a ruler graduated in 1/32 inch, although the difference is not important if one is measuring the thickness of a 2x4 for framing a house. But some day you may want to measure something besides a 2x4 On to the substance: Do the best you can isn't necessarily about adding anything to a design. It's about carefully determining an error budget and developing a design that meets the budget. Of course, you can set the design goals for each subsystem so that the overall system should jst work if everything else is perfect, or so that the system should work under most conditions, or so you'll never have to consider whether that subsystem might be contributing anything significant to the system errors. If the latter is no more difficult and no more expensive than either of the former, why WOULDN'T you design it that way? It is *rare* that an improvement does not impact cost or complexity. It most certainly is not the case in this situation. I was taught many years ago that good thinking doesn't cost any more than bad thinking, and I have generally found that to be true. Meaning, it is frequently the case that the best you can do is no more difficult and no more expensive than doing something less, it just takes better thinking and a more accurate analysis. Whenever that is the case, which IME is very often, doing less is, IMO, a design fault. Most often, it's a matter of, Why ground that capacitor there? Over here would be better, or Why use a noninverting amplifier? If you use an inverting amplifier, the HF rolloff can continue beyond unity gain, or something similar. Note, also, that many of the people asking questions on the list do not seem to have a thorough design specification for their project, and may not even know what all they will use a gizmo for. Settling for what a list pundit might think is good enough for the person's needs (e.g., residual phase noise floor ~ -150dB and reverse isolation of ~ 40dB for a buffer amplifier) may turn out to be inadequate when the person acquires some better oscillators and a DMTD setup and needs -175dB and 90dB. If they do the best they can the first time, they may not have to re-do it later. But - rather than looking at the system and it’s needs, we spin off to “improvements”. Inevitably the result is a -175 db solution to a -145 db problem. 2) Others read these threads and decide maybe I need to do that... 3) Still others look at this and decide If I need to do that, I'm not even going to start. That's not good either. Again, neither one is a problem if doing the best one can is no more difficult and no more expensive than doing something less. Except that in the actual example case at hand it very much is more expensive and more difficult. If someone has already done the good thinking and suggests a workable approach, and all you have to do is a sanity check to implement the idea (perhaps even improving on the design), again -- why WOULDN'T you? That’s not what’s being done here. The example case is not following the course you are talking about at all. There is always someone handy who is quick to point out all of the other ways to do things, so the person contemplating the project can evaluate the different approaches for himself. Sometimes, of course, going the
Re: [time-nuts] Linear voltage regulator hints... -- WHY?
On 12/12/14, 5:09 AM, Bob Camp wrote: ——— Are we really that far apart - not really. We each are talking about two sides of the same coin. The real world is a messy place. Analysis often takes a back seat to the “fun of doing something”. That’s not to say it should though … And sometimes, the analysis is the fun part. These days, with awesome computational horsepower at your fingertips, anywhere, you can do analysis in places and times that are infeasible for bench work. I get a lot of useful analysis and modeling done on airplane flights across the country. No phone calls, no meetings to go to, no emails to respond to, no self induced distractions. 4-5 glorious mostly uninterrupted hours with forced seat time. (especially with more planes having 110V outlets at the seat) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints... -- WHY?
Hi On Dec 12, 2014, at 8:52 AM, Tim Shoppa tsho...@gmail.com wrote: I grew up in an industry where we called everything that was way overspec'ed, platinum-iridium xxx. I think there is a broad interest in e.g. low-tempco engineering or low-noise regulators and having some in the pocket designs that start with jellybean discrete parts and occasional hi-spec parts where they actually matter, is a great idea. Which is the reason I split this part of it off from the main thread. There are most certainly reasons why you would use low noise / low temp chef. / low aging references. Digging into that is not a bad thing and I’m in no way knocking that part of it. Bob Tim N3QE On Fri, Dec 12, 2014 at 8:09 AM, Bob Camp kb...@n1k.org wrote: On Dec 12, 2014, at 12:28 AM, Charles Steinmetz csteinm...@yandex.com wrote: Bob wrote: Separate from the analysis of the voltage on the OCXO, there is another part to this: Ok, so why am I harping on the need for all this from a system standpoint ? We've been around this track a time or two before, me frustrated with your make it just good enough philosophy and you with my always do the best you can philosophy. We're not likely to persuade each other, or even influence anybody else, but I think it is worth going around at least one more time. 1) Adding stuff to a design that does not make it measurably better is simply a waste of money. Preliminary nit: I agree that any improvement that does not make something measurably better is of no value. Indeed, it is no improvement at all. But you didn't mean literally not measurably better -- you meant not better for the task at hand.” In the case at hand, the task is a GPSDO with a frequency vs temperature issue. The issue is coming from the OCXO and not the reference. Improving the reference will (in this case) have no impact on the problem. A digital caliper reading to 0.0001 is measurably better than a ruler graduated in 1/32 inch, although the difference is not important if one is measuring the thickness of a 2x4 for framing a house. But some day you may want to measure something besides a 2x4 On to the substance: Do the best you can isn't necessarily about adding anything to a design. It's about carefully determining an error budget and developing a design that meets the budget. Of course, you can set the design goals for each subsystem so that the overall system should jst work if everything else is perfect, or so that the system should work under most conditions, or so you'll never have to consider whether that subsystem might be contributing anything significant to the system errors. If the latter is no more difficult and no more expensive than either of the former, why WOULDN'T you design it that way? It is *rare* that an improvement does not impact cost or complexity. It most certainly is not the case in this situation. I was taught many years ago that good thinking doesn't cost any more than bad thinking, and I have generally found that to be true. Meaning, it is frequently the case that the best you can do is no more difficult and no more expensive than doing something less, it just takes better thinking and a more accurate analysis. Whenever that is the case, which IME is very often, doing less is, IMO, a design fault. Most often, it's a matter of, Why ground that capacitor there? Over here would be better, or Why use a noninverting amplifier? If you use an inverting amplifier, the HF rolloff can continue beyond unity gain, or something similar. Note, also, that many of the people asking questions on the list do not seem to have a thorough design specification for their project, and may not even know what all they will use a gizmo for. Settling for what a list pundit might think is good enough for the person's needs (e.g., residual phase noise floor ~ -150dB and reverse isolation of ~ 40dB for a buffer amplifier) may turn out to be inadequate when the person acquires some better oscillators and a DMTD setup and needs -175dB and 90dB. If they do the best they can the first time, they may not have to re-do it later. But - rather than looking at the system and it’s needs, we spin off to “improvements”. Inevitably the result is a -175 db solution to a -145 db problem. 2) Others read these threads and decide maybe I need to do that... 3) Still others look at this and decide If I need to do that, I'm not even going to start. That's not good either. Again, neither one is a problem if doing the best one can is no more difficult and no more expensive than doing something less. Except that in the actual example case at hand it very much is more expensive and more difficult. If someone has already done the good thinking and suggests a workable approach, and all you have to do is a sanity check to implement the idea (perhaps even improving on the design), again -- why WOULDN'T
Re: [time-nuts] Linear voltage regulator hints...
Neil and Doug, Thanks for the part suggestions. I'll flag those as parts to study! Neil, Will share a sketch when at my desk next. Please do! A private email would be fine, and I would be interested in seeing an overengineerd solution ;) (Probably more curiosity than anything!) Thanks, Dan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi Bob, or 1x10^-8 per volt. If it’s a 10 MHz OCXO. That would be 1x10^-14 per uV 4.7 x 10^-13 for 47 uV Good, so I'm not out to lunch here. ;) Thanks for verifying those numbers for me! What makes you believe that the OCXO’s temperature performance it not the issue? Because I can blow a hair dryer on it, and make very warm - almost hot to the touch and not see the phase or DAC change. Yet 2 degree thermal cycles in the room show up in the DAC and phase. I'm pretty sure it's not the OCXO, but if you know anything that would suggest otherwise, please do share. I’d guess that the analog stuff is much better than it needs to be. At this point I would tend to agree, but don't have hard numbers to know for sure yet. Subject: Re: [time-nuts] Linear voltage regulator hints... -- WHY? Ok, so why am I harping on the “need” for all this from a system standpoint ? I have no idea. 1) Adding stuff to a design that does not make it measurably better is simply a waste of money. That’s ok if it’s your money. The stuff added needed to be added. It fixed an understood problem/limitation in the current hardware. It did make the system 'measurably' better. 2) Others read these threads and decide “maybe I need to do that..”. Now it’s a waste of somebody else’s money. If someone makes the decision to spec their part based on a somewhat random email, from some random thread, from an email list, they fully deserve the spend the extra $6 on parts. It serves them right for being so foolish! (Serously?!?) 3) Still others look at this and decide “If I need to do that, I’m not even going to start”. That’s not good either. This isn't extremely hard, but it is challenging. Maybe someone wanting to build a GPSDO should know what they're getting into. If a 10e-6/DegC scares them, you'd think coefficients of 1x10^-14 per uV would be worse. 4) Analysis *is* part of the design process. It should very much be part of this. It is. It's how the analog portion got to where it is now. What makes you think it isn't? 5) Focusing on a design aspect “because I can” is a very common thing. I do it all the time :) Because I fall into the trap often, I recognize just how much time gets soaked up on dead ends this way. I'm doing this because it's what I can easily contribute to the project. I'm spending considerable resources in terms of time and expenses studying and improving a piece of hardware to help a guy out, and to learn something along the way. 6) There are very real issues when doing this. Sorting out what’s real and what isn’t is far from easy. The more “noise” in with the signal, the less likely others are to figure out a good approach. Huh? Do you mean this particular response to the thread? Going back to the original post, the reason for the question was to look for a lower cost yet suitable replacement for the 'roll your own' design. One that could be shotgunned into the prototype to look for the thermal drift that is evident, and is not coming from the OCXO. This is part of the analysis you so eloquently spoke about above. As it turns out there are no parts that good. Moving foreword with the project, the COTS parts don't cut it, so at this point I see no other choice than to build something. You obviously have a lot of experience in this field. I'm glad that people like yourself are willing to share with the rest of us. But, please don't assume I'm incapable of navigating the cost vs. performance curve for a project, or that I'm incapable of determining if a part is over specified. It's insulting that you think so. Thanks, Dan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
just thinking; OXCO is one ovenized crystal oscillator with temperature control, better to say temperature stabilizer, thus if the outside temperature changes the control loop shall keep the internal temperature constant-- by definition, the function of the temperature control loop could be observed by the variation of the supply current of the oven. Also the reference voltage supplied from inside of the OCXO is coming from a voltage source which has stabilized temperature, therefore it is a relative stabil reference voltage source, which could be used to compare the stability of other voltages and thus, it could be found which voltage is moving with the environment's temperature. 73 Alex On 12/12/2014 7:53 PM, d...@irtelemetrics.com wrote: Hi Bob, or 1x10^-8 per volt. If it’s a 10 MHz OCXO. That would be 1x10^-14 per uV 4.7 x 10^-13 for 47 uV Good, so I'm not out to lunch here. ;) Thanks for verifying those numbers for me! What makes you believe that the OCXO’s temperature performance it not the issue? Because I can blow a hair dryer on it, and make very warm - almost hot to the touch and not see the phase or DAC change. Yet 2 degree thermal cycles in the room show up in the DAC and phase. I'm pretty sure it's not the OCXO, but if you know anything that would suggest otherwise, please do share. I’d guess that the analog stuff is much better than it needs to be. At this point I would tend to agree, but don't have hard numbers to know for sure yet. Subject: Re: [time-nuts] Linear voltage regulator hints... -- WHY? Ok, so why am I harping on the “need” for all this from a system standpoint ? I have no idea. 1) Adding stuff to a design that does not make it measurably better is simply a waste of money. That’s ok if it’s your money. The stuff added needed to be added. It fixed an understood problem/limitation in the current hardware. It did make the system 'measurably' better. 2) Others read these threads and decide “maybe I need to do that..”. Now it’s a waste of somebody else’s money. If someone makes the decision to spec their part based on a somewhat random email, from some random thread, from an email list, they fully deserve the spend the extra $6 on parts. It serves them right for being so foolish! (Serously?!?) 3) Still others look at this and decide “If I need to do that, I’m not even going to start”. That’s not good either. This isn't extremely hard, but it is challenging. Maybe someone wanting to build a GPSDO should know what they're getting into. If a 10e-6/DegC scares them, you'd think coefficients of 1x10^-14 per uV would be worse. 4) Analysis *is* part of the design process. It should very much be part of this. It is. It's how the analog portion got to where it is now. What makes you think it isn't? 5) Focusing on a design aspect “because I can” is a very common thing. I do it all the time :) Because I fall into the trap often, I recognize just how much time gets soaked up on dead ends this way. I'm doing this because it's what I can easily contribute to the project. I'm spending considerable resources in terms of time and expenses studying and improving a piece of hardware to help a guy out, and to learn something along the way. 6) There are very real issues when doing this. Sorting out what’s real and what isn’t is far from easy. The more “noise” in with the signal, the less likely others are to figure out a good approach. Huh? Do you mean this particular response to the thread? Going back to the original post, the reason for the question was to look for a lower cost yet suitable replacement for the 'roll your own' design. One that could be shotgunned into the prototype to look for the thermal drift that is evident, and is not coming from the OCXO. This is part of the analysis you so eloquently spoke about above. As it turns out there are no parts that good. Moving foreword with the project, the COTS parts don't cut it, so at this point I see no other choice than to build something. You obviously have a lot of experience in this field. I'm glad that people like yourself are willing to share with the rest of us. But, please don't assume I'm incapable of navigating the cost vs. performance curve for a project, or that I'm incapable of determining if a part is over specified. It's insulting that you think so. Thanks, Dan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Yeah, I suffer from time-nuts digest lag, family lag, day job lag, among other things. So please excuse delayed responses... The oscillator has proven to be relatively immune to 'reasonable' changes in voltage, as would be expected. About the range of Numbers Bob Camp has suggested, or maybe even better. The EFC voltage is not an issue at this point. It was previously, and the solution to that was a low drift 'roll your own' design. It would be nice to replace it with a COTS part, but it looks like there aren't any available. Thus the reason for pinging the list. Sometimes you all pull things out of thin air... ;) That said, the LT3081 looks interesting. At the very least it's easily controllable from an external source. I've got a few on order, and if it pans out I'll report back here. What I'm after right now is in reality small. Temp cycles are somewhat apparent from looking at what the EFC voltage is doing locked with the GPSDO. It's on the order 10^-12 range, if I did my math right. It is visible, so it may be worth trying to fix. Of course, now that Bob has his new CS to play with anything I do is judged by a completely different standard! ;) Again, thanks for the responses! Dan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi If your OCXO has a stability of +/-3x10^-10 over 0 to 60C (numbers picked to make math easy): 6x10^-10 / 60 = 1x10^-11 per C If the OCXO is 10X better than that (unlike) you are at 1x10^-12/C If the room temperature swings 1 C, you get a 1x10^-11 swing in the OCXO. Keep in mind that the OCXO also responds to things like gradients as much as it does to absolute temperature. If your EFC range is 1x10^-7 for 5V (pretty common): Each 1 mv change is 2 x10^-11. A 78L05 will hold 1 mv over 1C. Roughly 90% of them will hold that over 20C. That’s a cheap regulator for 2x10^-12. A 10 ppm / C reference will get you to 1x10^-13 / C You don’t *need* an EFC at 1x10^-7. Something 1/10 that size is probably good enough. Knocking it down to that level is just a couple of resistors. Way less money than fancy references. Bob On Dec 11, 2014, at 7:13 AM, d...@irtelemetrics.com wrote: Yeah, I suffer from time-nuts digest lag, family lag, day job lag, among other things. So please excuse delayed responses... The oscillator has proven to be relatively immune to 'reasonable' changes in voltage, as would be expected. About the range of Numbers Bob Camp has suggested, or maybe even better. The EFC voltage is not an issue at this point. It was previously, and the solution to that was a low drift 'roll your own' design. It would be nice to replace it with a COTS part, but it looks like there aren't any available. Thus the reason for pinging the list. Sometimes you all pull things out of thin air... ;) That said, the LT3081 looks interesting. At the very least it's easily controllable from an external source. I've got a few on order, and if it pans out I'll report back here. What I'm after right now is in reality small. Temp cycles are somewhat apparent from looking at what the EFC voltage is doing locked with the GPSDO. It's on the order 10^-12 range, if I did my math right. It is visible, so it may be worth trying to fix. Of course, now that Bob has his new CS to play with anything I do is judged by a completely different standard! ;) Again, thanks for the responses! Dan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
If the plan is to use a three-terminal regulator after all, I'd suggest not using a low-dropout (LDO) type if the raw input supply is noisy - the LDOs usually have PNP output transistors (for positive regulators), so may tend to have poorer HF input ripple rejection than equivalent ones with NPN passers. At low frequencies this is no problem since the regulator loop takes care of it, but as the loop rolls off, the PNP becomes a common-base amplifier, allowing more HF from the input to pass on through. I alluded to this in my previous post - from an input HF rejection perspective, it's usually best to use an NPN passer for positive supplies, and conversely a PNP for negative, working as an emitter-follower. If the raw input comes from a switching supply, there will tend to be a lot of HF ripple, so this could be a concern. If this is the case, another option is to have a two-stage regulation scheme with as much pre-regulation and filtering as possible. This of course eats into the overhead budget, so may not be practical in many situations. Ed ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
I was just looking at various modern LDOs, and I see that they are greatly improved wrt PSRR - I think the older style PNP passers have been supplanted by new topologies that also even include MOSFETs, so there should be plenty of choices out there. So, I'm changing my recommendation - to avoid using older type PNP output LDOs, while newer types should be OK - just be sure to consider the specs. Ed ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
e...@telight.com said: If the plan is to use a three-terminal regulator after all, I'd suggest not using a low-dropout (LDO) type if the raw input supply is noisy - the LDOs usually have PNP output transistors (for positive regulators), so may tend to have poorer HF input ripple rejection than equivalent ones with NPN passers. In this context, what is high? Why don't filter caps solve that end of the spectrum? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
There exists a newer generation of linear regulators with much lower noise, designed for sensitive analog loads. Here are some representative parts. Check Analog Devices' website for other options... ADM7170/7171/7172 6.5 V, Ultra Low Noise, High PSRR, Fast Transient Response CMOS LDO Doug R. -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of ed breya Sent: Thursday, December 11, 2014 9:48 AM To: time-nuts@febo.com Subject: Re: [time-nuts] Linear voltage regulator hints... If the plan is to use a three-terminal regulator after all, I'd suggest not using a low-dropout (LDO) type if the raw input supply is noisy - the LDOs usually have PNP output transistors (for positive regulators), so may tend to have poorer HF input ripple rejection than equivalent ones with NPN passers. At low frequencies this is no problem since the regulator loop takes care of it, but as the loop rolls off, the PNP becomes a common-base amplifier, allowing more HF from the input to pass on through. I alluded to this in my previous post - from an input HF rejection perspective, it's usually best to use an NPN passer for positive supplies, and conversely a PNP for negative, working as an emitter-follower. If the raw input comes from a switching supply, there will tend to be a lot of HF ripple, so this could be a concern. If this is the case, another option is to have a two-stage regulation scheme with as much pre-regulation and filtering as possible. This of course eats into the overhead budget, so may not be practical in many situations. Ed ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi Most OCXO’s will meet all spec’s with 1 to 10 mV RMS on the supply lead. That’s mV not uV. If the noise is flat in a 100 Hz to 100 KHz bandwidth, most will meet their ADEV specs with a mV RMS on the EFC line. Again mV not uV. The issue is pretty simple: Things like an EFC or supply FM modulate the OCXO. Phase / time (= what you care about) drops off as 1/f. It’s actually pretty hard to find a reference or DAC that is noisy enough to bother a typical OCXO. Bob On Dec 11, 2014, at 6:26 PM, Neil Schroeder gign...@gmail.com wrote: So I've done a lot of work in power lately and I can summarize some of this quickly: The lowest noise LDOs today are the TI TPSa4700/01 up to 36v/1a and about 4 uVRms noise, and the ADP7154/55 up to 5.5v and 600ma with only *0.9* uVRms above 100hz. Both feature great PSRR -and in the case of the ADI part don't even recommend filter caps at all. The TI however does still recommend some capacitance. Now most people's next question is how to get their ruby or their septuple-oven homebrew design powered by one. The quick answer is an error amplifier based ldo balancer for the most accurate distribution of current. Also helps with heat. Will share a sketch when at my desk next. On Thursday, December 11, 2014, Hal Murray hmur...@megapathdsl.net wrote: e...@telight.com javascript:; said: If the plan is to use a three-terminal regulator after all, I'd suggest not using a low-dropout (LDO) type if the raw input supply is noisy - the LDOs usually have PNP output transistors (for positive regulators), so may tend to have poorer HF input ripple rejection than equivalent ones with NPN passers. In this context, what is high? Why don't filter caps solve that end of the spectrum? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com javascript:; To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
I don't know if this is the right time to ask this but here goes. I have started a design for a linear power supply for the Beagleboard 5V 5-10A. Over-Voltage, short circuit and temp protection. Very low ripple and HF noise. I have been watching this thread and I am still not sure what device would give me what I want. I am not as good as some circuit designers here, to design a PS via discreet transistors. Dr. Bruce Griffiths comes to mind. He would probably do this with his eyes closed. So, I need to use a regulator chip. The TI TPS7A4700 looks great but it can only supply 1A. Any other candidates ? I am sorry if I am somehow asking an obvious question. -George On 12/11/2014 06:26 PM, Neil Schroeder wrote: So I've done a lot of work in power lately and I can summarize some of this quickly: The lowest noise LDOs today are the TI TPSa4700/01 up to 36v/1a and about 4 uVRms noise, and the ADP7154/55 up to 5.5v and 600ma with only *0.9* uVRms above 100hz. Both feature great PSRR -and in the case of the ADI part don't even recommend filter caps at all. The TI however does still recommend some capacitance. Now most people's next question is how to get their ruby or their septuple-oven homebrew design powered by one. The quick answer is an error amplifier based ldo balancer for the most accurate distribution of current. Also helps with heat. Will share a sketch when at my desk next. On Thursday, December 11, 2014, Hal Murray hmur...@megapathdsl.net wrote: e...@telight.com javascript:; said: If the plan is to use a three-terminal regulator after all, I'd suggest not using a low-dropout (LDO) type if the raw input supply is noisy - the LDOs usually have PNP output transistors (for positive regulators), so may tend to have poorer HF input ripple rejection than equivalent ones with NPN passers. In this context, what is high? Why don't filter caps solve that end of the spectrum? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com javascript:; To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi On Dec 11, 2014, at 7:37 PM, xaos x...@darksmile.net wrote: I don't know if this is the right time to ask this but here goes. I have started a design for a linear power supply for the Beagleboard 5V 5-10A. Over-Voltage, short circuit and temp protection. Very low ripple and HF noise. I have been watching this thread and I am still not sure what device would give me what I want. I am not as good as some circuit designers here, to design a PS via discreet transistors. Dr. Bruce Griffiths comes to mind. He would probably do this with his eyes closed. So, I need to use a regulator chip. The simple answer is that a 78L05 style regulator will do just fine. Bob The TI TPS7A4700 looks great but it can only supply 1A. Any other candidates ? I am sorry if I am somehow asking an obvious question. -George On 12/11/2014 06:26 PM, Neil Schroeder wrote: So I've done a lot of work in power lately and I can summarize some of this quickly: The lowest noise LDOs today are the TI TPSa4700/01 up to 36v/1a and about 4 uVRms noise, and the ADP7154/55 up to 5.5v and 600ma with only *0.9* uVRms above 100hz. Both feature great PSRR -and in the case of the ADI part don't even recommend filter caps at all. The TI however does still recommend some capacitance. Now most people's next question is how to get their ruby or their septuple-oven homebrew design powered by one. The quick answer is an error amplifier based ldo balancer for the most accurate distribution of current. Also helps with heat. Will share a sketch when at my desk next. On Thursday, December 11, 2014, Hal Murray hmur...@megapathdsl.net wrote: e...@telight.com javascript:; said: If the plan is to use a three-terminal regulator after all, I'd suggest not using a low-dropout (LDO) type if the raw input supply is noisy - the LDOs usually have PNP output transistors (for positive regulators), so may tend to have poorer HF input ripple rejection than equivalent ones with NPN passers. In this context, what is high? Why don't filter caps solve that end of the spectrum? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com javascript:; To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi Bob, Some numbers. Maybe you can double check my math, just to be sure I'm not getting something completely wrong. That is very possible, since I'm new here... ;) The DAC is moving up and down about 7.5 counts with room temp swings. 20 bit resolution at 6.6volts full scale output. 6.6 volts * 7.5counts / (2^20) = +/- 47uV. (This is verified as reasonable with a 24bit data logger, as it's seeing about +/-50 uV temp swings on EFC. Resolution of about 1uV.) Tuning sensitivity of the oscillator is 1Hz/10Volts. Or 47uV * 1Hz/10V = +/- 4.7uHz. The temp swing is +/- 2 degF with ~45 minute period. So, in the ballpark of your +/- 1 Deg C guess. +/-4.7uHz / 10e6 Hz oscillator = +/-4.7e-13, or near a 1e-12 full swing over 2.2 Deg C. (Or, am I completely out to lunch here???) I should qualify, there is aging/retrace here. It's in the range of 3e-11 per day right now, and I took the +/- 7.5counts off of what was left after removing the slope of the aging drift. The aging looks huge over a day compared to the thermal cycling. Currently the system has ~2ppm/C reference, and .04nV/C opamps. So, Yeah a little overkill. But these things are getting cheap nowadays, so why not? Before the 'good' reference and opamps, there was about 10 times as much swing in the PWM DAC over temp cycles. As you have suggested there is probably some room to 'relax the spec', and still be fine... Thanks, Dan Hi If your OCXO has a stability of +/-3x10^-10 over 0 to 60C (numbers picked to make math easy): 6x10^-10 / 60 = 1x10^-11 per C If the OCXO is 10X better than that (unlike) you are at 1x10^-12/C If the room temperature swings 1 C, you get a 1x10^-11 swing in the OCXO. Keep in mind that the OCXO also responds to things like gradients as much as it does to absolute temperature. If your EFC range is 1x10^-7 for 5V (pretty common): Each 1 mv change is 2 x10^-11. A 78L05 will hold 1 mv over 1C. Roughly 90% of them will hold that over 20C. That’s a cheap regulator for 2x10^-12. A 10 ppm / C reference will get you to 1x10^-13 / C You don’t *need* an EFC at 1x10^-7. Something 1/10 that size is probably good enough. Knocking it down to that level is just a couple of resistors. Way less money than fancy references. Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi On Dec 11, 2014, at 8:20 PM, d...@irtelemetrics.com wrote: Hi Bob, Some numbers. Maybe you can double check my math, just to be sure I'm not getting something completely wrong. That is very possible, since I'm new here... ;) The DAC is moving up and down about 7.5 counts with room temp swings. 20 bit resolution at 6.6volts full scale output. 6.6 volts * 7.5counts / (2^20) = +/- 47uV. (This is verified as reasonable with a 24bit data logger, as it's seeing about +/-50 uV temp swings on EFC. Resolution of about 1uV.) Tuning sensitivity of the oscillator is 1Hz/10Volts. Or 47uV * 1Hz/10V = +/- 4.7uHz. or 1x10^-8 per volt. If it’s a 10 MHz OCXO. That would be 1x10^-14 per uV 4.7 x 10^-13 for 47 uV The temp swing is +/- 2 degF with ~45 minute period. So, in the ballpark of your +/- 1 Deg C guess. That’s pretty normal for a modern HVAC system. +/-4.7uHz / 10e6 Hz oscillator = +/-4.7e-13, or near a 1e-12 full swing over 2.2 Deg C. 1x10^-12 for full swing is about right. (Or, am I completely out to lunch here???) I should qualify, there is aging/retrace here. It's in the range of 3e-11 per day right now, and I took the +/- 7.5counts off of what was left after removing the slope of the aging drift. That’s a very common (and legit) thing to do. The aging looks huge over a day compared to the thermal cycling. Currently the system has ~2ppm/C reference, and .04nV/C opamps. So, Yeah a little overkill. What makes you believe that the OCXO’s temperature performance it not the issue? 1x10^-12 per 2 C - 1x10^-10 over 100 C (say -30 to +70C). That’s a very good spec on an OCXO. Also consider that gradients could easily amplify the impact by 2X or more. But these things are getting cheap nowadays, so why not? Before the 'good' reference and opamps, there was about 10 times as much swing in the PWM DAC over temp cycles. As you have suggested there is probably some room to 'relax the spec', and still be fine… I’d guess that the analog stuff is much better than it needs to be. Bob Thanks, Dan Hi If your OCXO has a stability of +/-3x10^-10 over 0 to 60C (numbers picked to make math easy): 6x10^-10 / 60 = 1x10^-11 per C If the OCXO is 10X better than that (unlike) you are at 1x10^-12/C If the room temperature swings 1 C, you get a 1x10^-11 swing in the OCXO. Keep in mind that the OCXO also responds to things like gradients as much as it does to absolute temperature. If your EFC range is 1x10^-7 for 5V (pretty common): Each 1 mv change is 2 x10^-11. A 78L05 will hold 1 mv over 1C. Roughly 90% of them will hold that over 20C. That’s a cheap regulator for 2x10^-12. A 10 ppm / C reference will get you to 1x10^-13 / C You don’t *need* an EFC at 1x10^-7. Something 1/10 that size is probably good enough. Knocking it down to that level is just a couple of resistors. Way less money than fancy references. Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints... -- WHY?
Hi Separate from the analysis of the voltage on the OCXO, there is another part to this: Ok, so why am I harping on the “need” for all this from a system standpoint ? 1) Adding stuff to a design that does not make it measurably better is simply a waste of money. That’s ok if it’s your money. 2) Others read these threads and decide “maybe I need to do that..”. Now it’s a waste of somebody else’s money. 3) Still others look at this and decide “If I need to do that, I’m not even going to start”. That’s not good either. 4) Analysis *is* part of the design process. It should very much be part of this. 5) Focusing on a design aspect “because I can” is a very common thing. I do it all the time :) Because I fall into the trap often, I recognize just how much time gets soaked up on dead ends this way. 6) There are very real issues when doing this. Sorting out what’s real and what isn’t is far from easy. The more “noise” in with the signal, the less likely others are to figure out a good approach. I’m quite sure this thread will keep going for quite a while on references. At some point we will be talking about 1 pV / C 1KV designs with 0.1 nV/Hz noise levels. It worries me that people may believe that in some way that applies to a time or frequency standard …. Bob On Dec 11, 2014, at 8:47 PM, Bob Camp kb...@n1k.org wrote: Hi On Dec 11, 2014, at 8:20 PM, d...@irtelemetrics.com wrote: Hi Bob, Some numbers. Maybe you can double check my math, just to be sure I'm not getting something completely wrong. That is very possible, since I'm new here... ;) The DAC is moving up and down about 7.5 counts with room temp swings. 20 bit resolution at 6.6volts full scale output. 6.6 volts * 7.5counts / (2^20) = +/- 47uV. (This is verified as reasonable with a 24bit data logger, as it's seeing about +/-50 uV temp swings on EFC. Resolution of about 1uV.) Tuning sensitivity of the oscillator is 1Hz/10Volts. Or 47uV * 1Hz/10V = +/- 4.7uHz. or 1x10^-8 per volt. If it’s a 10 MHz OCXO. That would be 1x10^-14 per uV 4.7 x 10^-13 for 47 uV The temp swing is +/- 2 degF with ~45 minute period. So, in the ballpark of your +/- 1 Deg C guess. That’s pretty normal for a modern HVAC system. +/-4.7uHz / 10e6 Hz oscillator = +/-4.7e-13, or near a 1e-12 full swing over 2.2 Deg C. 1x10^-12 for full swing is about right. (Or, am I completely out to lunch here???) I should qualify, there is aging/retrace here. It's in the range of 3e-11 per day right now, and I took the +/- 7.5counts off of what was left after removing the slope of the aging drift. That’s a very common (and legit) thing to do. The aging looks huge over a day compared to the thermal cycling. Currently the system has ~2ppm/C reference, and .04nV/C opamps. So, Yeah a little overkill. What makes you believe that the OCXO’s temperature performance it not the issue? 1x10^-12 per 2 C - 1x10^-10 over 100 C (say -30 to +70C). That’s a very good spec on an OCXO. Also consider that gradients could easily amplify the impact by 2X or more. But these things are getting cheap nowadays, so why not? Before the 'good' reference and opamps, there was about 10 times as much swing in the PWM DAC over temp cycles. As you have suggested there is probably some room to 'relax the spec', and still be fine… I’d guess that the analog stuff is much better than it needs to be. Bob Thanks, Dan Hi If your OCXO has a stability of +/-3x10^-10 over 0 to 60C (numbers picked to make math easy): 6x10^-10 / 60 = 1x10^-11 per C If the OCXO is 10X better than that (unlike) you are at 1x10^-12/C If the room temperature swings 1 C, you get a 1x10^-11 swing in the OCXO. Keep in mind that the OCXO also responds to things like gradients as much as it does to absolute temperature. If your EFC range is 1x10^-7 for 5V (pretty common): Each 1 mv change is 2 x10^-11. A 78L05 will hold 1 mv over 1C. Roughly 90% of them will hold that over 20C. That’s a cheap regulator for 2x10^-12. A 10 ppm / C reference will get you to 1x10^-13 / C You don’t *need* an EFC at 1x10^-7. Something 1/10 that size is probably good enough. Knocking it down to that level is just a couple of resistors. Way less money than fancy references. Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi, George look for the book The art of electronics from Paul Horowitz and Winfield Hill, they describe how to design excellent electronic circuits, including power supplies 73 Alex On 12/11/2014 4:37 PM, xaos wrote: I don't know if this is the right time to ask this but here goes. I have started a design for a linear power supply for the Beagleboard 5V 5-10A. Over-Voltage, short circuit and temp protection. Very low ripple and HF noise. I have been watching this thread and I am still not sure what device would give me what I want. I am not as good as some circuit designers here, to design a PS via discreet transistors. Dr. Bruce Griffiths comes to mind. He would probably do this with his eyes closed. So, I need to use a regulator chip. The TI TPS7A4700 looks great but it can only supply 1A. Any other candidates ? I am sorry if I am somehow asking an obvious question. -George ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints... -- WHY?
Hi Charles, I hope you don't mind if I throw my two cents in, as this began as a question about my GPSDO project. We had a thermal drift problem that Dan traced to the PWM to EFC interface and resolved. The question to the list was whether there was a regulator package that had a built-in reference with good thermal performance. Somehow the thread went off on all the tangents, which can be good. In the process it became clear that there weren't any regulators that would fit our needs, so we would have to go with a reference and op-amp etc. So, now we just need to decide whether to use a pass transistor or a controllable regulator. The budget will probably result in a 25 or 50 cent pass transistor, a good(ish) op-amp and a reference that's multi-purposed for the board's other needs (ADC, RC integrator, etc). But it's certainly good to see what the other options are just in case. And if the project stays a two-off, then there's plenty of leeway to use better parts here and there if the pinouts are the same. Bob - AE6RV From: Charles Steinmetz csteinm...@yandex.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Thursday, December 11, 2014 11:28 PM Subject: Re: [time-nuts] Linear voltage regulator hints... -- WHY? Bob wrote: Separate from the analysis of the voltage on the OCXO, there is another part to this: Ok, so why am I harping on the need for all this from a system standpoint ? We've been around this track a time or two before, me frustrated with your make it just good enough philosophy and you with my always do the best you can philosophy. We're not likely to persuade each other, or even influence anybody else, but I think it is worth going around at least one more time. 1) Adding stuff to a design that does not make it measurably better is simply a waste of money. Preliminary nit: I agree that any improvement that does not make something measurably better is of no value. Indeed, it is no improvement at all. But you didn't mean literally not measurably better -- you meant not better for the task at hand. A digital caliper reading to 0.0001 is measurably better than a ruler graduated in 1/32 inch, although the difference is not important if one is measuring the thickness of a 2x4 for framing a house. But some day you may want to measure something besides a 2x4 On to the substance: Do the best you can isn't necessarily about adding anything to a design. It's about carefully determining an error budget and developing a design that meets the budget. Of course, you can set the design goals for each subsystem so that the overall system should jst work if everything else is perfect, or so that the system should work under most conditions, or so you'll never have to consider whether that subsystem might be contributing anything significant to the system errors. If the latter is no more difficult and no more expensive than either of the former, why WOULDN'T you design it that way? I was taught many years ago that good thinking doesn't cost any more than bad thinking, and I have generally found that to be true. Meaning, it is frequently the case that the best you can do is no more difficult and no more expensive than doing something less, it just takes better thinking and a more accurate analysis. Whenever that is the case, which IME is very often, doing less is, IMO, a design fault. Most often, it's a matter of, Why ground that capacitor there? Over here would be better, or Why use a noninverting amplifier? If you use an inverting amplifier, the HF rolloff can continue beyond unity gain, or something similar. Note, also, that many of the people asking questions on the list do not seem to have a thorough design specification for their project, and may not even know what all they will use a gizmo for. Settling for what a list pundit might think is good enough for the person's needs (e.g., residual phase noise floor ~ -150dB and reverse isolation of ~ 40dB for a buffer amplifier) may turn out to be inadequate when the person acquires some better oscillators and a DMTD setup and needs -175dB and 90dB. If they do the best they can the first time, they may not have to re-do it later. 2) Others read these threads and decide maybe I need to do that... 3) Still others look at this and decide If I need to do that, I'm not even going to start. That's not good either. Again, neither one is a problem if doing the best one can is no more difficult and no more expensive than doing something less. If someone has already done the good thinking and suggests a workable approach, and all you have to do is a sanity check to implement the idea (perhaps even improving on the design), again -- why WOULDN'T you? There is always someone handy who is quick to point out all of the other ways to do things, so the person contemplating the project can evaluate the different approaches
Re: [time-nuts] Linear voltage regulator hints... -- WHY?
Bob wrote: Separate from the analysis of the voltage on the OCXO, there is another part to this: Ok, so why am I harping on the need for all this from a system standpoint ? We've been around this track a time or two before, me frustrated with your make it just good enough philosophy and you with my always do the best you can philosophy. We're not likely to persuade each other, or even influence anybody else, but I think it is worth going around at least one more time. 1) Adding stuff to a design that does not make it measurably better is simply a waste of money. Preliminary nit: I agree that any improvement that does not make something measurably better is of no value. Indeed, it is no improvement at all. But you didn't mean literally not measurably better -- you meant not better for the task at hand. A digital caliper reading to 0.0001 is measurably better than a ruler graduated in 1/32 inch, although the difference is not important if one is measuring the thickness of a 2x4 for framing a house. But some day you may want to measure something besides a 2x4 On to the substance: Do the best you can isn't necessarily about adding anything to a design. It's about carefully determining an error budget and developing a design that meets the budget. Of course, you can set the design goals for each subsystem so that the overall system should jst work if everything else is perfect, or so that the system should work under most conditions, or so you'll never have to consider whether that subsystem might be contributing anything significant to the system errors. If the latter is no more difficult and no more expensive than either of the former, why WOULDN'T you design it that way? I was taught many years ago that good thinking doesn't cost any more than bad thinking, and I have generally found that to be true. Meaning, it is frequently the case that the best you can do is no more difficult and no more expensive than doing something less, it just takes better thinking and a more accurate analysis. Whenever that is the case, which IME is very often, doing less is, IMO, a design fault. Most often, it's a matter of, Why ground that capacitor there? Over here would be better, or Why use a noninverting amplifier? If you use an inverting amplifier, the HF rolloff can continue beyond unity gain, or something similar. Note, also, that many of the people asking questions on the list do not seem to have a thorough design specification for their project, and may not even know what all they will use a gizmo for. Settling for what a list pundit might think is good enough for the person's needs (e.g., residual phase noise floor ~ -150dB and reverse isolation of ~ 40dB for a buffer amplifier) may turn out to be inadequate when the person acquires some better oscillators and a DMTD setup and needs -175dB and 90dB. If they do the best they can the first time, they may not have to re-do it later. 2) Others read these threads and decide maybe I need to do that... 3) Still others look at this and decide If I need to do that, I'm not even going to start. That's not good either. Again, neither one is a problem if doing the best one can is no more difficult and no more expensive than doing something less. If someone has already done the good thinking and suggests a workable approach, and all you have to do is a sanity check to implement the idea (perhaps even improving on the design), again -- why WOULDN'T you? There is always someone handy who is quick to point out all of the other ways to do things, so the person contemplating the project can evaluate the different approaches for himself. Sometimes, of course, going the next step up the best you can ladder involves an expensive part (e.g., silicon-on-sapphire semiconductors), or a much more complex design, or some use restriction (must be submerged in liquid nitrogen). In that case, one must think very carefully about the error budget and determine if that step is really necessary. But the vast majority of the time, we do not face that situation IME. The bottom line is: There is no virtue in doing just enough, certainly not in the case of amateur projects that will not be manufactured in large numbers for slim profit (where every millipence must be saved, if the accountants are to be believed -- often, they shouldn't be, but that's another topic entirely). Never apologize for doing better than just enough, as long as doing so does not cause collateral problems. To me, that is the art of design -- knowing that the finished gizmo is the best I could make at the time and with the resources available. In philosophy-of-design circles, one sometimes hears that a race car should be designed so that everything is totally spent as it crosses the finish line -- the engine should explode, the transmission should break, and all four tires should blow out simultaneously. Anything
Re: [time-nuts] Linear voltage regulator hints...
On 12/10/2014 12:57 AM, Richard (Rick) Karlquist wrote: On 12/9/2014 3:02 PM, Bob Camp wrote: Here's an overnight ADEV plot against the new Cs of where we are in the project. Red is ADEV. Green is the TIC. Blue is the output of the GPSDO to Channel A and the Cs to Channel B of my 5335A measuring TI, using the 1PPS from my GPSDO to trigger the external gate. I see that the Cs phase has drifted down slightly vs my GPSDOe. I wonder if this is an indication of a calibration problem with the Cs or some subtle issue on my board? Looks perfectly normal to me. Your Cs is sensitive to magnetic field. Have you “zeroed” it out? No of course not, nobody does. (almost nobody …). Bob This reminds me of the great CBT demagnetizer debate at HP. Even Len Cutler didn't think this was necessary, at least in the 5071, and possibly the 5061. When Len says something is overkill, you can be sure of it. Anyway, we still had to support a CBT demagnetizer for customers who wanted it. The customer (with money to spend) is always right. The 5071 measures the C-field with a Zeeman line measurement and adjusts it if necessary. The C-field coil and it's main magnetization should be servoed like that for a modern Cesium. The possible problem lies if the magnetization causes a large enough gradient along the beampath, but it would have to be pretty strong to make any significant impact, considering the mymetal shields and other materials involved, so Len is naturally right. I have yet had a good reason to use my CBT degausser. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi On Dec 8, 2014, at 10:35 PM, Brooke Clarke bro...@pacific.net wrote: Hi Rich: Did you use the 723 or . . . .? As far as I know the 723 is supposed to have low noise. There are more modern parts with lower close in noise. Linear Technology has a number of them. Your filter caps take out the broadband stuff, close in is all that really matters. Bob Mail_Attachment -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html http://www.prc68.com/I/DietNutrition.html Richard (Rick) Karlquist wrote: On 12/8/2014 4:53 PM, Bert Kehren via time-nuts wrote: We solved that problem by attaching the regulators to the FRK back plate which is with fan control is kept within 0.01C. We did not do it for that purpose but found that we needed some more heat in order to keep the fan in an optimum fan speed. Rb, OCXO and Fan power transistor are on the back plate. Works for us. Bert Kehren When I designed the E1938A, I chose a reasonable looking voltage reference IC and put it inside the oven. I figured that was the end of it as far as tempco was concerned. It was, but it turned out that the *noise* of the reference was unacceptable and of course the oven does nothing to fix that. I had to switch to a lower noise reference. Rick Karlquist N6RK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hittite introduced a low noise reference a few years ago, but it was only low noise when filtered with a big cap. IOW, the cap did all the heavy lifting and the IC was nothing special. Good marketing, bad engineering. Rick On 12/9/2014 4:30 AM, Bob Camp wrote: Hi On Dec 8, 2014, at 10:35 PM, Brooke Clarke bro...@pacific.net wrote: Hi Rich: Did you use the 723 or . . . .? As far as I know the 723 is supposed to have low noise. There are more modern parts with lower close in noise. Linear Technology has a number of them. Your filter caps take out the broadband stuff, close in is all that really matters. Bob Mail_Attachment -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html http://www.prc68.com/I/DietNutrition.html Richard (Rick) Karlquist wrote: On 12/8/2014 4:53 PM, Bert Kehren via time-nuts wrote: We solved that problem by attaching the regulators to the FRK back plate which is with fan control is kept within 0.01C. We did not do it for that purpose but found that we needed some more heat in order to keep the fan in an optimum fan speed. Rb, OCXO and Fan power transistor are on the back plate. Works for us. Bert Kehren When I designed the E1938A, I chose a reasonable looking voltage reference IC and put it inside the oven. I figured that was the end of it as far as tempco was concerned. It was, but it turned out that the *noise* of the reference was unacceptable and of course the oven does nothing to fix that. I had to switch to a lower noise reference. Rick Karlquist N6RK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
I don't remember, but it wasn't a 723. Rick On 12/8/2014 7:35 PM, Brooke Clarke wrote: Hi Rich: Did you use the 723 or . . . .? As far as I know the 723 is supposed to have low noise. Mail_Attachment -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html http://www.prc68.com/I/DietNutrition.html Richard (Rick) Karlquist wrote: On 12/8/2014 4:53 PM, Bert Kehren via time-nuts wrote: We solved that problem by attaching the regulators to the FRK back plate which is with fan control is kept within 0.01C. We did not do it for that purpose but found that we needed some more heat in order to keep the fan in an optimum fan speed. Rb, OCXO and Fan power transistor are on the back plate. Works for us. Bert Kehren When I designed the E1938A, I chose a reasonable looking voltage reference IC and put it inside the oven. I figured that was the end of it as far as tempco was concerned. It was, but it turned out that the *noise* of the reference was unacceptable and of course the oven does nothing to fix that. I had to switch to a lower noise reference. Rick Karlquist N6RK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi Bob, I can't speak for Dan, but since he hasn't responded, I can speak a bit about the issue. As you know, my GPSDO uses a constant voltage TIC and the PWM output from a dsPIC33 to perform the DAC function. During testing we've found that one critical point is that the PWM voltage from the PIC changes with temperature. Dan managed to solve that for us by buffering the PWM with a 125 gate powered by a stable voltage. So, the temperature sensitivity issue is essentially solved. I would guess that he's looking around for a canned solution rather than using a good reference with an op-am. We need very stable voltages for both 2.5 and 3.3 unless I revisit the TIC's RC to make it useable at 3.3. On my prototype, I'm using an ADR-291G as a VREF for the ADC on the PIC. I had originally used LF33 regulators for the board voltage, but recently switched to using another ADR-291G with an op-amp and a suitable divider to get 3.3V to power the rest of the board, including the 125 gate. My prototype board was made with through-hole components, but I'm about convinced to do the next board on SMT. Good regulators would have been nice, but it sounds like we're going to be using references and op-amps to get what we need. Here's an overnight ADEV plot against the new Cs of where we are in the project. Red is ADEV. Green is the TIC. Blue is the output of the GPSDO to Channel A and the Cs to Channel B of my 5335A measuring TI, using the 1PPS from my GPSDO to trigger the external gate. I see that the Cs phase has drifted down slightly vs my GPSDOe. I wonder if this is an indication of a calibration problem with the Cs or some subtle issue on my board? This test will run throughout the day, so maybe that question will be answered. http://evoria.net/AE6RV/PRS-45A/GPSDOe.vs.Cs.12.9.14.10:19.png Bob From: Bob Camp kb...@n1k.org To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Monday, December 8, 2014 6:48 PM Subject: Re: [time-nuts] Linear voltage regulator hints... Hi Hopefully the issue (and question) is about stability of the EFC voltage. Any decent OCXO should have a voltage stability that’s well below it’s temperature stability when run off of a fairly standard regulator. As an example, An OCXO that does 5x10^-9 over 0 to 70 C probably has a voltage stability below 5x10^-10 for a 1% change. One percent is more than what a modern regulator should be moving when running an OCXO. Bob On Dec 8, 2014, at 7:33 PM, Dave M dgmin...@mediacombb.net wrote: Dan Kemppainen wrote: Hi, In playing with some oscillators and a GPSDO here, I think I'm seeing a voltage sensitivity issue. So, I started looking at the output voltage of various regulators vs. temp. Using standard LM/UA type linear regulators and some LDO's, they all appear to be pretty sensitive to temperature. (millivolt / few degrees Fahrenheit sort of sensitivity). Most of the datasheets seem to ignore temp sensitivity. Almost like they are so bad they don't want to publish it... Does anyone have hints on TO-220 or D-Pak type regulators that have really good temp coefficients and good line regulation? A few PPM/Deg C might be nice, if possible. Or am I into a 'roll you own' type design... Dan Yes, in order to get low PPM stability, you are going to roll your own. No 3-terminal regulator or reference that I know of can run an OXCO (heater and oscillator). What are your voltage and current requirements? Dave M ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi All, Thanks for the responses. I had a feeling the answer wouldn't be good, but was hoping someone would have a suggestion. There are currently a bunch of regulators in the 'system'. If there were some really good regulator out there, the shotgun approach would apply... Of course it is difficult to provide a good reference and pass transistor on the same die, but it was worth asking. Bert, The thought of temp control of the regulators crossed my mind. Not planning on going there unless I need to. But it was a thought, maybe if all else fails... Bob, There are more modern parts with lower close in noise. Linear Technology has a number of them. Your filter caps take out the broadband stuff, close in is all that really matters. Got any hints on which ones? Maybe a nice quiet regulator can be 'disciplined' with a better reference. Thanks, Dan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Voltage References are usually not able to deliver much more than a few 10mA. Having a stable reference means no big temperature gradient on the die, so that precludes a big pass transistor. Most likely, you will have to roll your own. Using TL431 types of shunt regulator with a single bipolar transistor yields a simple and high performing regulator (at least much higher than most 3 terminal series regulators) particularly if you use the Linear Tech equivalent part (forgot the part number at the moment, but look for shunt regulators) Didier KO4BB On December 8, 2014 4:59:24 PM CST, Bob Camp kb...@n1k.org wrote: Hi As with anything else it’s a matter of “what’s in your wallet”. The parts you are after are called voltage references rather than voltage regulators. You can get them well down into the low ppm’s / C or lower. The cutoff is more a function of “do you want to spend $100 or not” rather than a specific level you simply can’t get to. Bob On Dec 8, 2014, at 1:18 PM, Dan Kemppainen d...@irtelemetrics.com wrote: Hi, In playing with some oscillators and a GPSDO here, I think I'm seeing a voltage sensitivity issue. So, I started looking at the output voltage of various regulators vs. temp. Using standard LM/UA type linear regulators and some LDO's, they all appear to be pretty sensitive to temperature. (millivolt / few degrees Fahrenheit sort of sensitivity). Most of the datasheets seem to ignore temp sensitivity. Almost like they are so bad they don't want to publish it... Does anyone have hints on TO-220 or D-Pak type regulators that have really good temp coefficients and good line regulation? A few PPM/Deg C might be nice, if possible. Or am I into a 'roll you own' type design... Dan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Sent from my Motorola Droid Razr HD 4G LTE wireless tracker while I do other things. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
I'd recommend going with what Bob Stewart mentioned, using separate gates as buffers, operated from a better-grade reference, to shift from the noisier and driftier logic supplies, into the more critical circuits. It's simple, and can be powered from a modest reference circuit. If the logic circuits themselves need better supply noise and tempco performance, don't use any kind of three-terminal regulators - use a good opamp driving a pass transistor. Use a reference IC that has a buried zener for lowest noise - this eliminates all the low voltage references and three-terminal etc regulators that use band-gap references. The down side is that the good kind of reference ICs will need a higher (like 10V and up) operating voltage than may be available, so that complicates it. For a system using a conventional PC-style supply, with +5V and +12V available, an LM399, for example, could run from the +12V, along with the opamp circuitry, while the pass transistor could feed from the +5V, dropping to the +3.3V or whatever low logic supply is needed. For modest current requirement, use only an NPN pass transistor in emitter-follower mode. For higher currents, add another NPN emitter-follower in front of it for more drive - its collector can be supplied from the +12V via some limiting R, to ensure enough overhead. The opamp and associated network resistors, of course, should have performance commensurate with the reference, and sufficient for the application. Since there's also plenty of digital and PS noise around, a lot of bypassing in the right spots should help a lot. Ed ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi On Dec 9, 2014, at 11:31 AM, Bob Stewart b...@evoria.net wrote: Hi Bob, I can't speak for Dan, but since he hasn't responded, I can speak a bit about the issue. As you know, my GPSDO uses a constant voltage TIC and the PWM output from a dsPIC33 to perform the DAC function. During testing we've found that one critical point is that the PWM voltage from the PIC changes with temperature. Dan managed to solve that for us by buffering the PWM with a 125 gate powered by a stable voltage. So, the temperature sensitivity issue is essentially solved. I would guess that he's looking around for a canned solution rather than using a good reference with an op-am. We need very stable voltages for both 2.5 and 3.3 unless I revisit the TIC's RC to make it useable at 3.3. Most TIC’s are “radiometric” devices. If you feed all of the parts with the same voltage, the first order drift cancels out. Yes there are always second order effects. For what we do, a simple regulator is probably good enough. On my prototype, I'm using an ADR-291G as a VREF for the ADC on the PIC. I had originally used LF33 regulators for the board voltage, but recently switched to using another ADR-291G with an op-amp and a suitable divider to get 3.3V to power the rest of the board, including the 125 gate. My prototype board was made with through-hole components, but I'm about convinced to do the next board on SMT. Good regulators would have been nice, but it sounds like we're going to be using references and op-amps to get what we need. On the DAC out of the control loop, a stable reference may be useful. The same is true of a quiet one. With PWM(s) that means feeding the final gate(s) with a stable source. Since they likely pull 2 ma, a voltage reference should be fine. Here's an overnight ADEV plot against the new Cs of where we are in the project. Red is ADEV. Green is the TIC. Blue is the output of the GPSDO to Channel A and the Cs to Channel B of my 5335A measuring TI, using the 1PPS from my GPSDO to trigger the external gate. I see that the Cs phase has drifted down slightly vs my GPSDOe. I wonder if this is an indication of a calibration problem with the Cs or some subtle issue on my board? Looks perfectly normal to me. Your Cs is sensitive to magnetic field. Have you “zeroed” it out? No of course not, nobody does. (almost nobody …). Bob This test will run throughout the day, so maybe that question will be answered. http://evoria.net/AE6RV/PRS-45A/GPSDOe.vs.Cs.12.9.14.10:19.png Bob From: Bob Camp kb...@n1k.org To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Monday, December 8, 2014 6:48 PM Subject: Re: [time-nuts] Linear voltage regulator hints... Hi Hopefully the issue (and question) is about stability of the EFC voltage. Any decent OCXO should have a voltage stability that’s well below it’s temperature stability when run off of a fairly standard regulator. As an example, An OCXO that does 5x10^-9 over 0 to 70 C probably has a voltage stability below 5x10^-10 for a 1% change. One percent is more than what a modern regulator should be moving when running an OCXO. Bob On Dec 8, 2014, at 7:33 PM, Dave M dgmin...@mediacombb.net wrote: Dan Kemppainen wrote: Hi, In playing with some oscillators and a GPSDO here, I think I'm seeing a voltage sensitivity issue. So, I started looking at the output voltage of various regulators vs. temp. Using standard LM/UA type linear regulators and some LDO's, they all appear to be pretty sensitive to temperature. (millivolt / few degrees Fahrenheit sort of sensitivity). Most of the datasheets seem to ignore temp sensitivity. Almost like they are so bad they don't want to publish it... Does anyone have hints on TO-220 or D-Pak type regulators that have really good temp coefficients and good line regulation? A few PPM/Deg C might be nice, if possible. Or am I into a 'roll you own' type design... Dan Yes, in order to get low PPM stability, you are going to roll your own. No 3-terminal regulator or reference that I know of can run an OXCO (heater and oscillator). What are your voltage and current requirements? Dave M ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts
Re: [time-nuts] Linear voltage regulator hints...
Hi On Dec 9, 2014, at 11:57 AM, Dan Kemppainen d...@irtelemetrics.com wrote: Hi All, Thanks for the responses. I had a feeling the answer wouldn't be good, but was hoping someone would have a suggestion. There are currently a bunch of regulators in the 'system'. If there were some really good regulator out there, the shotgun approach would apply... Of course it is difficult to provide a good reference and pass transistor on the same die, but it was worth asking. Bert, The thought of temp control of the regulators crossed my mind. Not planning on going there unless I need to. But it was a thought, maybe if all else fails... Bob, There are more modern parts with lower close in noise. Linear Technology has a number of them. Your filter caps take out the broadband stuff, close in is all that really matters. Got any hints on which ones? Maybe a nice quiet regulator can be 'disciplined' with a better reference. http://www.linear.com/product/LTC6655 I believe that if you are trying to regulate the entire OCXO supply, you are doing the wrong thing and chasing the wrong problem …. Bob Thanks, Dan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi, On 12/09/2014 10:30 PM, ed breya wrote: I'd recommend going with what Bob Stewart mentioned, using separate gates as buffers, operated from a better-grade reference, to shift from the noisier and driftier logic supplies, into the more critical circuits. It's simple, and can be powered from a modest reference circuit. I've used this technique myself with great success. Nice way to convert dirty supply digital bits into benign noise supplies digital bits. If the logic circuits themselves need better supply noise and tempco performance, don't use any kind of three-terminal regulators - use a good opamp driving a pass transistor. Use a reference IC that has a buried zener for lowest noise - this eliminates all the low voltage references and three-terminal etc regulators that use band-gap references. The down side is that the good kind of reference ICs will need a higher (like 10V and up) operating voltage than may be available, so that complicates it. One should not trust the transition levels of logic to do any sine to square shaping. Most of that should have already been done before it meets the inherent comparator level of a logic gate. That you have sensitivity to power supply traceable to gate comparator voltage is a sign that you need to shape up first. Only once you have jolly good slew-rate you can hit a logical gate for further shaping, and that's when swapping power-supply using the above trick should be a trivial exercise . Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi Ed, I just wanted to clarify this, so that credit goes where it's due. Dan is helping me with my GPSDO project, and he was the one who came up with the idea of putting the 125 gate on with a good power source. Left to myself, I'd still be trying to figure out how to cancel the thermal noise. Bob From: ed breya e...@telight.com To: time-nuts@febo.com Sent: Tuesday, December 9, 2014 3:30 PM Subject: Re: [time-nuts] Linear voltage regulator hints... I'd recommend going with what Bob Stewart mentioned, using separate gates as buffers, operated from a better-grade reference, to shift from the noisier and driftier logic supplies, into the more critical circuits. It's simple, and can be powered from a modest reference circuit. If the logic circuits themselves need better supply noise and tempco performance, don't use any kind of three-terminal regulators - use a good opamp driving a pass transistor. Use a reference IC that has a buried zener for lowest noise - this eliminates all the low voltage references and three-terminal etc regulators that use band-gap references. The down side is that the good kind of reference ICs will need a higher (like 10V and up) operating voltage than may be available, so that complicates it. For a system using a conventional PC-style supply, with +5V and +12V available, an LM399, for example, could run from the +12V, along with the opamp circuitry, while the pass transistor could feed from the +5V, dropping to the +3.3V or whatever low logic supply is needed. For modest current requirement, use only an NPN pass transistor in emitter-follower mode. For higher currents, add another NPN emitter-follower in front of it for more drive - its collector can be supplied from the +12V via some limiting R, to ensure enough overhead. The opamp and associated network resistors, of course, should have performance commensurate with the reference, and sufficient for the application. Since there's also plenty of digital and PS noise around, a lot of bypassing in the right spots should help a lot. Ed ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
On 12/9/2014 1:30 PM, ed breya wrote: buried zener for lowest noise - this eliminates all the low voltage references and three-terminal etc regulators that use band-gap references. The down side is that the good kind of reference ICs will need a higher (like 10V and up) operating voltage than may be available, so that complicates it. Great post, Ed. I might add that my understanding of band gap regulators is that they rely on amplifying a small DC difference in voltage between two transistors. This also amplifies the SUM of the noise of the respective inputs, which jacks up the noise to much more than a good zener. Because of physics, no band gap reference will ever be low noise. Rick Karlquist N6RK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
On 12/9/2014 3:02 PM, Bob Camp wrote: Here's an overnight ADEV plot against the new Cs of where we are in the project. Red is ADEV. Green is the TIC. Blue is the output of the GPSDO to Channel A and the Cs to Channel B of my 5335A measuring TI, using the 1PPS from my GPSDO to trigger the external gate. I see that the Cs phase has drifted down slightly vs my GPSDOe. I wonder if this is an indication of a calibration problem with the Cs or some subtle issue on my board? Looks perfectly normal to me. Your Cs is sensitive to magnetic field. Have you “zeroed” it out? No of course not, nobody does. (almost nobody …). Bob This reminds me of the great CBT demagnetizer debate at HP. Even Len Cutler didn't think this was necessary, at least in the 5071, and possibly the 5061. When Len says something is overkill, you can be sure of it. Anyway, we still had to support a CBT demagnetizer for customers who wanted it. The customer (with money to spend) is always right. The 5071 measures the C-field with a Zeeman line measurement and adjusts it if necessary. Rick Karlquist N6RK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi On Dec 9, 2014, at 6:57 PM, Richard (Rick) Karlquist rich...@karlquist.com wrote: On 12/9/2014 3:02 PM, Bob Camp wrote: Here's an overnight ADEV plot against the new Cs of where we are in the project. Red is ADEV. Green is the TIC. Blue is the output of the GPSDO to Channel A and the Cs to Channel B of my 5335A measuring TI, using the 1PPS from my GPSDO to trigger the external gate. I see that the Cs phase has drifted down slightly vs my GPSDOe. I wonder if this is an indication of a calibration problem with the Cs or some subtle issue on my board? Looks perfectly normal to me. Your Cs is sensitive to magnetic field. Have you “zeroed” it out? No of course not, nobody does. (almost nobody …). Bob This reminds me of the great CBT demagnetizer debate at HP. Even Len Cutler didn't think this was necessary, at least in the 5071, and possibly the 5061. When Len says something is overkill, you can be sure of it. Anyway, we still had to support a CBT demagnetizer for customers who wanted it. The customer (with money to spend) is always right. The 5071 measures the C-field with a Zeeman line measurement and adjusts it if necessary. … and it seems to do *something* roughly every 24 hours …. That might include “react to the heating turning off in the building ..”. Bob Rick Karlquist N6RK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi All, Take a look on the low noise 1.5A LDO regulator LT1963 and 500 mA LT1763. Voltage regulation depend on how good is the circuit behaviour with respect to Noise, PSRR, Line regulation and Load regulation. For instance some LT regulators like LT1117, 1085 and 1086 have 1% of Line and Load regulation but have worst noise specs than LT1963, LT1763, MCP1825, MCP1826. Regards, Vasco Soares - Original Message - From: Dan Kemppainen d...@irtelemetrics.com To: time-nuts@febo.com Sent: Tuesday, December 09, 2014 4:57 PM Subject: Re: [time-nuts] Linear voltage regulator hints... Hi All, Thanks for the responses. I had a feeling the answer wouldn't be good, but was hoping someone would have a suggestion. There are currently a bunch of regulators in the 'system'. If there were some really good regulator out there, the shotgun approach would apply... Of course it is difficult to provide a good reference and pass transistor on the same die, but it was worth asking. Bert, The thought of temp control of the regulators crossed my mind. Not planning on going there unless I need to. But it was a thought, maybe if all else fails... Bob, There are more modern parts with lower close in noise. Linear Technology has a number of them. Your filter caps take out the broadband stuff, close in is all that really matters. Got any hints on which ones? Maybe a nice quiet regulator can be 'disciplined' with a better reference. Thanks, Dan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
about linear regulators: http://www.analog.com/static/imported-files/tutorials/MT-087.pdf 73 Alex ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
That seems to be generally true, but as always there are outliers. The LT1034 bandgap reference has 6uVp-p of low frequency noise at 2.5V, which compares favorably with the 20uVp-p of noise at 6.95V of the LM399. Of course, for many applications, you will have to amplify the 2V reference to what you need, which will bring up additional noise while the 6.95V of the LM399 may be closer to what you need. Of course, the tempco of the LT1034 does not even get close to that of the LM399, but it is not thermostatically regulated and draws considerably lower power. You can't have everything :) I observe that the LT1034 has two outputs, the high quality 2.5V and a lower quality 7V. http://www.linear.com/parametric/Shunt_Voltage_References Didier KO4BB On Tue, Dec 9, 2014 at 5:51 PM, Richard (Rick) Karlquist rich...@karlquist.com wrote: On 12/9/2014 1:30 PM, ed breya wrote: buried zener for lowest noise - this eliminates all the low voltage references and three-terminal etc regulators that use band-gap references. The down side is that the good kind of reference ICs will need a higher (like 10V and up) operating voltage than may be available, so that complicates it. Great post, Ed. I might add that my understanding of band gap regulators is that they rely on amplifying a small DC difference in voltage between two transistors. This also amplifies the SUM of the noise of the respective inputs, which jacks up the noise to much more than a good zener. Because of physics, no band gap reference will ever be low noise. Rick Karlquist N6RK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Linear voltage regulator hints...
Hi, In playing with some oscillators and a GPSDO here, I think I'm seeing a voltage sensitivity issue. So, I started looking at the output voltage of various regulators vs. temp. Using standard LM/UA type linear regulators and some LDO's, they all appear to be pretty sensitive to temperature. (millivolt / few degrees Fahrenheit sort of sensitivity). Most of the datasheets seem to ignore temp sensitivity. Almost like they are so bad they don't want to publish it... Does anyone have hints on TO-220 or D-Pak type regulators that have really good temp coefficients and good line regulation? A few PPM/Deg C might be nice, if possible. Or am I into a 'roll you own' type design... Dan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Dan - Almost all the 3-terminal 7805-style regulators are going to have tempcos near -100 or -120PPM/DegC. Bare 5.6V zener has a tempco closer to 40PPM/DEGC. I don't know anything that combines the reference with the pass device in the same package and gets to a few PPM/degC. Obviously few-PPM references are readily available. Tim N3QE On Mon, Dec 8, 2014 at 1:18 PM, Dan Kemppainen d...@irtelemetrics.com wrote: Hi, In playing with some oscillators and a GPSDO here, I think I'm seeing a voltage sensitivity issue. So, I started looking at the output voltage of various regulators vs. temp. Using standard LM/UA type linear regulators and some LDO's, they all appear to be pretty sensitive to temperature. (millivolt / few degrees Fahrenheit sort of sensitivity). Most of the datasheets seem to ignore temp sensitivity. Almost like they are so bad they don't want to publish it... Does anyone have hints on TO-220 or D-Pak type regulators that have really good temp coefficients and good line regulation? A few PPM/Deg C might be nice, if possible. Or am I into a 'roll you own' type design... Dan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi As with anything else it’s a matter of “what’s in your wallet”. The parts you are after are called voltage references rather than voltage regulators. You can get them well down into the low ppm’s / C or lower. The cutoff is more a function of “do you want to spend $100 or not” rather than a specific level you simply can’t get to. Bob On Dec 8, 2014, at 1:18 PM, Dan Kemppainen d...@irtelemetrics.com wrote: Hi, In playing with some oscillators and a GPSDO here, I think I'm seeing a voltage sensitivity issue. So, I started looking at the output voltage of various regulators vs. temp. Using standard LM/UA type linear regulators and some LDO's, they all appear to be pretty sensitive to temperature. (millivolt / few degrees Fahrenheit sort of sensitivity). Most of the datasheets seem to ignore temp sensitivity. Almost like they are so bad they don't want to publish it... Does anyone have hints on TO-220 or D-Pak type regulators that have really good temp coefficients and good line regulation? A few PPM/Deg C might be nice, if possible. Or am I into a 'roll you own' type design... Dan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Dan Kemppainen wrote: Hi, In playing with some oscillators and a GPSDO here, I think I'm seeing a voltage sensitivity issue. So, I started looking at the output voltage of various regulators vs. temp. Using standard LM/UA type linear regulators and some LDO's, they all appear to be pretty sensitive to temperature. (millivolt / few degrees Fahrenheit sort of sensitivity). Most of the datasheets seem to ignore temp sensitivity. Almost like they are so bad they don't want to publish it... Does anyone have hints on TO-220 or D-Pak type regulators that have really good temp coefficients and good line regulation? A few PPM/Deg C might be nice, if possible. Or am I into a 'roll you own' type design... Dan Yes, in order to get low PPM stability, you are going to roll your own. No 3-terminal regulator or reference that I know of can run an OXCO (heater and oscillator). What are your voltage and current requirements? Dave M ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi Hopefully the issue (and question) is about stability of the EFC voltage. Any decent OCXO should have a voltage stability that’s well below it’s temperature stability when run off of a fairly standard regulator. As an example, An OCXO that does 5x10^-9 over 0 to 70 C probably has a voltage stability below 5x10^-10 for a 1% change. One percent is more than what a modern regulator should be moving when running an OCXO. Bob On Dec 8, 2014, at 7:33 PM, Dave M dgmin...@mediacombb.net wrote: Dan Kemppainen wrote: Hi, In playing with some oscillators and a GPSDO here, I think I'm seeing a voltage sensitivity issue. So, I started looking at the output voltage of various regulators vs. temp. Using standard LM/UA type linear regulators and some LDO's, they all appear to be pretty sensitive to temperature. (millivolt / few degrees Fahrenheit sort of sensitivity). Most of the datasheets seem to ignore temp sensitivity. Almost like they are so bad they don't want to publish it... Does anyone have hints on TO-220 or D-Pak type regulators that have really good temp coefficients and good line regulation? A few PPM/Deg C might be nice, if possible. Or am I into a 'roll you own' type design... Dan Yes, in order to get low PPM stability, you are going to roll your own. No 3-terminal regulator or reference that I know of can run an OXCO (heater and oscillator). What are your voltage and current requirements? Dave M ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Am 08.12.2014 um 19:18 schrieb Dan Kemppainen: Hi, In playing with some oscillators and a GPSDO here, I think I'm seeing a voltage sensitivity issue. So, I started looking at the output voltage of various regulators vs. temp. Using standard LM/UA type linear regulators and some LDO's, they all appear to be pretty sensitive to temperature. (millivolt / few degrees Fahrenheit sort of sensitivity). Most of the datasheets seem to ignore temp sensitivity. Almost like they are so bad they don't want to publish it... Does anyone have hints on TO-220 or D-Pak type regulators that have really good temp coefficients and good line regulation? A few PPM/Deg C might be nice, if possible. Or am I into a 'roll you own' type design... Dan Hi Dan, I like to use the universal LM723C or µA723C, manuf. eg. Ti or NS Short description: it contains a temperature compensated reference source Vref Zener, ext. filter C is connectable to further reduce noise abt. 150 ppm/°K offset drift, but possible to work with ext. ref. as eg. LM129, 1n82x, LM399 etc. still available in N (DIL14), J, U, FK packages The LM723 can produce up to 150mA of output current without additional transistors hp did use it quite often in their equipment. Lot of example circuits and hints can be found in the internet to avoid unwanted oscillations use ceramic Cs as close as possible connected to the circuit. Good luck, Arnold, DK2WT ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
We solved that problem by attaching the regulators to the FRK back plate which is with fan control is kept within 0.01C. We did not do it for that purpose but found that we needed some more heat in order to keep the fan in an optimum fan speed. Rb, OCXO and Fan power transistor are on the back plate. Works for us. Bert Kehren In a message dated 12/8/2014 7:33:46 P.M. Eastern Standard Time, dgmin...@mediacombb.net writes: Dan Kemppainen wrote: Hi, In playing with some oscillators and a GPSDO here, I think I'm seeing a voltage sensitivity issue. So, I started looking at the output voltage of various regulators vs. temp. Using standard LM/UA type linear regulators and some LDO's, they all appear to be pretty sensitive to temperature. (millivolt / few degrees Fahrenheit sort of sensitivity). Most of the datasheets seem to ignore temp sensitivity. Almost like they are so bad they don't want to publish it... Does anyone have hints on TO-220 or D-Pak type regulators that have really good temp coefficients and good line regulation? A few PPM/Deg C might be nice, if possible. Or am I into a 'roll you own' type design... Dan Yes, in order to get low PPM stability, you are going to roll your own. No 3-terminal regulator or reference that I know of can run an OXCO (heater and oscillator). What are your voltage and current requirements? Dave M ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
On 12/8/2014 4:53 PM, Bert Kehren via time-nuts wrote: We solved that problem by attaching the regulators to the FRK back plate which is with fan control is kept within 0.01C. We did not do it for that purpose but found that we needed some more heat in order to keep the fan in an optimum fan speed. Rb, OCXO and Fan power transistor are on the back plate. Works for us. Bert Kehren When I designed the E1938A, I chose a reasonable looking voltage reference IC and put it inside the oven. I figured that was the end of it as far as tempco was concerned. It was, but it turned out that the *noise* of the reference was unacceptable and of course the oven does nothing to fix that. I had to switch to a lower noise reference. Rick Karlquist N6RK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Linear voltage regulator hints...
Hi Rich: Did you use the 723 or . . . .? As far as I know the 723 is supposed to have low noise. Mail_Attachment -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html http://www.prc68.com/I/DietNutrition.html Richard (Rick) Karlquist wrote: On 12/8/2014 4:53 PM, Bert Kehren via time-nuts wrote: We solved that problem by attaching the regulators to the FRK back plate which is with fan control is kept within 0.01C. We did not do it for that purpose but found that we needed some more heat in order to keep the fan in an optimum fan speed. Rb, OCXO and Fan power transistor are on the back plate. Works for us. Bert Kehren When I designed the E1938A, I chose a reasonable looking voltage reference IC and put it inside the oven. I figured that was the end of it as far as tempco was concerned. It was, but it turned out that the *noise* of the reference was unacceptable and of course the oven does nothing to fix that. I had to switch to a lower noise reference. Rick Karlquist N6RK ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
