Re: [time-nuts] 50 ohm Driver
One comment on the parallel AC gate approach. It may not be directly applicable to Martyn's issue, but there is a common confusion about the value of the summing resistors. Per Tom Clark, who came up with the idea, they are *not* intended to provide a near-end line termination to 50 ohms, but are simply there to protect the paralleled devices if the gates have slightly different delays (in which case one gate could end up sinking the other two). So, the commonly used 47 ohm value isn't magic. You can use a lower value, and thus get more voltage at the far end. I haven't experimented to see how far you can take that idea before destroying gates. John On 3/4/2015 5:26 AM, Martyn Smith wrote: Hello, A quick question. My output driver for a simple amplifier. I use three gates (in parallel with resistors) from a 74AC14 to give me about 0-3.2V into 50 ohm. I want to have a driver that gives me a full 0-5V (at least 0-4.5V) swing into 50 ohms. Can anyone recommend an IC that can delivery this. But it needs to have similar jitter performance to the 74AC14. I use it up to 10 MHz. Best Regards Martyn ___ 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] 50 ohm Driver
5V into 50 Ohms means 100 mA. Perhaps you need a medium power transistor amplifier or opamp. Bob On Wednesday, March 4, 2015 6:09 AM, Martyn Smith mar...@ptsyst.com wrote: Hello, A quick question. My output driver for a simple amplifier. I use three gates (in parallel with resistors) from a 74AC14 to give me about 0-3.2V into 50 ohm. I want to have a driver that gives me a full 0-5V (at least 0-4.5V) swing into 50 ohms. Can anyone recommend an IC that can delivery this. But it needs to have similar jitter performance to the 74AC14. I use it up to 10 MHz. Best Regards Martyn ___ 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] 50 ohm Driver
Building on top of John's comments, if you are using a logic gate, look at the maximum output (pull up) current per pin, set the series resistor so that this current is not exceeded into a short, then also see if there is a maximum total current draw for all gates combined, or some power input pin, and do not exceed that. You can also look at switching the termination resistor from a simple 50 Ohm resistor to ground, to a Thevenin load, which is 100 Ohms from +V to the load point, and another 100 Ohm resistor from the load point to ground. This way you still have a 50 Ohm termination, but only draw one half the DC current. In the event of no input, the receiver voltage will go to half scale. Make sure your system will not misbehave when this happens. Alternate driver is to use a video line driver with sufficient bandwidth. --- Graham / KE9H == On Wed, Mar 4, 2015 at 7:54 AM, John Ackermann N8UR j...@febo.com wrote: One comment on the parallel AC gate approach. It may not be directly applicable to Martyn's issue, but there is a common confusion about the value of the summing resistors. Per Tom Clark, who came up with the idea, they are *not* intended to provide a near-end line termination to 50 ohms, but are simply there to protect the paralleled devices if the gates have slightly different delays (in which case one gate could end up sinking the other two). So, the commonly used 47 ohm value isn't magic. You can use a lower value, and thus get more voltage at the far end. I haven't experimented to see how far you can take that idea before destroying gates. John On 3/4/2015 5:26 AM, Martyn Smith wrote: Hello, A quick question. My output driver for a simple amplifier. I use three gates (in parallel with resistors) from a 74AC14 to give me about 0-3.2V into 50 ohm. I want to have a driver that gives me a full 0-5V (at least 0-4.5V) swing into 50 ohms. Can anyone recommend an IC that can delivery this. But it needs to have similar jitter performance to the 74AC14. I use it up to 10 MHz. Best Regards Martyn ___ 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] 50 ohm Driver
Martyn -- the 74AC spec allows Vcc to go up to 6.0 VDC (absolute max is 7.0 VDC) so that might help you meet your 4.5 VDC goal, especially if this is for play and not a product. Pick the resistors and use more than 3 gates if necessary. Note the peak current spec is 50 mA per gate. Not sure what the combined gate current limit is; there is a package thermal limit. You also have to decide if you want some level of short-circuit protection or if you can always assume 50R termination. John -- have you tried long duration output shorts on the TADD-2? I figured that was also a reason for each gate having its own resistor. /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] new tdc from Texas
Hi, I've not seen any mention of anything other than the TDC1000. I was a bit surprised that they went down the less-integrated route and separated the TDC, but it turns out that for a lot of the sort of things they designed it for, a uC provides good enough timing itself, and no extra TDC is needed at all. I see that Acam have released a bit more info on their new GP30, although no data sheet yet. It quotes typical LSB of 11ps, and rms noise of 1.2 LSB, which is quite an improvement on the GP22. It would just be good if they offered a simple online way of getting low volumes of them - I suspect that the specialist distributors would be just as happy as the customers would be! Angus. On Tue, 03 Mar 2015 15:43:25 -0800, you wrote: Hi Angus: Do you know if they have an IR pulse front end which would be more interesting than the ultrasonic front end? Mail_Attachment -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html http://www.prc68.com/I/DietNutrition.html Angus wrote: In case anyone is interested, the full data sheet is on the TI site now, although I didn't see any actual IC's yet other than the ones in the eval boards. Angus. On Tue, 17 Feb 2015 21:24:08 -0200, you wrote: Initial datasheet: http://www.ti.com/lit/ds/symlink/tdc7200.pdf EVM: http://www.ti.com/tool/tdc1000-tdc7200evm Seems good... what do you think? Daniel ___ 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] 50 ohm Driver
Hi, Correct me if I'm wrong but being that AC series gates are MOS devices, isn't there inherent current limiting in the MOS junction itself? I would think that for the few nanoseconds of skew across gates the tens of ohms of junction resistance would make 'shoot through' negligible in terms of heating and gate damage. Of course, a TTL device would be a completely different story and I would fully expect summing or balancing resistor would be needed there. Does anyone have further input regarding paralleling MOS logic devices? Dan One comment on the parallel AC gate approach. It may not be directly applicable to Martyn's issue, but there is a common confusion about the value of the summing resistors. Per Tom Clark, who came up with the idea, they are*not* intended to provide a near-end line termination to 50 ohms, but are simply there to protect the paralleled devices if the gates have slightly different delays (in which case one gate could end up sinking the other two). So, the commonly used 47 ohm value isn't magic. You can use a lower value, and thus get more voltage at the far end. I haven't experimented to see how far you can take that idea before destroying gates. John ___ 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] Trimble Thunderbolt NMEA ?
The code is in C and Silabs has small dev kits (Toolsticks) that cost $10 to which you need to add $18 for the programming dongle. A little more expensive than an Arduino, or less, depending on where you buy it... To that you need to add a MAX232 (or two serial-TTL adapters at $4 each or so on ebay) and you are in business. Total cost about the same as a dedicated GPS receiver with antenna and NMEA output. Choose your poison :) Didier KO4BB On March 3, 2015 10:23:56 PM CST, Chris Albertson albertson.ch...@gmail.com wrote: Is the code in C? If so I bet it would run on some development board. No need to make custom PCBs. On Tue, Mar 3, 2015 at 5:00 AM, Didier Juges shali...@gmail.com wrote: Tim, It shouldn't be too hard to modify the code for my Thunderbolt monitor to make it into a TSIP-NMEA converter. The last version of the kit has a uC with two serial ports. I m out of the kits at the moment but I have a few spare boards left over. -- Chris Albertson Redondo Beach, California ___ 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] 50 ohm Driver
Hi If you want to drive out of a 50 ohm source into your 50 ohm load *and* get 5V into the load … that’s a fancy amp. 10V power and some careful work to get it going. If you just want to get roughly 5V into a 50 ohm load, then it’s a matter of how many gates you decide to parallel. If you go with “32 ma” drivers, you should be able to get it done with 8 of them in parallel. Drive them all off of a single dedicated fast gate that’s on the same supply. Probably best to stuff a 20 or 30 ohm resistor in series with each of the outputs. If it’s *got* to be a full 5V, don’t use the resistors. Bob On Mar 4, 2015, at 5:26 AM, Martyn Smith mar...@ptsyst.com wrote: Hello, A quick question. My output driver for a simple amplifier. I use three gates (in parallel with resistors) from a 74AC14 to give me about 0-3.2V into 50 ohm. I want to have a driver that gives me a full 0-5V (at least 0-4.5V) swing into 50 ohms. Can anyone recommend an IC that can delivery this. But it needs to have similar jitter performance to the 74AC14. I use it up to 10 MHz. Best Regards Martyn ___ 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] 50 ohm Driver
j...@febo.com said: Per Tom Clark, who came up with the idea, they are *not* intended to provide a near-end line termination to 50 ohms, but are simply there to protect the paralleled devices if the gates have slightly different delays (in which case one gate could end up sinking the other two). Is that a real problem? How far off can the prop delay be for 2 gates on the same chip? I seem to remember reading something saying it was OK to just wire them up in parallel. It could have been an app note, or it could have been a rumor on usenet. -- 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] 50 ohm Driver
Is [one gate sourcing or sinking current into paralleled gates that don't switch at exactly the same time] a real problem? How far off can the prop delay be for 2 gates on the same chip? I seem to remember reading something saying it was OK to just wire them up in parallel. It could have been an app note, or it could have been a rumor on usenet. Most manufacturers sanction direct paralleling of gates on the same chip (and forbid any paralleling, ballasted or otherwise, of outputs from different chips). However, there are other considerations (short-circuit protection, maximum output current rating per gate, maximum supply and/or ground current rating per package, maximum power dissipation, etc.). Good design practice is to put series resistors on each gate output that will prevent any of these ratings from being exceeded into a short circuit to ground or to Vcc. For HC, AC, NC7NZ, and NC7SZ, the per-gate output current rating is +/- 24 (or 25) mA, which suggests that each gate should have a 200 ohm series resistor -- but you need to check all of the other ratings mentioned above for the chip you use, to make sure they won't be violated. Unfortunately, if the load is 50 ohms to ground, pulling it to even 4.5v from a 5v logic supply requires a source resistance of only 5.6 ohms, or 36 parallel gates each with 200 ohms in series (this assumes that the gates can pull all the way to 5v while delivering rated current, which they can't -- so the reality is even worse). You can make things a little better by terminating the output into 50 ohms to 1/2 Vcc (i.e, the center of a voltage divider with 100 ohms to Vcc and 100 ohms to ground), but (i) it only gets a little better, and (ii) now it won't pull all the way to ground. All that said, why do you want to generate a high-current square wave, anyway? If you're distributing a frequency standard, it is much better to distribute a sine wave (you don't have to worry about the harmonics being skewed, and there is exponentially less of a problem with it radiating and getting into every radio and other sensitive electronic device in your house and the other houses on the block). 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] new tdc from Texas
In message blu170-w50577ecf0b24fa2bcefc50ce...@phx.gbl, Mark Sims writes: Sparkfun is selling a board (around $15) based on the STM VL6180 chip that measures distance based upon time-of-flight of pulses from an on chip (or at least in-package) VCSEL IR laser. Claims to have a range of 0 .. maybe 30 cm. Unfortunately it doesn't look like you can directly access the time interval measurement portion of the chip. It doesn't measure time interval, it measures frequency. These devices contain an oscillator where the flight of the light pulse is the delay element, then measure the resulting frequency. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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] 50 ohm Driver
Hello, A quick question. My output driver for a simple amplifier. I use three gates (in parallel with resistors) from a 74AC14 to give me about 0-3.2V into 50 ohm. I want to have a driver that gives me a full 0-5V (at least 0-4.5V) swing into 50 ohms. Can anyone recommend an IC that can delivery this. But it needs to have similar jitter performance to the 74AC14. I use it up to 10 MHz. Best Regards Martyn ___ 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.
