I think we are coming up to the noise floor here. We have identified a potential signal A from a 7912 (likely similar to a 7812, no guarentee). The remaining question is if you apply signal A to the power pin of a thunderbolt what is signal B added to the output. We know where we want signal B to be, below the noise. Knowing the PSSR for each of the power inputs would be one way to answer this question.
On Saturday, 22 October 2016, Bob Camp <[email protected]> wrote: > Hi > > There is an *enormous* difference between regulation and it’s impact on > stability (which is what this drifted off into) and PSRR and it’s impact on > phase noise (which got lost at the tread moved on). PSRR does indeed > matter, but a fairly simple linear regulator (or pair of cheap ones or > coil plus > pair) can take care of that. > > The EFC reference in the TBolt comes from the TBolt board and not from the > OCXO. > It is not in any way connected to the -12 V supply line. > > Bob > > > > > On Oct 22, 2016, at 12:41 PM, Scott Stobbe <[email protected] > <javascript:;>> wrote: > > > > Bob, this is good data and insights thanks for taking the time to share. > > Ultimately the question Nick is hoping to answer is what is the point of > > diminishing returns for voltage regulation. I think there are plenty of > > folks on this list that have shared data suggesting a switching regulator > > which meets these specifications: > > > > Table 3-2 Power Specifications (Board-only) > > +12v +/-10% max current 750 mA > > +5v +/-5% max current 400 mA > > -12v +/-10% max current 10 mA > > Ripple > > +5v 50 mV peak-to-peak, 15 mVrms > > +/-12v 75 mV peak-to-peak, 20 mVrms > > > > definitely has a degrading impact on the 10MHz phase noise. > > > > I would happily agree that PSRR of an opamp buffering the EFC line is not > > going to have a significant impact on performance with a jellybean LDO. > > > > Do you know if the +- 5V reference is derived on board or is it from an > EFC > > reference provided by the ocxo? > > > > On Sat, Oct 22, 2016 at 11:31 AM, Bob Camp <[email protected] <javascript:;>> > wrote: > > > >> Hi > >> > >> The -12 V line is not the reference for the EFC. It *is* one supply into > >> the op amp circuit > >> that drives the EFC. Since the EFC is +/- 5V, there must be both a > >> positive and > >> a negative supply into the driver circuit for full output swing. The -12 > >> can be anything between about > >> -13 and -7 without significantly impacting the function of the device. > In > >> fact, people > >> with EFC voltages that are slightly positive have accidentally proven > that > >> the > >> TBolt will work (lock up and function correctly) with zero volts on the > >> -12V line. > >> > >> Bob > >> > >>> On Oct 22, 2016, at 10:24 AM, Scott Stobbe <[email protected] > <javascript:;>> > >> wrote: > >>> > >>> It all depends what the -12V rail is for, some have said it directly > >>> references the EFC dac. I would hope an ocxo would have a better tuning > >>> gain on its efc pin than supply pin but maybe that's not always true. > >>> > >>> On Saturday, 22 October 2016, Bob Camp <[email protected] <javascript:;>> > wrote: > >>> > >>>> Hi > >>>> > >>>> The +12 goes straight to the OCXO. All OCXO’s have a voltage > >> sensitivity. > >>>> That sensitivity is much higher than voltage sensitivity is much > higher > >>>> than > >>>> what you see on the other two supply pins. > >>>> > >>>> Bob > >>>> > >>>>> On Oct 21, 2016, at 11:06 PM, Scott Stobbe <[email protected] > <javascript:;> > >>>> <javascript:;>> wrote: > >>>>> > >>>>> Interesting, I would have thought that the +12V input would be > >> extremely > >>>>> well regulated since its shared with the oven heater, I*R drops are > >> going > >>>>> to show up every where, if your looking for uV levels of stability. > >>>>> Just a connector has milliohms of contact resistance, let alone > routing > >>>> and > >>>>> cables... > >>>>> > >>>>> On Friday, 21 October 2016, Bob Camp <[email protected] <javascript:;> > <javascript:;>> > >>>> wrote: > >>>>> > >>>>>> Hi > >>>>>> > >>>>>>> On Oct 21, 2016, at 7:44 PM, Scott Stobbe < > [email protected] <javascript:;> > >>>> <javascript:;> > >>>>>> <javascript:;>> wrote: > >>>>>>> > >>>>>>> A little more data on the 7912. > >>>>>>> > >>>>>>> The first plot shows the tempCo of the 7912 measured with ambient > >>>>>>> temperature swings "7912_TempCo.png". Which is -150 ppm/degC. > >>>>>>> > >>>>>>> The second plot is off a 7912 logged for an hour or so, > >>>> "7912_1PLC.png", > >>>>>>> nothing too interesting here. However the environmental temperature > >>>> swing > >>>>>>> of about 1 degC/hour is pretty conservative for a DUT sitting in > free > >>>>>> air. > >>>>>>> > >>>>>>> Finally, an allan devation plot looking at the normalized stability > >> of > >>>> a > >>>>>>> 7912 regulator "7912_AllanDeviation.png". Interestingly here, is, > how > >>>>>> quick > >>>>>>> a 15 mK/min temperature swing shoots above the 1/f floor, it's a > >> matter > >>>>>> of > >>>>>>> seconds. > >>>>>>> > >>>>>>> Now if your PSRR is 1 ppb/V or better, then all of this is > >> comfortably > >>>>>>> below the intrinsic noise of a thunderbolt. > >>>>>> > >>>>>> The main point is that the internal tempco of the TBolt it’s self is > >>>> much > >>>>>> larger than > >>>>>> the issues surrounding the power supply pins. The +12 is the only > one > >>>> that > >>>>>> is > >>>>>> sensitive enough to voltage (change in frequency vs voltage) to > >>>> contribute > >>>>>> to any > >>>>>> significant way to the overall stability. > >>>>>> > >>>>>> Bob > >>>>>> > >>>>>>> > >>>>>>> On Fri, Oct 21, 2016 at 12:20 AM, Scott Stobbe < > >>>> [email protected] <javascript:;> <javascript:;> > >>>>>> <javascript:;>> > >>>>>>> wrote: > >>>>>>> > >>>>>>>> Nick had mention that the -12V rail on the thunderbolt has the > >> poorest > >>>>>>>> PSRR with respect to frequency output, so I first took a look at > the > >>>>>>>> venerable 7912. > >>>>>>>> > >>>>>>>> The first data-set was taken with a -13.5 VDC input. Attached is > the > >>>> 0.1 > >>>>>>>> Hz to 10 Hz noise of an essentially quiescently loaded 7912, only > a > >>>> 10k > >>>>>>>> resistor was added as load for preliminary evaluation. With a 60 > dB > >>>>>> preamp > >>>>>>>> the scale of the scope plot is 20 uV/div. The 0.1Hz to 10Hz band > >> noise > >>>>>> is > >>>>>>>> 15 uVrms, which is about 1.3 ppm rms of the DC mean. > >>>>>>>> > >>>>>>>> In allan deviation terms, a quiescently loaded 7912 has a spot > noise > >>>> of > >>>>>> 7 > >>>>>>>> uV/rtHz at 1 Hz (on the 1/f slope), normalized that's 580 > ppb/rtHz. > >>>>>>>> Equivalently speaking, the flicker noise floor of an allan > deviation > >>>>>> plot > >>>>>>>> would be sqrt(2*ln(2)) that figure to be 6.8E-7. > >>>>>>>> > >>>>>>>> Assuming a thunderbolt should be achieving 1/f floor of around > >> 1E-12, > >>>> it > >>>>>>>> would need a PSRR of at least 1 ppm/V. I'm sure someone has gone > to > >>>> the > >>>>>>>> trouble of actually measuring it. > >>>>>>>> > >>>>>>>> So from a 0.1 Hz to 10 Hz noise standpoint, the 7912 isn't > terrible > >>>>>>>> with 1.3 ppm rms noise, considering an LM399 is about 0.1 ppm rms, > >>>> only > >>>>>> one > >>>>>>>> order of magnitude off. > >>>>>>>> > >>>>>>>> The bad side of a 7912 is in long-term stability and tempCo, the > >>>> sample > >>>>>> I > >>>>>>>> tested had at least a 150 ppm/degC tempCo, which is going to put a > >>>>>> serious > >>>>>>>> lump/bump in the 10s tau to gps crossover point on an allan > >> deviation > >>>>>> plot. > >>>>>>>> > >>>>>>>> > >>>>>>>> > >>>>>>>> On Tue, Oct 18, 2016 at 3:05 PM, Scott Stobbe < > >>>> [email protected] <javascript:;> <javascript:;> > >>>>>> <javascript:;>> > >>>>>>>> wrote: > >>>>>>>> > >>>>>>>>> I'm sure I have some 7805s lying around, maybe a 7812/7912. I'm > >>>>>>>>> interested to see the 1/f noise of a classic regulator, what load > >>>>>> current > >>>>>>>>> do you expect? I can bias a 7805 for the same load and measure > the > >>>> 0.1 > >>>>>> to > >>>>>>>>> 10 Hz noise. > >>>>>>>>> > >>>>>>>>> Also if you have a digital scope without a very good builtin FFT, > >>>>>> octave > >>>>>>>>> would be one solution. > >>>>>>>>> > >>>>>>>>> On Tue, Oct 18, 2016 at 10:46 AM, Nick Sayer via time-nuts < > >>>>>>>>> [email protected] <javascript:;> <javascript:;> > <javascript:;>> wrote: > >>>>>>>>> > >>>>>>>>>> Just an update. I’ve built the second prototype board (I skipped > >>>> over > >>>>>>>>>> the first design), and it’s powering my tbolt right now. > >>>>>>>>>> > >>>>>>>>>> The design calls for 15v in (though it would also work with > >> 13.8v). > >>>>>> The > >>>>>>>>>> +12 output comes from a D2PAK 7812. For +5, there is an AP1509 > >> buck > >>>>>>>>>> converter to make around 6.5 volts, then a DPAK 7805. For -12, > >> there > >>>>>> is an > >>>>>>>>>> MC34063 configured as an inverter to make around -13.75 volts > and > >>>>>> then a > >>>>>>>>>> DPAK 7912. > >>>>>>>>>> > >>>>>>>>>> Steady-state, the system appears to be working just fine. The > >>>> AP1509’s > >>>>>>>>>> inductor and the D2PAK 7812 are just warm to the touch. > >>>>>>>>>> > >>>>>>>>>> I checked for noise and ripple on the outputs and it’s somewhere > >>>>>> around > >>>>>>>>>> ±2 mV or so generally. From what I can see on the scope, there’s > >> no > >>>>>> ripple > >>>>>>>>>> - it’s all high frequency noise. I am not absolutely certain > that > >>>> the > >>>>>> noise > >>>>>>>>>> measurement represents real noise or the limits of my measuring > >>>>>> ability. > >>>>>>>>>> I’m just using the scope probes the scope came with, and 2 > mV/div > >> is > >>>>>> its > >>>>>>>>>> lowest range. > >>>>>>>>>> > >>>>>>>>>> I haven’t compared the noise with the ex laptop supply that I > was > >>>>>> using > >>>>>>>>>> before, but I’d have to believe it’s cleaner. I don’t really > have > >> a > >>>>>> way to > >>>>>>>>>> check the oscillator’s before and after ADEV. My only other > >>>> reference > >>>>>> is an > >>>>>>>>>> FE5680A, and I think the thunderbolt’s going to be far better at > >>>>>> lower tau > >>>>>>>>>> (where this all matters). > >>>>>>>>>> > >>>>>>>>>> I know also that ±2 mV is still one and perhaps two orders of > >>>>>> magnitude > >>>>>>>>>> higher than some have called for. But before I attempt to reduce > >> the > >>>>>> noise > >>>>>>>>>> further, I’d like to know that there are real gains to be had. > >> Would > >>>>>>>>>> someone with a Thunderbolt and better output noise measuring > >>>>>> wherewithal be > >>>>>>>>>> willing to take a prototype and compare it with something that > >> does > >>>>>> have µV > >>>>>>>>>> levels of noise and ripple so I can get an idea of what there is > >> to > >>>>>> gain? > >>>>>>>>>> If you like, you can make such comparisons public - no secrets > >> here. > >>>>>>>>>> > >>>>>>>>>>> On Aug 30, 2016, at 10:37 PM, Nick Sayer <[email protected] > <javascript:;> > >>>> <javascript:;> > >>>>>> <javascript:;>> wrote: > >>>>>>>>>>> > >>>>>>>>>>> > >>>>>>>>>>>> On Aug 30, 2016, at 8:48 PM, Cube Central < > >> [email protected] <javascript:;> > >>>> <javascript:;> > >>>>>> <javascript:;>> > >>>>>>>>>> wrote: > >>>>>>>>>>>> > >>>>>>>>>>>> I would be interested, I think. Planning ahead for if the > one I > >>>>>> have > >>>>>>>>>> for my Thunderbolt fails, I guess. Are there different models > or > >>>>>> would a > >>>>>>>>>> photo of the input ports on mine be useful? > >>>>>>>>>>> > >>>>>>>>>>> Actually, what I had in mind is to just put a SIP4 header on > the > >>>>>> board > >>>>>>>>>> for the output and people could wire the “last mile” themselves. > >> The > >>>>>> input > >>>>>>>>>> is a 2.1mm barrel connector. You use whatever 15W 12VDC wall > wart > >> is > >>>>>> handy > >>>>>>>>>> and plug it right in. > >>>>>>>>>>> > >>>>>>>>>>> What it really amounts to is that you get +12 volts directly > from > >>>> the > >>>>>>>>>> input, then there’s a buck converter to drop the +12 down to +5 > >> and > >>>> an > >>>>>>>>>> inverter to generate -12 from the +12. Those 3 voltages, plus a > >>>>>> ground go > >>>>>>>>>> to the SIP4. > >>>>>>>>>>> > >>>>>>>>>>> So it’s just two switching power supplies to turn a +12 volt > only > >>>>>>>>>> supply into the three-way that the Thunderbolt wants. > >>>>>>>>>>> > >>>>>>>>>>> It’d be good for around 1500 mA @ 5V and around 50 mA @ -12 > (the > >>>> +12 > >>>>>>>>>> spec is whatever is left from the source supply’s power spec) - > >> more > >>>>>> than > >>>>>>>>>> enough for a Thunderbolt. Probably enough for a hard disk or a > >>>>>> smallish PC. > >>>>>>>>>> _______________________________________________ > >>>>>>>>>> time-nuts mailing list -- [email protected] <javascript:;> > <javascript:;> > >>>> <javascript:;> > >>>>>>>>>> To unsubscribe, go to https://www.febo.com/cgi-bin/m > >>>>>>>>>> ailman/listinfo/time-nuts > >>>>>>>>>> and follow the instructions there. > >>>>>>>>>> > >>>>>>>>> > >>>>>>>>> > >>>>>>>> > >>>>>>> <7912_1PLC.png><7912_AllanDeviation.png><7912_ > >>>>>> TempCo.png>_______________________________________________ > >>>>>>> time-nuts mailing list -- [email protected] <javascript:;> > <javascript:;> > >>>> <javascript:;> > >>>>>>> To unsubscribe, go to https://www.febo.com/cgi-bin/ > >>>>>> mailman/listinfo/time-nuts > >>>>>>> and follow the instructions there. > >>>>>> > >>>>>> _______________________________________________ > >>>>>> time-nuts mailing list -- [email protected] <javascript:;> > <javascript:;> > >>>> <javascript:;> > >>>>>> To unsubscribe, go to https://www.febo.com/cgi-bin/ > >>>>>> mailman/listinfo/time-nuts > >>>>>> and follow the instructions there. > >>>>>> > >>>>> _______________________________________________ > >>>>> time-nuts mailing list -- [email protected] <javascript:;> > <javascript:;> > >>>>> To unsubscribe, go to https://www.febo.com/cgi-bin/ > >>>> mailman/listinfo/time-nuts > >>>>> and follow the instructions there. > >>>> > >>>> _______________________________________________ > >>>> time-nuts mailing list -- [email protected] <javascript:;> > <javascript:;> > >>>> To unsubscribe, go to https://www.febo.com/cgi-bin/ > >>>> mailman/listinfo/time-nuts > >>>> and follow the instructions there. > >>>> > >>> _______________________________________________ > >>> time-nuts mailing list -- [email protected] <javascript:;> > >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ > >> mailman/listinfo/time-nuts > >>> and follow the instructions there. > >> > >> _______________________________________________ > >> time-nuts mailing list -- [email protected] <javascript:;> > >> To unsubscribe, go to https://www.febo.com/cgi-bin/ > >> mailman/listinfo/time-nuts > >> and follow the instructions there. > >> > > _______________________________________________ > > time-nuts mailing list -- [email protected] <javascript:;> > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] <javascript:;> > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
