At this point, I have three prototype boards that are functional as far as I can tell. Unfortunately I don’t have a better reference which would allow me to make comparisons.
If someone with a better reference could make a proper comparison, I’d be happy to send them a prototype. > On Oct 22, 2016, at 1:15 PM, Scott Stobbe <scott.j.sto...@gmail.com> wrote: > > 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 <kb...@n1k.org <mailto:kb...@n1k.org>> > 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 <scott.j.sto...@gmail.com >> <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 <kb...@n1k.org >>> <mailto:kb...@n1k.org> <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 <scott.j.sto...@gmail.com >>>>> <mailto:scott.j.sto...@gmail.com> >> <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 <kb...@n1k.org >>>>> <mailto:kb...@n1k.org> <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 <scott.j.sto...@gmail.com >>>>>>> <mailto:scott.j.sto...@gmail.com> >> <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 <kb...@n1k.org >>>>>>> <mailto:kb...@n1k.org> <javascript:;> >> <javascript:;>> >>>>>> wrote: >>>>>>> >>>>>>>> Hi >>>>>>>> >>>>>>>>> On Oct 21, 2016, at 7:44 PM, Scott Stobbe < >> scott.j.sto...@gmail.com <mailto:scott.j.sto...@gmail.com> <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 < >>>>>> scott.j.sto...@gmail.com <mailto:scott.j.sto...@gmail.com> >>>>>> <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 < >>>>>> scott.j.sto...@gmail.com <mailto:scott.j.sto...@gmail.com> >>>>>> <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 < >>>>>>>>>>> time-nuts@febo.com <mailto:time-nuts@febo.com> <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 <nsa...@kfu.com >>>>>>>>>>>>> <mailto:nsa...@kfu.com> >> <javascript:;> >>>>>> <javascript:;> >>>>>>>> <javascript:;>> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>>> On Aug 30, 2016, at 8:48 PM, Cube Central < >>>> cubecent...@gmail.com <mailto:cubecent...@gmail.com> <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 -- time-nuts@febo.com <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 -- time-nuts@febo.com <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 -- time-nuts@febo.com <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 -- time-nuts@febo.com <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 -- time-nuts@febo.com <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 -- 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 <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 <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 <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 <mailto:time-nuts@febo.com> > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > <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.