Hi There are a lot of different 78x05 devices out there and various outfits pay more or less attention to the tempco on various die shrinks / redesigns. You can see a *wide* range of temperature performance ( > 10:1) between different examples from vendor A vs vendor B.
With any linear regulator, self heating can degrade the “input side” rejection. Since there are lots of ways to load a regulator, this just piles in on top of the tempco stuff. If the 74AC04 *is* the dominant source of error (and I’m not at all sure it is), there are chips with significantly lower propagation delay. Has your 74AC04 been through a shrink that cuts it’s delay in half? Who knows …. Who’s “king of the hill” this month? Buy a bunch of chips and test them. It all gets really tangled …... Bob > On Jan 8, 2022, at 2:41 AM, Bruce Griffiths <[email protected]> > wrote: > > Tom > > The voltage coefficient of delay for a 74AC04 is around -300ps/V so with a > tempco of -1.1mV/k for the output of a 7805 this results in an induced delay > tempco of around +0.33ps/K for the 74AC04 due to the voltage regulator > tempco. The typical propagation delay of the 74AC04 is around 4ns with an > associated tempco of around 12ps/K. Thus the actual propagation tempco > dominates over induced tempco. I would expect a similar result for the PIC > clock to output propagation delay. > > Bruce >> On 08/01/2022 16:05 Tom Van Baak <[email protected]> wrote: >> >> >> All -- The 2012 test results for the T2-mini, which contains a PIC >> divider chip, is here: >> >> http://leapsecond.com/pic/jitter/ >> >> It's about 1 ps, or sqrt(2) less because it was comparing two T2-mini >> against each other with a common reference. Also note that this >> measurement is the sum total of the Wenzel sine-to-square circuit >> onboard the T2mini, the PIC divider chip itself, and the 74AC04 buffer chip. >> >> I also included some plots of a baseline test to show that the Wenzel >> ULN (Ultra Low Noise) reference and the Miles' TimePod analyzer are not >> the limiting factor in the test. >> >> Hal -- The pD17 PIC divider used in the T2-mini has a single output. See >> T2-mini schematic in the above URL. The PIC code is here: >> >> http://leapsecond.com/pic/src/pd17.asm >> >> Bruce -- I agree with your comments. Thanks for posting that. >> >> Attila -- I have not measured the voltco. Note the T2-mini has an >> onboard regulator. I also have not measured tempco. Although the jitter >> is about 1 ps the wander over that 10 minute run is about ±6 ps (2.4 ps >> rms). Look at the phase plot in the test results. This is also why the >> ADEV plot has that characteristic plateau from tau 2 to 20 s. >> >> IIRC, the test was done causally on a floor in open air so walking, >> breathing, drinking coffee, and checking email are known to wiggle >> things at the picosecond level. Someone could look into this more if >> they wish. I would be interested to know how much of the wandering is >> due to the voltage regulator vs. Wenzel transistor circuit vs. the PIC >> vs. the 74AC chip. >> >> /tvb >> >> >> On 1/7/2022 12:40 PM, Hal Murray wrote: >>>> The two biggest outside influences on the PICDIV are supply voltage and >>>> temperature. >>> Another interesting influence is the number of outputs that are switching >>> and >>> the load on them. In particular, if you have several outputs running at >>> different frequencies, the clock-out delay should be slightly longer when 2 >>> outputs switch when compared to when only one is switching. >>> >>> Has anybody measured that on a PIC? (or similar chip) >>> >>> I think one of tvb's picDEVs has several outputs. >>> >> >> On 1/7/2022 5:00 PM, Bruce Griffiths wrote: >>> That entire thread is full of misinformation and should be ignored unless >>> one understands the difference between random and data dependent jitter. >>> >>> For a well designed divider with a single output frequency only the random >>> jitter spec is significant. >>> >>> One doesn't need a bunch of expensive LeCroy gear to measure RJ of such >>> dividers as its PN manifestations are readily apparent and measurable. >>> >>> Using one of the supposedly super low jitter flipflops isn't a panacea. In >>> practice unless an appropriately designed ZCD is used the wideband input >>> noise of the very fast FF will dominate and produce much more jitter than >>> expected due to the relatively slow slew rate of the outputs of most 10MHz >>> sources. >>> >>> Bruce >> _______________________________________________ >> time-nuts mailing list -- [email protected] -- To unsubscribe send an >> email to [email protected] >> To unsubscribe, go to and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send an > email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
