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.
