Hi Coming up with a reference clock can be harder than you might think.
Most of the jitter numbers you see published on frequency sources are based on a “jitter mask” that runs from (maybe) 10 KHz up to 20 MHz. That’s fine for a specific telecom need. It may not in any way apply to capturing a 1 pps pulse. *IF* you believe the phase noise to jitter integration stuff (and there are reasons not to) the jitter goes way up as you integrate closer to carrier. A 0.1 ps source can quickly turn into a 10 or 100 ps source with a change of the lower bound on the jitter mask. Now, once you have the jitter number, you are only part way to knowing it’s impact on your measurement. There are *always* more things to consider. Bob > On Jun 15, 2015, at 6:14 PM, Attila Kinali <att...@kinali.ch> wrote: > > On Thu, 11 Jun 2015 14:22:58 +0000 > Alan Ambrose <alan.ambr...@anagram.net> wrote: > >> A clever interpolator for frequency or TIC would kill it - >> for TIC essentially a PICTIC on steroids. The PICTIC does 19pS with >> a 10 bit ADC and a 66MHz clock, an SR620 does 4pS with a 12 bit ADC >> and an 80 MHz clock - so ... cough ... Spartan 3E at 256MHz with 16 >> bit ADC - and 1pS should be easy > > Which architecture for the FPGA do you have in mind? The delay > line method (which is the most common one for FPGAs) has an intrinsic > limit around 10-20ps. But the SR620 and the PICTIC use both a time to > amplitude > conversion by charging a capacitor (both include a Nutt interpolator). > > Using this technique, it might be possible to get into the 1ps ballpark, > if the design is done carefully (according to Richard McCorkle, the > limiting factor for the PICTIC II was the ADC of the PIC, followed by > the stability of the reference clock). > > Attila Kinali > > -- > I must not become metastable. > Metastability is the mind-killer. > Metastability is the little-death that brings total obliteration. > I will face my metastability. > I will permit it to pass over me and through me. > And when it has gone past I will turn the inner eye to see its path. > Where the metastability has gone there will be nothing. Only I will remain. > > _______________________________________________ > 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.