Hi Simple test:
1) Run sine wave into a power splitter 2) Run one port to your limiter / zero crossing detector / what ever 3) Run other port from the power splitter into the "reference" port on a DTMD, 5125, or (better yet) TimePod. 4) Route the output of the limiter to the "input" port on the instrument. You may need to convert it back to a sine wave for some of the above gear. What you read on the instrument will be the jitter added by the detector. None of them use a comparator on the input. Bob On Jul 20, 2012, at 6:09 PM, Azelio Boriani wrote: > OK, very interesting. Now is it possible to measure/verify this? I think > that using any test equipment, the comparator-style approach is > unavoidable: the trigger of the scope or the counter cannot be an > amplifier/limiter. How to tell what is up to my design under test and what > is the trigger contribution? Maybe only by comparison: test design A then > design B and see which is better... > > On Fri, Jul 20, 2012 at 2:31 PM, Magnus Danielson < > mag...@rubidium.dyndns.org> wrote: > >> On 07/20/2012 07:42 AM, Chris Albertson wrote: >> >>> On Thu, Jul 19, 2012 at 5:47 PM, Rick Karlquist<rich...@karlquist.com> >>> wrote: >>> >>> >>>> Hysteresis does nothing to eliminate jitter or temperature >>>> >>> >>> Maybe, but it is absolutely needed if there is any noise on the >>> signal. A perfect comparator with zero hysteresis would dither on >>> every zero crossing. >>> >> >> Yes, and this dither is due to the additive noise on the signal. The >> slew-rate at and about the trigger point will determine how much of that >> additive noise is converted into time-noise. The schmitt trigger is there >> to make sure that you surpress the dither around each transition, but it >> will not help you to remove the time polution, as the first time the dither >> occurs, is bound to be early and bound to be controlled by the noise. >> Those, the noise will shift the trigger point. >> >> You can view the schmitt trigger detector as having a state, and when in >> proximity of the trigger point, you let the noise control when the trigger >> point occurs. >> >> If you noise is pure gaussian noise, this is not so bad, since the trigger >> point will be shifted by the noise RMS, but it will be noisy. >> If you have say a sine signal, then the non-linearity of the trigger point >> will act like a mixer and it will cause the time jitter to be spread out, >> and the peak-to-peak amplitude of the signal will when divided by the >> slew-rate of the trigger point convert to the peak-to-peak time modulation >> at that frequency. The distribution has a very steep bath-tub look, since >> the sine spend most of it times at its extremes (where it's slew-rates are >> low) but very little time in the middle (where it's slew-rate are high). >> The sine signal would modulate the trigger point up and down on the slope >> it's at. The schmitt trigger action doesn't help to protect this behaviour. >> >> Schmitt trigger is a nice tool, but it can do you great harm if you do not >> understand what it does help you with and what it doesn't help you with. >> >> You need to gain yourself to slew-rates where a schmitt trigger would do >> no harm, and when you are there it will do essentially no good either, as >> you are looking at a high slew-rate square signal. >> >> So, you *can* do better than a Schmitt trigger. A schmitt trigger can be >> sufficiently good. A schmitt trigger can work well if you have filtering in >> front of it to significantly reduce unwanted systematic noise. >> >> Cheers, >> Magnus >> >> _______________________________________________ >> 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. _______________________________________________ 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.