[time-nuts] Updated Divider Jitter Results - 74HC390

John Ackermann N8UR jra at febo.com
Sun Apr 5 00:09:28 UTC 2009


Bruce Griffiths said the following on 04/04/2009 07:30 PM:
> John
> 
> I can't find a spec for the Wavecrest 2075 input amplifier/trigger
> circuit noise but it could be as high as 1mV rms given its 800MHz+ input
> bandwidth.
> 
> If the noise is 1mV rms:
> Then an input signal slew rate of 1V/ns is required to keep the jitter
> contribution of the amplifier input noise below 1ps rms.
> A 3 stage limiter cascade with an overall slope gain of about 12x can be
> used to increase the slew rate of a 10MHz 2V pp input signal to 1V/ns.
> With an appropriate distribution of limiter stage gain and bandwidth,
> the jitter contribution due to limiter noise and Wavecrest input noise
> can be held below1.2ps rms.
> The jitter contribution due to amplifier input noise with such an input
> signal connected directly to the Wavecrest input would be about 16ps rms.

Bruce --

A simple experiment just verified your hunch that input amp noise is a
limiting factor.  Using the Wavecrest in time interval ("total
propagation delay") mode with signal going into channel 1, then through
a 4 foot cable into channel 2 to generate about 6 ns of delay (with a
tee at channel 2 providing a 50 ohm load):

A 10 MHz sine wave at 1.0V P-P shows a 100K sample jitter of 23 ps.

A 10 MHz pulse train at 1.0V P-P from a 5359A Time Synthesizer (with < 5
ns transition time) shows a 100K sample jitter of 4 ps.

I think I missed the point of your suggestion a couple of messages ago,
but I get it now -- to measure the input circuit performance, I probably
need to use two input circuits, one fed to start and the other to stop,
so the Wavecrest can get a better slew rate to deal with, then divide by
sqrt(2).  That'll be part of tomorrow's experiments...

John




More information about the time-nuts mailing list