Final Report - Binary Sampler

[Mike]

Hi, Mike,

When I said the math is a bitch, I didn't mean it was hard to do,
rather that the consequences are nasty for a heterodyne timebase.

What MM's doing is using a 1 MHz oscillator to make a fast edge, and
using a separate 1.000001 MHz oscillator as the timebase trigger for a
sampler. So he's effectively sweeping 1 usec of equivalent time in 1
second of real time, theoretically at 1 ps per sample. The question I
had was the effect of oscillator phase noise in such a situation,
especially using non-ovenized oscillators. A simple XO will typically
accumulate about 1 ns error per second, often worse, so his timebase
will jitter about like that. But a single 200 ps edge is swept in 200
usec of real time, and the jitter *during* that single edge won't be
bad. Of course, that edge will effectively wobble and wander around in
time on successive sweeps.

Yup, that's the problem, but you'll never convince Mike. After all these
exchanges, I'm not even sure he understands the issues that have been
raised. This exchange hasn't done anything to assuage that opinion.

When MM says "24.7ps over 10 seconds" I think he's actually measuring
cycle-to-cycle jitter, but taking 10 seconds to make the ensemble
measurement. That's a whale different from using the same oscillator
to time a 10-second period, and measuring the jitter of *that*. No
simple oscillator is going to be steady to a couple parts in 1e12 over
10 seconds.

That's what I think too. I suspect that if he was to divide by 1 million
and measure the divider output, he'd find quite a different result.

-- Mike --