RE: [SI-LIST] : Jitter Measurement

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From: Zabinski, Patrick J. ([email protected])
Date: Tue Apr 03 2001 - 09:11:24 PDT

Please excuse my ignorance and enlighten me...

I was under the impression that "noise" had both
phase and magnitude components, so the 750 uV noise
floor spec does add amplitude 'jitter' as you state.
However, isn't there an additional phase component
in there somewhere? If so, does Tek provide
this spec?

Also, regardless of the noise floor of the SD-24
head, shouldn't we be taking into account the
phase stability (a.k.a., jitter) of the reference
oscillator internal to the TEK11801? Is this where
the 2 ps spec comes in?

Again, this is a weak spot of mine, but it would seem
that you should "add" (simple add? RMS? other?) the
various jitter components together to obtain the composite jitter.



> This is not quite true. It depends on the slewrate of the
> signal being
> measured. assuming you are using the SD24 head, this has a
> noise floor
> of 750uV (can't use the averaging function when measuring jitter). Now
> if the slew rate of the signal at the jitter measuring point is say
> 2.6mV/ps (approx 500Mhz 1V p-p sinewave) then that 750uV of
> noise looks
> like 750/2600 ps of jitter but with a 1V 50MHz signal (260uV/ps
> slewrate) it would look like 750/260 ps of jitter. A similar effect
> would occur for a 0.1V 500Hhz signal. Now the same principle also
> applies to the trigger. A slow slew rate gives more trigger
> uncertainty,
> which appears as jitter.
> So get the biggest amplitude fastest risetime trigger signal you can
> and keep the Y amp attenuation to a minumum.
> Dave.
> Mike Hughes wrote:
> >
> > A while ago, a TEK apps engineer told me that the "noise
> floor" of the 11801B is
> > around 2pS RMS. My impression was that this limit is
> independent of the
> > frequency being measured. (As long as you are within the BW of the
> > scope/sampling head of course.)
> >
> > Mike

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