Re: [SI-LIST] : Jitter Measurement

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From: David Instone (david_instone@uk.xyratex.com)
Date: Tue Apr 03 2001 - 07:52:45 PDT


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
>
> Khalid Ansari wrote:
> >
> > Hi,
> >
> > For jitter measurements at 2.5GHz how accurate is a sampling scope
> > (Ex: Tek 11801 B/C) as opposed to a Time Interval Analyzer
> > (Ex: Wavecrest). How about frequencies around 100-200Mhz. In the
> > case if you don't have a TIA how acceptable are the values taken using
> > the scope. In the past I have used the scope only for approximate values.
> >
> > Thanks in advance,
> > Khalid
> > ---
> > Khalid Ansari
> > Switch Fabric Applications
> > Advanced Networking Products Division
> > Vitesse Semiconductor Corp.
> > 3408, Garrett Ave., Santa Clara, 95054
> > Phone: (408) 986-4381 x144
> > fax: (408) 986-6050
> > http://www.vitesse.com
> >
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-- 
Regards

Dave Instone. Compliance Engineer Storage Systems Development, MP24/22 Xyratex, Langstone Rd., Havant, Hampshire, P09 1SA, UK. Tel: +44 (0)23-92-496862 (direct line) Fax: +44 (0)23-92-496014 http://www.xyratex.com Tel: +44 (0)23-92-496000

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