Re: [SI-LIST] : Jitter measurement

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From: Paul Levin (levinpa@earthlink.net)
Date: Mon Mar 19 2001 - 22:03:07 PST


Mike,

I grant you that amplitude variation in the osciallator's output could
mask any jitter effects, but in single-frequency oscillators operating
from clean supplies supplies, I haven't encountered AM (amplitude
modulation) that was anything the like amount of PM (phase modu-
lation.) If this is truly a concern, and it may be for some *crystal*
oscillators, one could always use a limiter stage or two between the
oscillator and the spectrum analyzer in order to clobber the AM.

Paul

Mike Jenkins wrote:

> Paul, Sunil,
>
> Using a spectrum analyzer to measure jitter assumes that there is
> negligible variation in amplitude of the signal. I think this can
> be a very tough assumption to make valid.
>
> Regards,
> Mike
>
> Paul Levin wrote:
> >
> > Dear Sunil,
> >
> > Better than either of these would be to get your hands on a good,
> > old-fashioned analog spectrum analyzer. Center your display on
> > the nominal frequency and then decrease your resolution bandwidth
> > (and everything that goes along with it) so that you can see the
> > detail in the first few KHz on either side of the center frequency.
> >
> > You'll have to study up on jitter mathematics and dBc offsets, but
> > once you've got that straight, you can integrate the flanks of your
> > oscillator between any f1 and f2 and determine the likely jitter
> > arising from noise in that frequency range.
> >
> > Paul Levin
> > Senior Principal Engineer
> > Logic Innovations
> > __________________
> >
> > Sunil Kumar wrote:
> >
> > > Hello everybody..
> > >
> > > I want to measure cycle-to-cycle jitter generated by a crystal
> > > oscillator. I have two options:
> > >
> > > 1) Real time oscilloscope
> > > 2) Sampling oscilloscope
> > >
> > > The bandwidth of the real time oscilloscope is enough for my
> > > measurements. Both the oscilloscopes are equipped with jitter
> > > measurement packages. Can anybody suggest which method is better?
> > > And why?
> > >
> > > Thanks a lot..
> > >
> > > Sunil Kumar
> > >
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> --
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Mike Jenkins Phone: 408.433.7901 _____
> LSI Logic Corp, ms/G715 Fax: 408.433.7495 LSI|LOGIC| (R)
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