[SI-LIST] Re: signal source distribution and jitter question
- From: C Deibele <deibele@xxxxxxx>
- To: Bill Dempsey <BDempsey@xxxxxxxxxxxx>,Si-List Si-List <si-list@xxxxxxxxxxxxx>
- Date: Fri, 15 Nov 2002 11:09:48 -0500
Bill,
I used a TEK 8000 series scope to measure the jitter...and could
measure to around 0.5 psecs of RMS. TEK claims their scope is good
to .5 psecs...
And I know that this is a tough requirement. Clean is the keyword.
I am curious if anyone has had this experience. We are even considering
using batteries as the power supply to ensure we don't get anything from
the supply getting into the system.
I've heard of crystals w/ low jitter ... sub picosecond ... and using
it as a reference. In fact, I've measured sub 3 psecs on the "peppermint
board."
So, this is pushing the limit a bit, but something has to be available.
Thanks for your comments!
Craig
Bill Dempsey wrote:
> Craig,
>
> The real issue is the spec requirement you mentioned. I would tell
> you that it's *impossible* to realize, or measure, a true <1ps jitter.
> One can derive it mathematically.
>
> You would have to design your own control loop which itself is
> susceptible to noise from all sources. And you would have to use a very
> "clean" vcxo. This is the problem.
>
> What is the real need for such a low jitter. If you said <5ps then
> you might have a chance... By the way http:/www.eagleware.com has some
> nice PLL software that can help with the whole math problem.
>
> Bill
>
> -----Original Message-----
> From: C Deibele [mailto:deibele@xxxxxxx]
> Sent: Friday, November 15, 2002 6:01 AM
> To: Bill Dempsey
> Subject: Re: [SI-LIST] signal source distribution and jitter question
>
>
> Bill,
>
> I've looked at these -- even measured them.
>
> What I've discovered is that general sources (i.e. ones that I can input
> a
> particular frequency) jitter like mad. Especially at the low frequency
> end.
>
> So, this is not a particularly good solution.
>
> I've seen some techniques using DDS's, and fracional N's...but I do not
> have
> a warm fuzzy that they can be reliable.
>
> So, I am in a bit of a question yet.
>
> Regards,
>
> Craig
>
> > Bill Dempsey wrote:
> >
> > Craig,
> >
> > Difficult problem to solve and it requires enormous thought.
> > However, you must ask yourself how you plan to measure jitter in this
> > range.
> >
> > Several good sources of info on how to measure will lead you to a
> > solution or the realization that it's nearly impossible...
> >
> > Agilent, Vectron, Raltron plus numerous others touch on this topic.
> >
> > Bill
> >
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx
> > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of C Deibele
> > Sent: Thursday, November 14, 2002 1:35 PM
> > To: Si-List Si-List
> > Subject: [SI-LIST] signal source distribution and jitter question
> >
> > Hi,
> >
> > I have a problem to solve, and am looking for a few pointers to help.
> >
> > I need to generate several frequencies and keep them locked together.
> > The frequencies need to be stable -- which is to say to keep the
> > jitter
> > of each signal minimally low...on the order of a fraction of a
> > picosecond.
> >
> > The frequencies I need to generate are the following:
> > 2.5 MHz,
> > 50 MHz,
> > 350 MHz,
> > 400 MHz,
> > 750 MHz, &
> > 800 MHz.
> >
> > I need sinusoids. I am nervous about the rather tight constraints on
> > the jitter. Most of the parts I've used are circa 5 psecs of jitter.
> > Does anyone have any pointers or perhaps a special part that can
> > handle this constraint?
> >
> > thanks,
> >
> > Craig Deibele
>
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