[SI-LIST] Re: signal source distribution and jitter question
- From: "Lewandowski, Bob" <blewandowski@xxxxxxxxxxxxxxxxxxxx>
- To: <deibele@xxxxxxx>, "Si-List Si-List" <si-list@xxxxxxxxxxxxx>
- Date: Fri, 15 Nov 2002 12:44:49 -0600
One of the problems you will have is measuring the jitter on the low
frequency signals. Amplitude noise and trigger jitter in the scope will
give you more than 5 pS on the 2.5 MHz signal. It's axis crossing rate
is only 0.3% of the 800 MHz signal, and 5 pS is 4.5 milli degrees of
phase at 2.5 MHz. Ouch!
One method to generate the signals would be to use a low phase noise
reference signal at 50 MHz, and narrow band PLLs using low noise, narrow
tuning range, VCOs, with a divider in each loop to give the appropriate
multiplication factor. Then you could use a digital divider from the 50
MHz signal to generate 2.5 MHz, and low pass filter the output to get a
clean sine wave. You could use 3 loops, and generate the 400 MHz by
dividing the output of the 800 MHz loop by 2, and then filtering.=20
Are you concerned about absolute phase stability, including long term
phase wander due to thermal effects, etc., or just short term jitter?=20
I have a friend that does commercial products in this area, if you're
interested contact me off line, and I can give you details.
---Bob Lewandowski
Principal Engineer
Stratos Lightwave
Northwest Technology Center
6100 - 219th St. S.W., Suite 520
Mountlake Terrace, WA 98043
Phone: (425) 672-8035 x103
FAX: (425) 672-8014
Mobile: (206) 856-1809
Email: blewandowski@xxxxxxxxxxxxxxxxxxxx=20
=20
-----Original Message-----
From: C Deibele [mailto:deibele@xxxxxxx]
Sent: Friday, November 15, 2002 7:08 AM
To: Paul Levin; Si-List Si-List
Subject: [SI-LIST] Re: signal source distribution and jitter question
Paul,
I need all the freqs at the same time.
5 psec jitter means that if one examines the rising edge of a particular
source
and examines the rising edge of any other source in the same
distribution, one will
not see the riding edge move by more than a certain amount.
In essence, I am interested in the RMS jitter, but that implies that
that the peak
to peak jitter is also under control.
For example, I measured the jitter of some commercial sources using a
TEK scope using
several techniques. This showed me that some extra frequency spectrum
leaked through
and this caused circa 50% of the jitter!
This topic is really a mix of SI and of good oscillator design...so I
was hoping someone
had to tackle this problem.
The only way I can solve this problem with a commercial oscillator is at
the high frequency
end -- here I measure less than a picosecond of jitter. In phase, this
shows a 0.5 degrees
of RMS jitter. Which is about accurate to 0.3%.
At the low end, Cypris makes a good chip that can do about 5
psecs...which is tolerable.
I am just curious if anything else is out there that I might try.
Thanks,
Craig
Paul Levin wrote:
> Dear Craig,
>=20
> Do you need all of these frequencies at the same time, or just a few
of
> them at any given time? What do you mean by 5 psec jitter? RMS? Peak-
> to-peak, and if so, at what probability? The answer probably lies in
> voltage controlled oscillators and phase-locked loops. By the way, how
> good a sinewave do you need?
>=20
> Regards,
>=20
> Paul
> _____________________
>=20
> C Deibele wrote:
>=20
>> 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=20
>> 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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