1pSec Jitter

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
Hi All,

I have a FPGA system which requres better than 1pSec jitter.

When I ask the Xtal MFG they advise there are 2 methods of measuring Jitter
Peak to Peak and an averaging method

Measuring the same Xtal the result can be significatly differment values
between the 2 methods.

Does any one have any information on the 2 methods (or more) how to measure
jitter.

What would FPGA input expect?

Regards
JG



Re: 1pSec Jitter
Quoted text here. Click to load it

What do you mean by 1 psec jitter? Do you mean Rj, Dj, Tj? Are you
measuring Time Interval error, cycle-to-cycle, or something else?

I would recommend doing some reading. You can start at
http://www.agilent.com/find/jitter

Scroll down to "Key Library Information" and download (and read) all of
the White Papers and Application notes.

One of the first things you'll find is that it's probably impossible to
measure 1psec of jitter. As with any other measurement, there is the
concept of the smallest measureable unit. In the jitter world, this is
the Jitter Measurement Floor, and typical values are 80 fsec to 2 psec.

I personally can't imagine anything going on in an FPGA that would be
affected by 1 psec of jitter. More info would be advisable.

GS


Re: 1pSec Jitter
Quoted text here. Click to load it
... snip ...
Quoted text here. Click to load it
... snip ...
Quoted text here. Click to load it

Circa 1970 I built a system for transmitting voice band, which was
basically pulse duration modulated.  The start was controlled by a
separate clock.  IIRC signal/noise measurements on the results
indicated less that 1psec short term jitter.  My memory seems to
specify a pulse width in the range 0.25 to 1.25 uSec at about 12
Khz repetition rate, and a s/n ratio of better than 90 db.

We were only interested in the noise level in the telephone audio
band, roughly 300 hz to 3600 hz.  We traded off repetition rate to
simplify (and cheapen) equalization and aliasing filters, and met
all signal quality objectives.

--
"If you want to post a followup via groups.google.com, don't use
  the broken "Reply" link at the bottom of the article.  Click on
We've slightly trimmed the long signature. Click to see the full one.
Re: 1pSec Jitter
Sorry,

The Osc driving the FPGA calls for 1pSec jitter.

I am just trying to understand the 2 methods and how they relate to FPGA
requirements.

JG


Quoted text here. Click to load it



Re: 1pSec Jitter
Quoted text here. Click to load it

The oscillator calls for?  I thought this was a requirement from the
FPGA.  Do you mean that the FPGA calls for an oscillator jitter not to
exceed 1 ps?  What is the frequency?  Is the FPGA running a PLL based
on the oscillator?  Basically, what fundamentally is setting the
jitter requirement and why?

--
Thad

Re: 1pSec Jitter
Quoted text here. Click to load it



Do you mean the application specifies an oscillator with <1pSec jitter?

Quoted text here. Click to load it



Tight requirement. What is the specific application?

Quoted text here. Click to load it

There are more than two methods for measuring jitter (depending on just
what it is you are trying to measure). Frequency domain measurements
are commonly used for Dj prediction (although different test equip.
mfrs use different techniques). Time domain for cycle to cycle and
random jitter.
Long term drift (just what long term is depends on the system) may or
may not be an issue - that (just like all the other jitter sources) is
system dependent.

Note that different mfrs equipment will give you different results -
even a different set of probes will vary the measurement, particularly
at the speed you seem to need.

Quoted text here. Click to load it
What FPGA? What application?

Quoted text here. Click to load it

When testing high speed links I designed the physical layer for,
(5Gb/s) we used Tektronix equipment. Based on what I saw, they had some
of the best equipment. Look here
http://www2.tek.com/cmswpt/tifinder.lotr?cn=oscilloscopes&lc=EN
for some app notes.

In our application, we had to worry more about cycle to cycle and short
term peak / rms jitter, but without knowing more I can't say what your
app would consider an issue.

Cheers

PeteS


Re: 1pSec Jitter
On Sat, 14 Jan 2006 23:10:55 +1100, "Joe G \(Home\)"

Quoted text here. Click to load it

The only meaningful way to measure jitter is RMS. And even then, you
have to specify the time interval over which it's to be measured.
Peak-peak is poorly defined, but figure it's roughly 5 times RMS.

In the telecom biz, any time variances measured within 0.1 second or
less is "jitter", and above that it's "wander."

A normal sampling scope measures one or at most a few periods of the
input signal, which is "short-term" or "single period" jitter.

1 ps jitter is hard to measure. There are crystal oscillators that can
do less than 1 ps. By the time you pass it through an FPGA, expect the
result to be 10's of ps, maybe more.

Why do you need 1 ps jitter?

John




Re: 1pSec Jitter

Quoted text here. Click to load it

I'd put my money on the "idiot manager" option. Idiot systems engineers
also exist - "we've got this circuit which introduces 99psec of jitter,
and the error budget is 100psec, so the clock can't introduce more than
1psec of additional jitter".

Then there is idiot sales/marketing person who tells you that he/she
can sell hundreds of units if you can just break the second law of
thermodynamics.

--
Bill Sloman, Nijmegen


Re: 1pSec Jitter


Quoted text here. Click to load it

Probably the same guy that was upgrading to a 32-bit CPU and needed a
32-bit ADC to match.

John



Re: 1pSec Jitter
On Mon, 16 Jan 2006 13:06:15 -0800, the renowned John Larkin

Quoted text here. Click to load it

bits ~= dB/6


Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
We've slightly trimmed the long signature. Click to see the full one.
Re: 1pSec Jitter
On Mon, 16 Jan 2006 16:30:03 -0500, Spehro Pefhany

Quoted text here. Click to load it

So 32 bits is 192 dB. Isn't that just about the ratio of 1 atm to the
threshold of hearing?

John



Re: 1pSec Jitter
On Mon, 16 Jan 2006 13:55:42 -0800, the renowned John Larkin

Quoted text here. Click to load it

This web page says < 1E9, so >180dB.

http://hyperphysics.phy-astr.gsu.edu/hbase/sound/intens.html

by their info the threshold of pain is 0.003 of 1 atm.

I guess things would get nonlinear when you start to approach one bar
even if it didn't rupture your eardrums.


Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
We've slightly trimmed the long signature. Click to see the full one.
Re: 1pSec Jitter
Quoted text here. Click to load it

Have you ever seen that stock footage of a nuke? There's a very visible
shock wave of some kind, that's obviously traveling faster than Mach 1.

Cheers!
Rich


Re: 1pSec Jitter
Quoted text here. Click to load it

***Warning***Off-topic***Warning

If you are talking about the "stock footage of a nuke" that
I think you are talking about, I believe that spherical front
is a visualization of the Cherenkov Effect.

See:
  http://almaz.com/nobel/physics/cherenkov.html
  http://www.gae.ucm.es/~emma/tesina/node4.html

Roberto Waltman

[ Please reply to the group, ]
[ return address is invalid. ]

Re: 1pSec Jitter

Quoted text here. Click to load it

Supersonic shock waves.  What's next?!

--
  Keith

Re: 1pSec Jitter
Quoted text here. Click to load it

All shock waves are supersonic.  That's why it's a shock wave and not an
ordinary sound wave.  There's a big increase in entropy in its wake, too.

Cheers,

Phil Hobbs

Re: 1pSec Jitter

Quoted text here. Click to load it

Years ago, I saw a satellite video of Mt. St. Helens going off, and it
sent out what must have been a shock wave all the way to the next-door
states. In the vid, it happened in seconds, but I have no idea what
the time-scale was compared to real-time. But it looked like the sort
of condensation wave that you see with shock waves. I've done a little
searching, but haven't really found out anything about it, and I guess
MSH is pretty much old news these days.

Thanks,
Rich



Re: 1pSec Jitter
Quoted text here. Click to load it
[snip]
Quoted text here. Click to load it
Is a supersonic shockwave the explanation of the effect one sometimes
notices with a nearby lightning strike: see the flash, & hear almost
simultaneously a sharp crack, like a stick snapping. A second or so
later, comes the boom. So that crack must have been supersonic?

Re: 1pSec Jitter
Quoted text here. Click to load it

Did the "sharp crack" come out of your radio?



--
--
snipped-for-privacy@rahul.net   forging knowledge


Re: 1pSec Jitter
Quoted text here. Click to load it

Much simpler explanation.  The speed of sound varies with frequency.

--
"If you want to post a followup via groups.google.com, don't use
  the broken "Reply" link at the bottom of the article.  Click on
We've slightly trimmed the long signature. Click to see the full one.

Site Timeline