" why is the serdes jitter specified for a particular freq
range like 12KHz to 20MHz"
The upper frequency limit is based on the bandwidth of the TX PLL. All
jitter frequency components above that will be attenuated by the TX PLL.
The lower frequency limit is based on the bandwidth of the RX CDR (clock
data recovery unit). All jitter frequency components below that will be
tracked (therefore attenuated) by the RX CDR.
The jitter frequency components between the two limits will close the
signal eye.
Thanks,
Vinu
On 02/18/2016 03:31 PM, Hithesh wrote:
If using scope for jitter measurement, make sure you calculate the scope
jitter noise floor. For a 13GHz scope we use, the jitter noise floor is
6pS. The typical spec is less than 3pS.
Related question - why is the serdes jitter specified for a particular freq
range like 12KHz to 20MHz.
What happens in this freq range.
Is this is the PLL loop frequency?
On Thu, Feb 18, 2016 at 1:03 PM, Ransom Stephens <ransom@xxxxxxxxxxxxxxxx>
wrote:
If the spec an has an SSB (single sideband) app, you can integrate the
sideband spectrum to get, as mentioned by Jose, the band-limited rms RJ.
Jose also pointed out that the result probably won't be more than 20-30%
comparable to other techniques. You'll probably come in low. Fine. Now use
your low bandwidth scope on a data pattern that's clock like, but at a low
enough rate that your scope can swallow it, you know, 111000111000...or
whatever fits.
If the histograms look Gaussian, take the rms of the histogram and compare
it to what you got with the spectrum analyzer. Average them, and figure
you're still under-estimating, but might be within 25% of the "truth."
It's probably cheaper to rent a high bandwidth scope from Tek, Lec, or Key
and use their fancy jitter analysis code to get all your jitter numbers
than
to rent a phase noise analyzer--and still be band limited. If you have real
worries that your RJ might be way too high, study the reference clock.
Truly
random jitter comes from thermal sources and shouldn't be very high. If it
is, you have other problems in that clock.
Ransom
_____________________________
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Signal Integrity Sage
Ransom's Notes: Training, content, and consulting/analysis since 2005
www.ransomsnotes.com
Measure of Things - Science & Technology blog at Electronics Design News:
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-----Original Message-----like
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Tesla
Sent: Thursday, February 18, 2016 1:19 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Measure RMS jitter of Serdes using spectrum analyzer
Hi Experts
I am curious about a idea using spectrum analyzer to measure the RMS
jitter of serdes. Because we do not have a high enough bandwidth scope.
For low frequency clock, we can use spectrum method to measure the RMS
jitter of clock source. Suppose we let the Serdes is outputing 101010....
clock pattern. Can the RMS jitter be measured using spectrum analyzer
low frequency clock?
Thanks a lot for your advice.
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