Can anyone explain how to measure jitter?

ezkcdude · 27th February 2006, 05:18 PM

I would like to be able to measure jitter on the coaxial output of my SqueezeBox. Does anyone here know the simplest, or preferably cheapest, way to perform this measurement?

I_Forgot · 27th February 2006, 09:35 PM

There are specialized test instruments for the purpose. I used to use an HP 12 Gbps jitter test set at TI to measure the jitter out of SERDES and hypertransport chips for internet infrastructure switches. Those boxes cost $300k each. I also played with some Wavecrest boxes that were sooooo sexy! They did a lot of statistical analysis and calculated jitter limits based on a sample measurement- i.e if your needed jitter induced error down to 1 per 10^20 bits, you didn't have to send 10^20 bits through the thing to see if there were any errors. Even at 10 Gbps it takes loooong time to send 10^20 bits, so being able to confirm error rate numbers with just a sample was a big timer saver. The trouble was, many clients didn't believe the statistics, so we often had to run the long tests anyway.

Unfirtunately I no longer have access to that sort of instrument...

I_F

ezkcdude · 27th February 2006, 09:57 PM

$300K? That's not exactly what I had in mind.

jcx · 28th February 2006, 02:19 PM

you usually need better measurement equipment than what you are trying to measure

you can try to measure the results of jitter on the analog output

I've seen noise "skirts" on test tones from a portable CD analog output measured with a Lynx sound card that were presumably caused by the portable's clock jitter

looking at level/freq/load dependency could help separate DAC Vref/psrr from clock jitter induced noise in this sort of indirect measurement

direct measurements of clock jitter are going to require more expensive equipment

other options are good ref clocks, now noise multipliers and plls to translate the jitter spectrum to a frequency where cheaper equipment has sufficient resolution

look at crystal manufacturer’s web site’s tech articles on jitter/phase noise

Circuit wanted for a Low Phase noise 100MHz Clock:

http://www.diyaudio.com/forums/showt...931#post295931

27th February 2006, 05:18 PM	#1
ezkcdude diyAudio Member Join Date: Dec 2005 Location: Atlanta	Can anyone explain how to measure jitter? I would like to be able to measure jitter on the coaxial output of my SqueezeBox. Does anyone here know the simplest, or preferably cheapest, way to perform this measurement?

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27th February 2006, 09:35 PM	#2
I_Forgot diyAudio Member Join Date: Jan 2005 Location: Phoenix, Az.	There are specialized test instruments for the purpose. I used to use an HP 12 Gbps jitter test set at TI to measure the jitter out of SERDES and hypertransport chips for internet infrastructure switches. Those boxes cost $300k each. I also played with some Wavecrest boxes that were sooooo sexy! They did a lot of statistical analysis and calculated jitter limits based on a sample measurement- i.e if your needed jitter induced error down to 1 per 10^20 bits, you didn't have to send 10^20 bits through the thing to see if there were any errors. Even at 10 Gbps it takes loooong time to send 10^20 bits, so being able to confirm error rate numbers with just a sample was a big timer saver. The trouble was, many clients didn't believe the statistics, so we often had to run the long tests anyway. Unfirtunately I no longer have access to that sort of instrument... I_F

27th February 2006, 09:57 PM	#3
ezkcdude diyAudio Member Join Date: Dec 2005 Location: Atlanta	$300K? That's not exactly what I had in mind.

28th February 2006, 02:19 PM	#4
jcx diyAudio Member Join Date: Feb 2003 Location: ..	you usually need better measurement equipment than what you are trying to measure you can try to measure the results of jitter on the analog output I've seen noise "skirts" on test tones from a portable CD analog output measured with a Lynx sound card that were presumably caused by the portable's clock jitter looking at level/freq/load dependency could help separate DAC Vref/psrr from clock jitter induced noise in this sort of indirect measurement direct measurements of clock jitter are going to require more expensive equipment other options are good ref clocks, now noise multipliers and plls to translate the jitter spectrum to a frequency where cheaper equipment has sufficient resolution look at crystal manufacturer’s web site’s tech articles on jitter/phase noise Circuit wanted for a Low Phase noise 100MHz Clock: http://www.diyaudio.com/forums/showt...931#post295931

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