Measuring Jitter Below 10ps

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bhobba

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Measuring Jitter Below 10ps
« on: 15 Mar 2013, 02:12 am »
Hi Steve

I seem to recall you mentioning in a post over on SNA that accurately measuring Jitter below 10ps was an issue and you need special equipment to do it, with not a lot of it being about.  I seem to also recall you mentioning for your converters you actually didn't measure the jitter directly but rather 'deduced' it from the jitter measurements of the clock.

Is this true or have I got it wrong.  I have mentioned it a few times but last time here is the response I got:
'REALLY!!!!!!!!!!!!!!!!!!!!????????????? It is only hard if you have the wrong equipment. I'll leave it at that.'

Thanks
Bill

audioengr

Re: Measuring Jitter Below 10ps
« Reply #1 on: 15 Mar 2013, 05:57 pm »
Hi Steve

I seem to recall you mentioning in a post over on SNA that accurately measuring Jitter below 10ps was an issue and you need special equipment to do it, with not a lot of it being about.  I seem to also recall you mentioning for your converters you actually didn't measure the jitter directly but rather 'deduced' it from the jitter measurements of the clock.

I have measured worst-case direct P-P jitter over all frequencies and its in the specs for the OR5.  I don't deduce from the clock or quote the clock  like many other manufacturers do.

I have only recently begun using the histogram, which I am finding very useful.  Even if the max deviation in the cycle-time, (which is the worst-case jitter event) is 400psec, these events can be fairly rare.  The bulk of the jitter can still be in a peak about 50 psec wide.  This is what I'm seeing now with this mod.  Now I am convinced that not only is the spectra interesting, but the shape of the distribution of the jitter is maybe even more important.

Steve N.

Tyson

Re: Measuring Jitter Below 10ps
« Reply #2 on: 15 Mar 2013, 06:05 pm »
I guess that's similar to distortion in amps - THD tells you nothing about how it sounds, but knowing if the distortion is high order or low order, even or odd tells you a lot.