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Jonathan Harris

ADC Noise: The Clock Input & Phase Noise (Jitter), Part 1

Jonathan Harris
jonharris0
jonharris0
2/27/2014 1:57:11 PM
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Re: po-tah-to.. to-mah-to...
The /10 error has now been corrected.  I also corrected a sign in the area equation.  Once again I apologize for the oversight on these errors.

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jonharris0
jonharris0
2/20/2014 3:29:09 PM
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Re: po-tah-to.. to-mah-to...
Thanks for the great comments and questions amrutah!  To address your first question, yes the 2 is to account for each side of the fundamental tone.  The 1/10 factor is an error on my part.  When copying over equations in the equation editor I mistakenly left a /10 in the equation when it shouldn't be there.  I'll correct that in my next blog.  Thank you for spotting this and I ask you and my readers to forgive my mistake.  To address your second question...you'll see a bit more on that as we keep going, but the close-in jitter has more effect on the EVM than on the wideband noise since the Nyquist zone is >> the noise close in to the fundamental. And to your last comment, I like that idea.  I'll have to think about trying to formulate a blog around that sort of topic! :-)

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amrutah
amrutah
2/19/2014 1:26:30 AM
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po-tah-to.. to-mah-to...
Jonathan,

  The analogies potato and tomato is good and interesting.

  Another thing oftenly used are the FFT and EYE diagram to analyse the phase noise and Jitter respectively.

  It would be helpful if you can touch upon FFT and eye diagram co-relation. Along with the frequency domain to time domain analysis, it will also be helpful to correlate using time domain to time domain.

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amrutah
amrutah
2/19/2014 1:19:14 AM
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wide band phase noise
"The wide band phase noise has the most impact.."

  So as we move towards the origin (or away from the sampling freq) the phase noise is more, meaning the rms jitter is more.  How can we quantify about the peak jitter or period jitter of the clock source.

  Can we say that the 1/f2 portion of the phase noise will help us formulate peak jitter?

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amrutah
amrutah
2/19/2014 1:04:09 AM
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Master
tjrms equation
Jonathan:

  Thanks  for the blog and super simple explaination.

The factor of "2" in the numerator is to quantify that the noise is on both side y-axis.   The 2nd equation for tjrms, what is the factor 1/10 in the numerator for?  

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More Blogs from Jonathan Harris
Previously in this blog series we looked at using a DC/DC converter (switching regulator) in combination with an LDO to drive the power supply inputs to an ADC. What we found was that using the DC/DC converter to step down the input voltage for the LDO was a much more efficient way to drive the power supply inputs to an ADC.
We look at using a DC/DC converter along with an LDO to drive the ADC power supply inputs.
I thought it would be good to continue looking at the example I gave in my last blog where we looked using fewer LDOs and combining power supply rails on an ADC while maintaining isolation with ferrite beads.
There are some disadvantages when driving low input supply voltages, where multiple LDOs may be required.
Keeping the power supply inputs on separate domains can minimize crosstalk and make it much harder for noise to interfere with ADC performance.
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