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Jonathan Harris

ADC Noise: How the Clock Input Can Help

Jonathan Harris
jonharris0
jonharris0
1/27/2014 8:30:26 AM
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Blogger
Re: Phase noise and Jitter
Hi amrutah, these are all great points and questions.  Indeed the clock is often overlooked when it shouldn't be.  Definitely one of the biggest contributors to noise in an ADC is the phase noise of the input clock source.  Other factors may not be as big but should not be overlooked.  The noise impact will be less from what is picked up via a poor layout than from a clock source with poor phase noise or poor spurious even.  I think you'll enjoy my next post.  I'll be looking at close in vs wideband phase noise and how they affect the ADC in different ways.  Thanks for the great comments and questions!

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amrutah
amrutah
1/25/2014 1:57:48 PM
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Master
Phase noise and Jitter
Jonathan,

   I will be eagerly waiting for your next blog post.  How the low and high frequency components phase noise affect the ADC noise.  Different jitter that affect the ADC noise, meaning contributions of peak litter, period jitter or total accumulated jitter.

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amrutah
amrutah
1/25/2014 1:49:27 PM
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Master
CLOCK phase noise/Jitter
Jonathan,

   I think the contribution of phase noise/jitter of the clock source is the main contributor to ADC Noise compared to the noise that the clock picks on the way to ADC. How substantial can the noise contribution be compared to the jitter?

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amrutah
amrutah
1/25/2014 1:08:27 PM
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Master
Clock input

Yes, I agree that the clock input source can be one source of noise and usually is considered at last moment. As you mentioned modelling it as a mixer should give a good analysis upfront when dealing with the noise analysis and specification limit.

   Usually the high speed clock source will be a PLL/DLL system which cannot be placed close to the ADC, and as such having a filter makes it more viable solution.  But that increases the BOM or onchip area

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More Blogs from Jonathan Harris
We look at using a DC/DC converter along with an LDO to drive the ADC power supply inputs.
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There are some disadvantages when driving low input supply voltages, where multiple LDOs may be required.
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