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Question on Sampled (JItter) PNoise analysis

YutaoLiu

Hi everyone,

I am doing noise analysis on a track and hold circuit (a switch cap followed by a 16GHz 3dB-BW opamp model) with PSS+ Pnoise. The tool version I am using is ICADVM20.1-64b.

The switch is driven by a 8GHz 25% duty cycle clock, and the sw is closed when clock level is LOW.

I used sampled (jitter) mode, configured "sampled phase" for the "timing event" , and set "sample per period" as 8.(setup is as shown in pic below).

"Total noise" result varies in different timing event, and the noise contribution from the switch also change.

Why the total noise is different at different sampling instant? In my understanding, the sampling behavior only folds noise back to 0~Nyquist frequency (4GHz in my case).  I have though the total noise should be independent on the sampling instant.

What is the possible fact to generate this difference? Is there any document talking about this?

Thanks and regards,

Yutao

  

  • Dear YutaoLiu,

    YutaoLiu said:
    Why the total noise is different at different sampling instant? In my understanding, the sampling behavior only folds noise back to 0~Nyquist frequency (4GHz in my case).  I have though the total noise should be independent on the sampling instant.

    I think you might consider reviewing the difference between a sampled jitter analysis and a timeaverage analysis. In a sampled jitter analysis the noise is only evaluated at the sample point you specify and is not averaged. Hence, it does depend on the sample instant. Please consider reading the helpful on-line support article at URL:

    https://support.cadence.com/apex/ArticleAttachmentPortal?id=a1O0V000009EStcUAG&pageName=ArticleContent

    I hope this helps clarify the difference in the two types of noise analyses....and I've managed to understand your question correctly!

    Shawn

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