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RMS jitter from eye diagram

34892

Hi,

 

I am trying to find RMS jitter of the clock coming out of my ADC ( in post layout sim). I can plot eye diagram, but am not sure how to get the RMS value of jitter. Is there a way (may be using calculator or otherwise) to get the RMS value? I think the eye diagram gives the peak-peak value of jitter.

(posting again, as the pervious post was in wrong category) 

Thanks

Parents

  • Hi 3489,

    I believe what you need to do is to compute the time interval error (TIE) as a function of zero-crossing and then determine its rms value. Please note, however, that "jitter" is defined over a specific bandwidth. Hence, the rms value you compute is limited by the sample size of the TIE you compute. For example, the minimum frequency of the time interval error is determined by the time span of the simulation you analyze and the maximum frequency is essentially 1/(2*your clock period). If you are trying to compute the rms jitter over a specific frequency band, you will need to set the simulation time and your analysis period accordingly. There is an calculator function called "abs_jitter" that will compute the time interval error on a periodic waveform. An example of its syntax for a clock waveform named hsclki_clipped with period 1/fin and switching threshold level vth is as follows:

    hsclki_tie = abs_jitter( hsclki_clipped "rising" vth ?yUnit "s" ?Tnom 1.0/fin )

     

    I hope this helps!

     

    Shawn 

Reply

  • Hi 3489,

    I believe what you need to do is to compute the time interval error (TIE) as a function of zero-crossing and then determine its rms value. Please note, however, that "jitter" is defined over a specific bandwidth. Hence, the rms value you compute is limited by the sample size of the TIE you compute. For example, the minimum frequency of the time interval error is determined by the time span of the simulation you analyze and the maximum frequency is essentially 1/(2*your clock period). If you are trying to compute the rms jitter over a specific frequency band, you will need to set the simulation time and your analysis period accordingly. There is an calculator function called "abs_jitter" that will compute the time interval error on a periodic waveform. An example of its syntax for a clock waveform named hsclki_clipped with period 1/fin and switching threshold level vth is as follows:

    hsclki_tie = abs_jitter( hsclki_clipped "rising" vth ?yUnit "s" ?Tnom 1.0/fin )

     

    I hope this helps!

     

    Shawn 

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