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Issues with using abEyeCross.il (giving WRONG results when compared to EYE-Diagram)

RFStuff

Dear All,

 I am using abEyeCross.il from solution 11395772(https://support.cadence.com/apex/ArticleAttachmentPortal?id=a1Od0000000nX0ZEAU&pageName=ArticleContent).

This is to find peak-to-peak Deterministic jitter (DJ) when I give a supply sinusoidal noise ( of 20 mV amplitude and 11.11 MHz frequency).

I am giving a PRBS pattern of UI=31.25 pS as the input data stream. I am now finding the DJ in the output data stream.

I am trying to verify that whether  abEyeCross.il is giving correct result when I compare manually the Deterministic jitter from the actual Eye-Diagram.

But, Looks like I am getting wrong result from abEyeCross.il.

Can anybody please tell why it is giving wrong results. I am also posting the both way results below.

 abEyeCross.il Results:-

I use the commands in CIW as below:-

jit=abEyeCross(vtime('tran "/rxleq_lpbk") 0n 105n 31.25p 0 "rising")
srrWave:0x33bed0a0
DJ=peakToPeak(jit)


DJ=3.123789e-11 =31 pS



I got DJ = 31 pS

Below shows the DJ value I got from Eye-Diagram:-

Parents

  • If you plot an eye diagram with a period of 31.25p from 0n to 105n, what does it look like? 

    I wrote abEyeCross, and it works pretty reliably - but seeing the actual data would help. Can you log a case with support.cadence.com and then let me know the number, and then I'll take a look? I'd ideally need the PSF results from the simulation you're using.

    Regards,

    Andrew

  • in reply to Andrew Beckett

    Dear Andrew,

    Thanks a lot for your reply.

    Actually as I mentioned, my UI = 31.25 pS. So, when I give the UI value, spectre eye Measurement option automatically takes eye period as 2*UI. Hence you are seeing a eye period of 62.5 pS.

    Do you think that, if I  feed this :- jit=abEyeCross(vtime('tran "/rxleq_lpbk") 0n 105n 62.5p 0 "rising"), it will give correct result ?  Does the period in abEyeCross() mean 2*UI ?

    Kind Regards,

  • in reply to RFStuff

    abEyeCross needs the UI, because it looks at all the rising edges in the period you specify. So I'd expect a large peak to peak if you use 62.5p as the period, but a much smaller one if you're using a 31.25p period. You can (with the Eye Diagram assistant) manually set the period to be 31.25p and plot that. It's possible if the duty cycle is not 50-50 that the spread would be larger, but something doesn't look right since your peak to peak is similar to the period, which is a bit strange.

    That's why I'd like to look a the data.

    Regards,

    Andrew.

  • in reply to Andrew Beckett

    Thanks a lot Andrew. I will soon file a SR with appropriate data as mentioned by you and tell you the SR number.

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