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TLK1221 PRBS & BERT

YI WANG
Prodigy 30 points
Other Parts Discussed in Thread: TLK1221

We did some test using TLK1221 built-in PRBS and BERT to test BER and compared it with a BERT instrument (MP1800A). The BER result using TLK1221 result seems always better than BERT instrument.

 

Can anyone tell me what is possible reason? Is TLK1221 BERT accurate or not?

 

Thanks,

  • 0
    TI__Mastermind 20820 points

    Hi Yi,

    I am not familiar with the MP1800A so I cannot comment on its performance.

    The TLK1221s built in PRBS generator and verifier are desigtned to supply a reliable source and sink for PRBS data. This can be implimented in loopback mode for on board pcb testing or it can be used to inface with a BERT (Tx or Rx) as well as any other device that support PRBS.

    Are you having a problem with the device that I can help you address?

    Regards,

    Mike     

  • 0 in reply to Michael Peffers
    Prodigy 30 points

    Hi Mike,

     

    We used an scope to monitor SYNC signal. The scope has a maxim sample rate of 5G/s. The data rate of PRBS7 is ~1.23Gbps with a reference clk of ~123MHz.  We captured SYNC signal when errors were detected. The pulse width we obtained was never smaller than 100ns. Here I am wondering if TLK1221 detects error per sequence of PRBS7, not per BIT. One PRBS7 sequence is 127bit, ~100ns for 1.25Gbps data rate. So if there is 2 or more erros in one sequence of PRBS7, the SYNC will only be triggled low once, right?

     

    Thanks,

  • 0 in reply to YI WANG
    TI__Mastermind 20820 points

    Hi Yi,

    Sorry for my delay in response I was traveling last week and had several lingering projects to finish up. I need to check with a designer on this because I am not sure. I will respond when I can confirm an answer for you.

    Regards,

    Mike

  • 0 in reply to Michael Peffers
    Prodigy 30 points

    Hi Mike,

     

    Any words from the designer?

     

    Thanks,

  • 0 in reply to YI WANG
    TI__Mastermind 20820 points

    Hi Yi,

    When an error is detected by the TLK1221 a minimum if two clock cycles has to pass before the error is cleared. The PRBS pattern checker computes the expected value based on previous values, so an error in the previous sample would cause the current expected value to be wrong as well, meaning that a correct pattern would still be marked as a “fail.”

    The TLK1221 has cannot report a reliable BER because if there are multiple errors in a data stream the synch pin simply moves to low and stays there until a valid pattern is seen by the part.

    Mike