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DS90UB936-Q1: Deserializer REFCLK Jitter Measurement

Sathishkumar
Prodigy 30 points
Part Number: DS90UB936-Q1

I have some below query regarding REFCLK specification in deserializer datasheet.

1) In the REFCLK specification,they have mentioned generally like "jitter". could you please tell me what type of jitter is that and how to measure/Validate?

2) There is frequency range (200kHz -10MHz) in test conditions column. I dont know what frequency range its denoting. 

 

Note: In my application REFCLK given from SOC.

  • 0
    TI__Guru** 103215 points

    Hello Sathish,

    The REFCLK frequency input to the device should be 23-26MHz frequency. It must meet a jitter requirement of < 200ps p-p

    p-p jitter can be captured with a scope and can be derived from RMS jitter.

    Best Regards,

    Casey  

  • 0 in reply to Casey McCrea
    Prodigy 30 points

    Hello Casey,

    Thanks,But i need some more clarification.

    1) Jitter requirement specifed in the datasheet for which type of jitter (Ex: Random phase jitter or periodic jitter or cycle to cycle jitter or some other else)?. Based on this only i can measure with scope.

    2) The REFCLK frequency is 23- 26 MHz. Then why they have mentinoed the freq range 200kHz -10MHz in test condition column for jitter specification. what its denoting?

    Regards,

    Sathishkumar

  • 0 in reply to Sathishkumar
    TI__Guru** 103215 points

    Hello Sathish,

    If you capture an RMS jitter measurement you can calculate a peak to peak jitter based on the desired BER. Typically for these systems we would use 10^-12. You can find the formulas for this calculation and the associated RMS multiplier for each BER commonly online. The jitter being measured in this case is a combination of DJ and RJ which includes cycle to cycle jitter.

    For the jitter measurement we are mainly concerned with jitter in a bandwidth range of 200kHz-10MHz. 

    Best Regards,

    Casey 

  • 0 in reply to Casey McCrea
    Prodigy 30 points

    Hello Casey,

    For the jitter measurement why we are cosidering only 200kHz - 10MHz bandwidth range. Could you please explain it briefly?

    Do i need to measure the jitter with oscilloscope only for the particular bandwidth?.If yes how can i measure the jitter for that particular bandwidth?

    Regards,

    Sathishkumar

  • 0 in reply to Sathishkumar
    TI__Guru** 103215 points

    Hello Sathish,

    The REFCLK is recovered using a PLL in the device, so the PLL bandwidth dictates the jitter which is tracked by the PLL. Outside of that range, the jitter should have little impact. 

    For measurement I would recommend using a proper high speed scope with a jitter analysis tool like DPOJET which lets you apply such filters. Alternatively if you want to capture the jitter using infinite persistence without concern for the frequency range and the jitter passes then this means in any other restricted band the measurement will pass as well. 

    Best Regards,

    Casey