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CDCE706: about runt clk reference influence to CDCE706

Vera Mao
Expert 5065 points

Part Number: CDCE706

Hi dear supporting team,

In customer's system, there may be some possibility to have runt clk as  ref to CDCE706, pls help evaluate what's the influence to 706,customer will need decide whether to use it or not. 

1. will it loss lock?

2. if yes,  will it still have output?

3. if it still have output, how about the phase noise will be?  do we have some test data? 

runt clk waveform could be : loss several cycle,  changed duty cycle, changed amplitude,  and etc... as below, the green curve is the runt clk, the jitter is around 2ns:

  • 0
    TI__Expert 4415 points

    Hi Vera,

    Whether the device loses lock or not will depend on how far out of specification the runt waveform is. We can't guarantee that the device will retain lock if the input is outside of the datasheet specifications.

    Since the CDCE706 does not support output mute/does not have a lock detect, there will still be an output clock as the VCO is still running. However, since it is not locked the VCO will free run and the output frequency will not be defined. As a result the phase noise also will not be defined.

    Regards,

    -Tim

  • 0 in reply to Tim Chao Li
    TI__Expert 5065 points
    Hi Tim,
    thank you for your reply!
    as for d/s specification, do you mean the frequency, Tr/Tf, duty cycle spec? any other specs? do we have lock window spec like LMK048**?
  • 0 in reply to Vera Mao
    TI__Expert 4415 points

    Hi Vera,

    Correct, I am referring to the 'CLK_IN Requirements' section of the datasheet on page 6. We don't have a lock window spec, but the expected PLL lock time is described on page 35 of the datasheet under 'PLL Lock Time'.

    Regards,

    -Tim