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ADC 85MHz Clock Recommendation

Des Coghlan
Prodigy 100 points
Other Parts Discussed in Thread: LMK03318, LMK03318EVM, TICSPRO-SW

I need an ADC clock at multiple of 85M; 340, 425 and 510MHz, jitter < 120femto-secs over 1k to 10MHz.. Whichever of the 3 freq selected, I want a fixed 85M - Div by 4,5 or 6. I have a 80M VCXO. Is there a PLL IC that can accept 80M Ref, generate 340, 425 and 510M , with a fixed 85M out? - eg programmable divider =4, 5 or 6? 

  • 0
    TI__Mastermind 32575 points

    I suggest the LMK03318 low-jitter clock generator.  The fractional-N PLL can tune its internal VCO to 5100 MHz and lock the 80 MHz VCXO reference.  The VCO post-divider (3-bit: /2-/8) and integer output dividers (8-bit: /1-/256) could be programmed to generate the fixed 85 MHz output and any of the three frequencies you need.

    Here are some resources to assist in your device evaluation if you are interested.

    LMK03318EVM - Link to EVM board

    TICSPRO-SW - Link to EVM programming software (In TICS Pro, navigate to: Select Device > Clock Generator/Jitter Cleaner (Single Loop) > LMK03318)

    LMK03318 configuration files for each of the 3 output frequency cases (340M, 425M, and 510M), which you can load in the TICS Pro GUI software to program the device EVM.

    LMK03318_priref=80M_out1=85M_out3=340M.tcs

    LMK03318_priref=80M_out1=85M_out3=425M.tcs

    LMK03318_priref=80M_out1=85M_out3=510M.tcs

    Regards,
    Alan

  • 0 in reply to Alan O
    Prodigy 100 points
    Thanks. Looks good. Can you confirm the jitter on the 340/425/510M outputs ?
    I desire < 120 femto-secs; para 10.1 on p27 of data sheet quotes 200fs in Integer and <350fsecs in fractional PLL mode. With 80M in and VCO @ 5.1G, I will be in fractional PLL mode.
  • 0 in reply to Des Coghlan
    TI__Mastermind 32575 points
    I simulated 125 fs RMS jitter (typical) for the 340/425/510M outputs. The jitter spec of <210 fs in fractional mode (assumes 50 MHz reference) would be more applicable to your case, since you're using a higher reference frquency of 80 MHz.

    Alan