• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 1 answer
  • Subscribers 21 subscribers
  • Views 137 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMK01801: Clock Distributer

Terry Liu70
Intellectual 500 points
Part Number: LMK01801


Hi,

In my application, input = 1GHz sine wave signal with -150dBc/Hz phase noise @100k offset. I like to introduce a frequency divider then output a 100MHz signal with better than -165dBc/Hz phase noise @ 100k ofs. I looked into LMK01801, but the noise floor doesn't seem to be good engouth. 

Please advise a proper moldel number that meets above requirements.

Thanks,

Terry

  • 0
    TI__Genius 12490 points

    Hi Terry,

    I am confused. If your signal source has a noise floor of around -150dBc/Hz @ 100k offset, then any device you instantiate following that device will be subject to the noise floor of the signal. A noise floor of -165dBc/Hz @ 100k offset is only going to be possible if you have a source with a noise floor lower than that, and then - depending on the frequency - your noise floor can be satisfied by the whole signal chain.

    Thanks,

    Michael

  • 0 in reply to Michael Srinivasan
    Intellectual 500 points

    Hi Michael

    Input 1GHz signal with phase noise of -150dBc/Hz, when frequency divided by 10, output a 100MHz signal, the ideal phase noise should be -150 - 20 * log (10) = -150 - 20 = 170dBc/Hz. Thus, I think -165dBc/Hz target makes sense. 

    Again, please advise if TI has any part that meets this spec, Thanks,

    Terry

  • 0 in reply to Terry Liu70
    TI__Genius 12490 points

    Hi Terry,

    You would actually add that 20 * log (10), meaning you would be seeking a target of -135db/Hz. 

    This part would certainly meet that spec.

    thanks,

    Michael

  • 0 in reply to Michael Srinivasan
    Intellectual 500 points

    Hi Michael

    You mean,

    Device input = 1GHz, -150dBc/Hz @ 100k

    (LMK01801) Divide by  10

    Device Output = 100MHz, phase noise will add 20dB to -130dBc/Hz?? Thus -135dBc/Hz floor is good to use...

    This is beyond my knowledge, I never saw phase noise getting worse when dividing frequency.

    Terry

  • 0 in reply to Terry Liu70
    TI__Genius 12490 points

    Hi Terry,

    I just realized I made a mistake - I was confusing multiplication for division. 

    The noise floor for this device will be roughly -162dBc/Hz at 100MHz. We do not have a device with a built in divider that also has a noise floor of -165dBc/Hz at that high of a frequency. Will that work?

    Thanks,

    Michael

  • +1 in reply to Michael Srinivasan
    Intellectual 500 points

    Hi Michael

    Thanks for your kind assistance. I just found an ADI part that offers -170dB noise floor.

    Terry