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Divide/multiply clock signal

  1. Nov 20, 2016 #1
    hi,

    i need a 28.8MHz clock signal (digital/square wave).
    Unfortunately this specific frequency is hard to get so i need to make one myself.
    I guess the keyword here is "frequency synthesizer"?
    Or how would you approach this?
    (to get the 28.8MHz clock signal out of other more commonly available frequency oszillators)
    If you could share certain ICs you would recommend for this issue that would be great! :)

    thank you!
     
  2. jcsd
  3. Nov 20, 2016 #2

    Baluncore

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    The answer will depend on how much phase noise you can tolerate.
    Do you need exactly 28.8MHz or will something close be OK?
    What is your application?
    What frequency clocks are available now to use for synthesis or locking of the 28.8MHz.
     
    Last edited: Nov 20, 2016
  4. Nov 20, 2016 #3

    phinds

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    Yes it is. Have you googled that?

    I did and immediately got a hit on the TI SN74LS624N which you could use to give you half that frequency and then follow it with a one-shot to double it. No statement on the accuracy though.

    EDIT: single one-shot follower wont' work. You'll need two of them then an OR gate.
     
  5. Nov 21, 2016 #4
    First, thanks a lot for your answers!

    It should be pretty close to 28.8MHz (TCXO/temperature compensated would be good in order to keep the frequency drift lower).
    (28.75 to 28.85MHZ is ok for sure)
    A low quality crystal on a SDR (software defined radio) stick shall be replaced.

    So i could take a 14.4MHz TCXO and double the frequency?
    Do you know an IC that can just double my frequency?

    I already did some research but im quite unsure yet (there are way too many kind of ICs [dividers,clock synthesizers,multiplier, buffers etc]) so it would really help a lot if you could show me the right path by some example ICs maybe? :)

    @phinds: I checked the TI SN74LS624N, so i can halve my frequency with your IC, so is there also one i can multiply my frequency by 2?
    Im also quite unsure how i would use the TI SN74LS624N right yet, on what ports should i provide the clock signal and on what port i then could expect the halved output signal? Does it halve the signal by default or do i have to apply certain settings on a certain port?

    Sorry for all the questions, i hope i can clear some out with your help :)
     
  6. Nov 21, 2016 #5

    phinds

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    I don't know the details, I just Googled the relevant phrase and got that chip. Put two one-shots on the output, one with an inverter in front, and then OR the outputs of the one-shots.
     
  7. Nov 21, 2016 #6

    analogdesign

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    Last edited by a moderator: May 8, 2017
  8. Nov 21, 2016 #7

    berkeman

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  9. Nov 22, 2016 #8

    vk6kro

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    The United States website of EBay lists about 10 suppliers of 28.8 MHz crystal oscillators.

    Many of these are high quality units ( eg 0.5 parts per million accuracy) with prices to match. You get what you pay for. :-)

    There is one supplier who has ceramic resonators at a much lower price, but these are fairly unstable.

    Most crystal manufacturers would probably quote you a price for making you one to order.
     
  10. Nov 22, 2016 #9
    ok thank you all for all your replies!
    I didnt know there also were programmable oscillators available, so thanks for that hint!

    So i guess i just could grab one of these, e.g.: http://www.mouser.de/ProductDetail/Microchip-Technology-Micrel/DSC8001BI2/?qs=sGAEpiMZZMuOKVxQlXmfz2joUnuME8vyBrzHzq0PCJAZq5JymFKMOA%3d%3d [Broken]

    I suppose after i bought the parts i will be asked to provide a value for the oscillators frequency (so i could tell them 28.8MHz).
    Seems like a pretty easy solution?
    So i wouldnt need to build circuits that divide/multiply my clock signals...
     
    Last edited by a moderator: May 8, 2017
  11. Nov 22, 2016 #10

    berkeman

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    Yes, they are very handy. You just specify the frequency when you make your purchase from Mouser or Digikey. :smile:
     
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