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Frequncy generator

Discussion in 'Electronic Design' started by GPG, May 3, 2007.

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  1. GPG

    GPG Guest

  2. GPG

    GPG Guest

  3. Andrew Holme

    Andrew Holme Guest

    I would say not.

    The 40Hz comparison frequency is too low. That's going to force you to use
    a very low loop bandwidth, which will make it slow to lock.

    You'd probably need to convert the mixer inputs to sine waves first; and
    it'll produce sum and difference products, so you'd need a good low pass
    filter to remove the 10.4-13 MHz sum product whilst passing the .4-4 MHz
    difference. Finally, you'd need to square-up the sine waves again before
    feeding them to the dividers.

    If the aim is to produce low frequencies with high resolution, how about a
    DDS?

    If you want a PLL with small steps, consider Fractional-N.
     
  4. GPG

    GPG Guest

    That is a concern. Once locked the loop filter can be slow, and I had
    thought to use a lock detect circuit to change the current of the
    detector for speeding up lock time.
    Had a D FF in mind for that part, only the difference out.
    Had a brief look, still reading.
    Will research. Thanks.
     
  5. John Larkin

    John Larkin Guest


    Only if you can tolerate immense amounts of phase noise.

    This sort of thing looks ideal for a cheap DDS chip. I'd maybe double
    the clock first, to 20 MHz, to not run too close to Nyquist.

    John
     
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