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PLL locking problem

Discussion in 'CAD' started by cici, Dec 1, 2003.

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  1. cici

    cici Guest

    My PLL can not lock. I am using an Xor gate as the PD. And the VCO is
    cross coupled VCO. Now the control voltage is in the tuning voltage
    range of VCO, but it is an oscillation the same frequency as the
    output of the PD. It should be a DC voltage when the PLL is locked.
    What can be the problem? Thanks!
     
  2. Jim Thompson

    Jim Thompson Guest

    And your loop filter is what?

    ...Jim Thompson
     
  3. maxfoo

    maxfoo Guest

    disconnect the Vtune line and connect a power supply to the vco. then monitor
    the loop filter output on a scope and see if the voltage switches at the tune
    freq...




    Remove "HeadFromButt", before replying by email.
     
  4. Simon

    Simon Guest

    Sounds like you missed out the low pass filter between PD and VCO.
     
  5. cici

    cici Guest

    I am using a RC low pass filter, which is followed by a source follower.
     
  6. Jim Thompson

    Jim Thompson Guest

    [snip]

    And where is your *zero*?

    ...Jim Thompson
     
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