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Substituting crystal for ceramic resonator.

Discussion in 'Electronic Design' started by Ian Stirling, Oct 8, 2005.

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  1. Ian Stirling

    Ian Stirling Guest

    I'm considering substituting a crystal for a ceramic resonator in a
    USB project (12Mhz).
    I have a few of these to make, so using the 12Mhz crystals I already have
    would be nice.
    Is this possible simply by altering the capacitive loading?
    Anything to watch out for?
    As I understand it, this may overdrive the crystal. But I don't especially
    care about frequency - 500ppm is fine, so is this an issue?
    Many thanks.
     
  2. PeteS

    PeteS Guest

    Are you trying to replace a resonator that the mfr expects to be on the
    pins of the device?

    Resonators and crystals have somewhat different operational modes, and
    the on-chip oscillator may not work with a crystal. If you have the
    details of the onboard oscillator (from the datasheet or perhaps in an
    app note), I would run it by the group (perhaps on a.b.s.e).

    I wanted to do this (on a USB hub device), but my crystal supplier
    stated quite unequivocally that the onboard oscillator required a
    ceramic resonator and they had no crystal that would work as is. By
    altering the loading and perhaps providing a DC feedback path (100k or
    so in parallel with the crystal) things *might* work, but it will
    depend on the implementation details of the oscillator.

    Cheers

    PeteS
     
  3. Pooh Bear

    Pooh Bear Guest

    What's the oscillator ?

    Most chips will use resonators or crystals equally happily but the capacitive
    loading may have to be altered ( see the crystal / resonator mfr's datasheet
    and the semi makers too ).

    Graham
     
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