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LC Resonator

Discussion in 'Electronic Design' started by redhat, Jun 27, 2005.

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  1. redhat

    redhat Guest

    is there any difference between using 2,3 or 4 element LC resonator?
    Does one of them has better Q for example?

    regards
     
  2. Joel Kolstad

    Joel Kolstad Guest

    If you like, but you have to be careful as to how you define your "Q"'s here.
    You can take several resonators with low "unloaded Q's" (just the ratio of
    their impedance to their loss if you model the loss as a series element) and
    end up with a circuit that has an overall greater Q (sometimes called "loaded
    Q"). This happens because what multiple resonators are typically used for is
    to provide steeper skirts (transition bands) on a filter's response, and while
    there's no "magic" going on (using lots of cruddy, low Q resonators results in
    a filter that has lots of loss overall!), by virtue of the value Q is being
    defined in such a case (the center frequency divided by the -3dB bandwidth)
    you can end up with a higher Q than the original unloaded Q's.

    In general, more resonators give you more degrees of freedom to play with the
    shape of a filter's response. This is typically used to provide greater
    selectivity, but can also be used to counteract having to work with low Q
    resonators, building "fancy" filters that, besides, say, some "standard" shape
    such as Butterworth or Chebyshev, have an additional transmission zero or two
    dropped in at some additional frequency, etc.

    ---Joel Kolstad
     
  3. doug dwyer

    doug dwyer Guest

    Do you mean for a filter or an oscillator?
    I investigated the use of a toko ? or was it murata 400MHz two section
    helical filter as a resonator for a narrow band (10MHz) VCO.
    There did seem to be advantages.
    The filter cores could be adjusted to give linear freq/voltage .In
    response to voltage on an external varicap .
    Loss was low over the frequency range and measured ssb noise was state
    of the art 20 years ago
     
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