Designing Frequency-Dependent Impedances?

Discussion in 'Computer Information' started by Diego Stutzer, Feb 19, 2004.

  1. Hi,
    Every one knows, that e.g. a simple RC-parallel circuit has a
    frequency-dependent impedance-characteristic (Absolute Value) - the
    impedance (Abs) raises as the Frequency approaches zero. As a formula: Zin
    = 1/(1/R + i w C) , where i ist the imaginary number and w the frequency.

    Now the hard part. How does one create an Impedance, which decreases
    "slower", for frequencies close to zero but then decreases "faster" for
    higher frequencies, than the simple parallel RC-Circuit?
    Is there some kind of procedure like the one for syntesizeing LC-Filters
    (Butterworth, Chebychev,..)?

    Simply increasing C does not really help, because this equals a factoring of
    the frequency.
    Increasing R does not help as well, as it seems.


    I hope one of you cracks can help me out.
    So far, thanks for reading.
    Diego Stutzer
    Diego Stutzer, Feb 19, 2004
    #1
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  2. Diego Stutzer

    CWatters Guest

    http://www.amazon.com/exec/obidos/tg/detail/-/075062986X/102-4757360-8277714?v=glance


    "Diego Stutzer" <> wrote in message
    news:...
    > Hi,
    > Every one knows, that e.g. a simple RC-parallel circuit has a
    > frequency-dependent impedance-characteristic (Absolute Value) - the
    > impedance (Abs) raises as the Frequency approaches zero. As a formula:

    Zin
    > = 1/(1/R + i w C) , where i ist the imaginary number and w the frequency.
    >
    > Now the hard part. How does one create an Impedance, which decreases
    > "slower", for frequencies close to zero but then decreases "faster" for
    > higher frequencies, than the simple parallel RC-Circuit?
    > Is there some kind of procedure like the one for syntesizeing LC-Filters
    > (Butterworth, Chebychev,..)?
    >
    > Simply increasing C does not really help, because this equals a factoring

    of
    > the frequency.
    > Increasing R does not help as well, as it seems.
    >
    >
    > I hope one of you cracks can help me out.
    > So far, thanks for reading.
    > Diego Stutzer
    CWatters, Feb 19, 2004
    #2
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  3. Diego Stutzer

    Tom Bruhns Guest

    If you think of it as a "filter", you may be able to find software
    that lets you specify values at frequencies, and will design a network
    for you. But if I understand correctly, you simply want an impedance
    whose magnitude is some value at some mid frequency, and drops above
    and below that. That's just a parallel LRC circuit. If you need the
    impedance to go to (or near) zero at some specific high frequency, you
    can put an LC series across the parallel LRC. Actually, you can do it
    by making the C an LC series instead. But then the impedance rises
    again beyond the LC series resonance.

    It can be a useful visualization to think of poles and zeros in the
    s-plane when trying to get to a circuit that gives you a specific
    impedance shape. You can readily see that some responses are not
    possible with a finite number of L/R/C components, though in general
    you can get the impedance magnitude you want at a set of distinct
    frequencies with a finite number of _ideal_ components. I'll bet
    there are some good s-plane pole/zero tutorials on the web.

    Cheers,
    Tom

    (Diego Stutzer) wrote in message news:<>...
    > Hi,
    > Every one knows, that e.g. a simple RC-parallel circuit has a
    > frequency-dependent impedance-characteristic (Absolute Value) - the
    > impedance (Abs) raises as the Frequency approaches zero. As a formula: Zin
    > = 1/(1/R + i w C) , where i ist the imaginary number and w the frequency.
    >
    > Now the hard part. How does one create an Impedance, which decreases
    > "slower", for frequencies close to zero but then decreases "faster" for
    > higher frequencies, than the simple parallel RC-Circuit?
    > Is there some kind of procedure like the one for syntesizeing LC-Filters
    > (Butterworth, Chebychev,..)?
    >
    > Simply increasing C does not really help, because this equals a factoring of
    > the frequency.
    > Increasing R does not help as well, as it seems.
    >
    >
    > I hope one of you cracks can help me out.
    > So far, thanks for reading.
    > Diego Stutzer
    Tom Bruhns, Feb 19, 2004
    #3
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