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dielectrics and distortion; modeling of ceramic capacitors

Discussion in 'Electronic Components' started by Christoph Loew, Apr 8, 2005.

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  1. I've been using Murata's GRM series capacitors with X7R dielectric
    for power supply bypassing in digital circuits and am now looking
    into using the same capacitors in a Sallen-Key bandpass filter for
    audio signals.

    The TI application report "Analysis of the Sallen-Key Architecture"
    suggest using NP0 and avoiding Z5U while stating "X7R is OK in a
    pinch". If I understand the matter correctly, the X75 and Z5U are
    worse than NP0/C0G when it comes to aging, stability of capacitance
    over temperature and changes of capacitance depending on applied
    voltage since the X75 and Z5U are ferroelectric.

    The last one is supposed to make X75 and Z5U a bad idea for audio
    circuitry sice they will add "a lot" of distortion to the signal
    (I've seen a diagram showing 100 times the TDH when measured against
    C0G in a simple RC highpass).

    So my questions are :

    Is the a recommended book that covers these details of ceramic
    capacitors (physics and chemistry of the dielectric and the effect
    on component behaviour)?

    What effect is responsible for the distortion of a sine wave
    applied to or passing through a capacitor ? Is it only the change of
    capacitance with voltage ? Again, is there a recommended book that
    covers this ?

    How can the adding of distortion be modeled in e.g. LTSpice - the
    default capacitor model only covers ESR,ESI,EPR and EPC ?


    any hints appreciated,

    Chris
     
  2. Hi K ceramics achieve their performance by doping with piezoelectric
    ceramics. It is common to hear them click if hit with a high level
    rectangular pulse at an acoustic rate.
    NPO are now available up to 1U or so by means of very thin dilectric
    layers but expensive.
    The feed material for the best plastic is being discontinued by its
    German chemicals co.
    A great series of articles over the last 3 years in electronics world
    giving circuits to measure and compare capacitor distortion.in Hi Fi
    situations.
     
  3. Articles by Cyril Bateman
     
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