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Decoupling Capacitors

Discussion in 'General Electronics' started by Sanjayan Vinayagamoorthy, May 13, 2004.

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  1. Hello,

    I was told that there were two uses for decoupling capacitors. The one
    that I know of is when there is a transition in the IC in TTL or CMOS
    logic, there is a could be a lot of current consumed, which in turn
    would cause spikes in the power supply lines. This is avoided by
    placing capacitors on those power lines.

    However I am not sure of another use. I know of one other example,
    especially used to make sure sure that DC bias points from one common
    source amplifier are not passed to another. I.e. one would you
    resistors to bias the gate/base of a transistor and then a capacitor
    from the base to the ac input. Therefore the DC voltage of the ac
    signal doesn't affect the biasing conditions of the amplifier. I am
    not sure if this capacitor is also called a decoupling capacitor or is
    it something else? Like a Bypass capacitor instead?

  2. Rich Grise

    Rich Grise Guest

    Actually, in that app, it's called a coupling capacitor. It couples the
    signal from one stage to the next, and blocks the DC. So, it is sometimes
    (or was a thousand years ago) called a "DC blocking" capacitor.

    Hope This Helps! :)

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