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Active low pass

  1. Jun 1, 2009 #1
    What advantage does an active low pass have over chaining passive low passes?

    Everyone seems to warn me about dc drift and such things, but there must be some reason why active low passes were invented.
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  3. Jun 1, 2009 #2


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    Active filters have gain.
  4. Jun 1, 2009 #3


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    They are comparatively inexpensive. After a certain number of poles a stage of gain may be required so why not go active to start with?
  5. Jun 1, 2009 #4


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    Also, if you caluclate the component values for a passive low-pass filter with a cut-off of about 40 Hz or so you will realize that active filters have another advantage.

    Note that active filters have their drawbacks as well. The most obvious being that there is always a risk that you introduce additional noise in the circuit due to the component in the filter (e.g. op-amps can be quite noisy).
  6. Jun 1, 2009 #5


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    The main advantage of active filters is that they don't need COILS.

    COILS are a pain to wind and measure, or expensive to buy, and they are also quite bulky for the air wound ones.

    Active filters have to have a power supply, but they only have resistors and capacitors apart from the op amps. And, they can have gain or at least not lose any signal amplitude for the wanted part of the spectrum..
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