Double stage of first order low-pass filter

Discussion in 'Homework Help' started by jenson, Dec 8, 2011.

  1. jenson

    Thread Starter New Member

    Jun 2, 2011
    1
    0
    Hi,

    What is the purpose for using double stages of the low-pass filter as the firgure shown below and is there any improvement in filtering when using double stages of the low-pass filter? Thanks.

    Jenson

    [​IMG]
     
  2. crutschow

    Expert

    Mar 14, 2008
    12,993
    3,227
    Two first-order stages have double the rolloff outside the passband (12dB/octave instead of 6dB/octave).

    But the corner rolloff is very soft for two such stages in series so it's not often used in practice. It's much better to use an active two-pole filter (such as a Butterworth) where the feedback gives a sharper rolloff at the corner.
     
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