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Two-stage pass-band filter - Overall gain

  1. Dec 14, 2012 #1

    JJBladester

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    Gold Member

    1. The problem statement, all variables and given/known data

    When calculating the overall gain of a two-stage pass-band filter, can one simply add the gain from the high-pass filter (R1/C1) to the gain from the low-pass filter (R2/C2)?

    pass-band-filter.JPG

    2. Relevant equations

    N/A.

    3. The attempt at a solution

    For example, if the gain from the high-pass filter was -2dB and the gain from the low-pass filter was -5dB, is the overall gain -7dB?

    My book does not go into an explanation on how this works. I may just set up a test circuit in MultiSim to get a general idea of the output gain w.r.t. the individual gains of the high- and low-pass filters.
     
  2. jcsd
  3. Dec 14, 2012 #2

    gneill

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    Staff: Mentor

    In general, no, as the input impedance of the second stage will affect the first stage's response, while the output impedance of the first stage affects the second's.

    However, if components are selected carefully to minimize the loading, then adding the gains will give a good approximation. For example, make the input impedance of the second stage about 10x that of the output impedance of the first stage.
     
  4. Dec 14, 2012 #3

    NascentOxygen

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    Staff: Mentor

    See https://www.physicsforums.com/showthread.php?t=652403
     
  5. Dec 15, 2012 #4

    JJBladester

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    Gold Member

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