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Cascade Sallen Key Filters

Discussion in 'Electronic Design' started by panfilero, Jul 18, 2013.

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  1. panfilero

    panfilero Guest

    I was wondering, if you cascade two identical low pass sallen key filters one after another, do you keep the same same cut-off frequency of the singlesallen key filter? I'm thinking yes, that you just increase your poles, from a 2 pole ystems to a 4 pole system, but I'm not sure, I used the following website to come up with my single stage, at 140Hz....

    http://sim.okawa-denshi.jp/en/OPstool.php


    much thanks!
     
  2. Wimpie

    Wimpie Guest

    El 18-07-13 20:34, panfilero escribió:
    Hello,

    The overall -3 dB frequency for the two-stage will be the -1.5 dB
    frequency of a single stage (you add two).

    If you want the same overall -3 dB (or other value) bandwidth, you
    need to displace the frequencies somewhat (one down and one up). You
    will get better passband flatness and better out of band rejection.
     
  3. What everyone else said.
    If you have H&H's Art of Elec. then there is a small table in the filters section that gives you some of the 'Gains' and frequencies for various filter types.

    George H.
     
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