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Gm-C Integrator design

  1. Sep 15, 2010 #1
    Gm-C Integrator design...........

    Dear all,

    I have been asked to design Gm-C continuous time integrator with no rigid specifications. I have used a two stage OTA with 46dB gain and applied a capacitor at the end as integrating element. But the circuit is merely acting as an amplifier and not integrator. It does not convert square wave into triangular..... What modifications do i need to bring? Circuit schematic attached....

    http://images.elektroda.net/32_1284460009.jpg
    the circuit quite well acts as a low pass filter after installation of capacitor at the end...I believe just a capacitor at the end cant transform an amplifier into integrator......
     
  2. jcsd
  3. Sep 15, 2010 #2
    Re: Gm-C Integrator design...........

    I believe you need a large series resistor R between the amplifier and capacitor C, such that RC is long compared to the integration time. For 1% linearity, RC>=100 x square wave integration time.

    Bob S

    [added]
    Suppose after t=0 for square wave input, Vout(t) = V0[1-e-t/RC]

    Then dVout(t)/dt = [V0/RC]e-t/RC

    To achieve integration linearity of 1% (meaning dVout(t)/dt = constant) , e-t/RC >= 0.99 for all t
     
    Last edited: Sep 15, 2010
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