Questions about the VCVS filter

Discussion in 'General Electronics Chat' started by Kesbin, Feb 12, 2009.

  1. Kesbin

    Thread Starter New Member

    Dec 9, 2008
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    Attached are two circuit example. The VCVS filter is on the left hand side. What the effect would be if resistor R4 had been replaced by a capacitor.
    The damping factor is affected by the resistors R3,R4, as DF= 2-(R3/R4). Can anyone explain the working properties of right hand side circuit?Thanks!
     
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  2. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    Are you sure you have the right hand circuit correct?

    You haven't just replaced R4 with a capacitor; it's connected differently. Shouldn't one end of the capacitor go to ground?
     
  3. Audioguru

    New Member

    Dec 20, 2007
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    The writing of the parts values is so small in the schematics that I can't see them. Please make the values readable and save the image as a very clear GIF or PNG file type instead of as a fuzzy JPG file type.
     
  4. Kesbin

    Thread Starter New Member

    Dec 9, 2008
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    I have updated the image. The end should not go to the ground. That's the point i confused. Please help me. Thanks...
     
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  5. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    In the left hand circuit, R3 and R4 affect the feedback to the - input.

    In the right hand circuit, if the opamp is assumed to be ideal, with infinite input impedance on both the + and - inputs, then R3 and C3 will have no effect whatsoever on the behavior of the circuit. It will be as if the output is connected directly to the - input.

    In reality, they will have an effect, but you will have to determine the input impedance and bias current at the - input, perhaps from the data sheet, before you can analyze the true effect of R3 and C3.
     
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