Analysing all pass filter

Discussion in 'Homework Help' started by andy24691, Jan 5, 2011.

  1. andy24691

    Thread Starter Member

    Nov 25, 2010
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    0
    I have been asked to derive the gain equation and phase angle equation for the all pass filter circuit shown. After going through it several times I have got a gain equation of (1/jwcR1+1)-1. This does not seem right to me. As for the phase angle equation I am pretty much clueless. Any help would be greatly appreciated.
    [​IMG]
    cheers
     
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    656
    Close. You forgot that the gain from the +input is multiplied by 2, due to the feedback.
    Also, you need parentheses around the denominator (jwCR1+1) of your first term.
    So your equation needs to be Av=2*1/(jwCR1+1)-1
     
  3. andy24691

    Thread Starter Member

    Nov 25, 2010
    42
    0
    I have gone through it again and I know have come to:
    vout/vin = 1 - [2/ 1 + jwcR1]. Or should it be -vout/vin?

    Also could you tell me about the phase angle equation as well please.
     
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    656
    Yes, your sign is wrong. The equation I posted is correct. And you still don't know how to use parentheses correctly.
    Have you been taught how to calculate amplitude and phase response?
     
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