Analysing all pass filter

Thread Starter

andy24691

Joined Nov 25, 2010
42
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.

cheers
 

Ron H

Joined Apr 14, 2005
7,063
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
 

Thread Starter

andy24691

Joined Nov 25, 2010
42
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.
 

Ron H

Joined Apr 14, 2005
7,063
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.
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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