op-amp differentiator circuit

Thread Starter

swathin

Joined Nov 6, 2008
3
what are the values of Rf,Cf,Cin to get o/p voltage more than 2.5v for a change of .5mv per micro sec
 

Ron H

Joined Apr 14, 2005
7,012
For a capacitor, I=C*dv/dt
rearranging,
(1) I/C=dv/dt
Vout=I*Rf
rearranging,
I=Vout/Rf
substituting into (1),
Vout/(Rf*Cin)=dv/dt
Rf*Cin=Vout/(dv/dt)

You don't need Cf. You should put a low-value resistor in series with Cin to keep the op amp stable (so it won't oscillate).
I would choose Rf in the range 10k - 100k. The series stabilizing resistor can be about Rf/100.
The op amp inverts, so a positive input slope will yield a negative output voltage, and vice-versa.
 
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