op-amp differentiator circuit

Discussion in 'Homework Help' started by swathin, Nov 6, 2008.

  1. swathin

    Thread Starter New Member

    Nov 6, 2008
    3
    0
    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
     
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    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.
     
  3. swathin

    Thread Starter New Member

    Nov 6, 2008
    3
    0
    thanks for the help
     
Loading...