Question on CMRR

Discussion in 'Homework Help' started by shiva bharadwaj, Jan 29, 2010.

  1. shiva bharadwaj

    Thread Starter Member

    Sep 29, 2008
    19
    0
    Hi ,
    i have a question on opamps
    CMRR was given,
    the question was to find the output voltage,,,
    CMRR=60db
    it is a closed loop amplifier
    R1=R2=1k
    Rf=Rg=100k
    [​IMG]

    the voltage at non inverting terminal and inverting terminal are same and equal to one volt
    V+=V-=1

    so input differential mode voltage,Vd=0
    input common mode voltage,Vc=1
    can you please tell me how to find out the output voltage?
     
    Last edited: Jan 29, 2010
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Deleted Deleted
     
    Last edited: Jan 29, 2010
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    This is obviously homework: I do not just provide answers lest you learn nothing.

    CMRR results from the fact that Rf/R1 ≠ Rg/R2. The two ratios are not exactly the same. This could be due to the tolerance of the resistors. The op-amp itself can exhibit some non-ideal behavior.

    Someone already told you that the effect of the imperfections cited above results in the output voltage containing an error which puts it within a -60db band of what the ideal circuit should be.

    I'll let you do the math...
     
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