Question on CMRR

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

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

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
5,444
1,075
Deleted Deleted

Last edited: Jan 29, 2010
3. MikeML AAC Fanatic!

Oct 2, 2009
5,444
1,075
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...