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Help: simulate CMRR of opamp

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rogerqin

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A method of simulating CMRR of opamp directly is provided in Allen's book. The circuit configuration is as figure.
The equations are:
vout = (vp-vn)*Av+0.5*(vp+vn)*Ac
vp = vcm
vn = vout+vcm
so we have, (1+Av-0.5*Ac)*vout = vcm*Ac.
and vout/vcm = Ac/Av = 1/CMRR

The spice netlist is listed as follows:
vcm1 vp 0 1.27 ac=1
vcm2 vn vout 1.27 ac=1
.probe v(vp,vout)

But the simulation result is not correct.
Please help me to check it, thanks!

 

Please help me to check it, thanks a lot.
 

I had simulated my amp with the method .then I got the right result.
U should check ur opamp circuit .U can find the reason.

Thanks
 

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