OPAMP CMRR Simulation Topology

[020170]

simulation ac dc cmrr

I read following link.



V1 and V2 has no DC value and V1 and V2 has AC 1

In hspice syntax, this can be written like this (Fig 1.)

V1 INP GND DC 0 AC 1
V2 INN OUT DC 0 AC 1

I don't understand why this topology was used to simulation CMRR.

Instead of this simulation way, I was used this method to simulate CMRR


1. First, get Differential Gain

X_OPAMP INP INN OUT VDD GND
V1 INP VCM DC 0 AC 1
V2 INN VCM DC 0
VCM VCM GND DC 1

2. Second, get Common Gain

X_OPAMP INP INN OUT VDD GND
V1 INP VCM DC 0
V2 INN VCM DC 0
VCM VCM GND DC 1 AC 1


In the end, 1 - |2| = CMRR

Is this method correct?

thanks.

 

[akhilrathore]

cmrr simulation -that

HI,
The difference in db will give u cmrr... u can check with ALLEN HOLBERG second edition pp-325. for all simulation set up u need for an opamp.