Hi !
I am trying to simulate the CMRR of the INA126P instrumentation OP Amp with no success. According to the datasheet, I should obtain a CMRR of 95 db around 10Hz, regardless of the gain. However, when simulating, this value change and is lower than the datasheet. Am I doing something wrong? Here is my test circuit.
Regards.4336.INA126Test.TSC
Sylvain,
The problem with your simulation of INA126 CMRR is that you are not accounting for the gain of the circuit. By defination, CMRR=VG1/Vos. Since Vos=VM1/Gain, therefore, CMRR=20*log(VG1/Vos)=20*log(Gain*VG1/VM1).
Doing so, will result in the family of CMRR curves that very closely match PDS graphs, including CMRR of 95dB below 10Hz for all gains - see below.
