OPA328: Difference in CMRR Vs Frequency plots in TINA_TI and PSPICE_for_TI

Hello Vijaymahantesh,

The simulation is forward gain, acceptance. Rejection (CMRR) is the inverse of forward gain. In dB units, this is simply opposite polarity. 

Oh Okay, So in post processing I have to add 1/Vout(s) for CMRR. Thank you

But I have a question on why TINA_TI and PSPICE_for_TI gives 2 different results for the same simulation

Vijaymahantesh,

The DC operating point for output is at the negative supply rail (potentially non linear circuit). Try setting it inside the operating range. Add a DC difference input voltage or change V- voltage from 0V to -0.5V

Hello Ron,

"Add a DC difference input voltage ", Do you mean as shown below?

result of above circuit is as below

"or change V- voltage from 0V to -0.5V", (but this is RRIO precision opamp)

result of above circuit is as below

still in the high frequency region, results from PSPICE_for_TI is still not as it showed in TINA_TI

Thank you

Are you sure TINA and spice use the same model? Online there are multiple choices that may or may not be matching.

At high frequency the op amp won't keep up, the input signal through the feedback can drive the output directly. Expect variance way up there between different model revisions, different simulation engines, and between simulation and reality.  

In TINA Ti I have used the model present in "OPAx328 TINA-Ti Reference Design" (SBOMC38.TSC). While in PSPICE_for_TI, there is a model present in the part search, so I have used that. It seems both (TINA_TI and PSPICE_for_TI) seems to give different results for CMRR and PSRR frequency response.

Vijaymahantesh,

Can you share the exported data tables? I want to combine them to see the differences more clearly.  If the high frequency data matters, then C1 and C2 will have to be highly matched (easy in sim, improbable in reality) otherwise none of simulations results mean anything.

Can you share the two simulation files?