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OPA858: PSpice Noise Simulation

Part Number: OPA858
Other Parts Discussed in Thread: THS4541

Hello all,

I am trying to simulate the noise of the following circuit. The circuit has a transimpedance amplifier (TIA - OPA858) and a fully differential amplifier (FDA - THS4541). However, I am not getting the expected results.

This is the configuration profile window. Basically, I want to measure the noise at the output of both circuits. Although in this window, I am only measuring the noise at one of the FDA outputs.

So, after running the simulation, I got the results below. The simulation gives me a maximum noise value of 22fV/sqrt(Hz) which I believe is too small for what I expected.

Since only the total noise of the resistors appear on the available traces, I believe that the Op-Amp noise isn't being simulated.

So, how can I insert the Op-Amps noise in this simulation, in order to have a proper noise simulation?

Thank you in advance.