kerekuto
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I am trying to obtain the gain of a 2-stage op-amp, but it seems that the output resistance is far less than what i'm expecting. The output resistance is supposed to be the parallel combination of the output resistance of the pmos and nmos, right? in Results Browser, the gds value of the pmos is 2.21E-5 and for the NMOS is 1.94E-5. Therefore, I should be expecting an output resistance of around 24Kohms. In order to verify this, I am instantiating the op-amp in a testbench with the input terminals grounded, and an ac current source with magnitude of 1 A connected at the output. Measuring the voltage in an AC analysis should plot the output resistance of the opamp, but the magnitude is only 16.6Kohms. Is gds the right parameter to calculate the output resistance? Why am I getting such a big difference from what I'm expecting?
Thanks in advance!
Thanks in advance!