Small signal model for op amp
This circuit should do the job. 







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A2 is a transconductance amplifier (Voltage-IN, Current-Out). 

So we have a voltage-controlled current source (VCCS). 

And for the current source, Ro is in parallel with the current source. 

Ro in series with the current source will have no effect on the output current (source current). Because in this case, we need a current divider.

Ro represents the "losses" in the current.    







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