Hi everyone, I'm designing a Fully Differential Folded Cascode OPAMP; to verify the input linearity range and the circuit well behavior, I plot the Vo+ Vo- and Vo-differential vs. the differential input voltage.

In the graph, I can appreciate a linear response in the range of +-80uV; I thought that the non-linearity was due to a transistor not working in saturation, so I also graphed the region of operation of each transistor and saw that all were in saturation in the range of +-80mV. So I don't understand the non-linearity from 80uV to 80mV.

Some can help me, please. Thank You.
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