I have designed a circuit in Cadence Virtuoso. As a first step, I used all the transistors without fingers (i.e. each transistor is a single transistor). Once the circuit satisfied all the requirements I wanted (dc gain, location of the poles, slew rate and so on) I decided to use fingers for each transistor in order to realize the stick diagram. To my astonishment, after using fingers, the dc analysis was completely different with respect to the original circuit: the dc voltages at each node were considerably different with respect to the original circuit.
Question: I know that fingering is used to reduce parasitic capacitances. Anyway, since a capacitor is an open circuit in dc, theoretically nothing should change as far as regards the dc analysis. Why then did Cadence give completely different results in dc when I converted my original circuit into the "fingered" version?
Here the circuit without fingers:
It is a two stages op-amp in open loop configuration (frequency compensation network has been omitted). If now I put 9 fingers for PM21, I get the following dc result:
As you can see, the output dc voltage has changed!