how to calculate load capacitance?

calculating load capacitance

attached is a circuit diagram, in which A1, A2 are bipolar amplifiers.
Since the load capacitance value of A1 is needed when desinging frequency response compensation, so would like to konw how to calculate this load capacitance ?

thanks!

how to calculate load capacitance

Basically one needs input capacitance of A1 amplifier and input capacitance of A2 amplifier. Depending on stuation A1 's output capacitance may also be needed (A1 output impedance need also be known for complete AC response).

If A1 and A2 are discrete than one can try to get approximate values from data sheets.

If A1 and A2 is designed by you than as designer you extract capacitances from spice netlist at a given bias condition. If bias change than capacitances are nonlinear and will change with bias point. But one can approximately take the capacitances at DC bias point, assuming AC signal at input is small. Than one can take the bias point extremes ad DC+/- AC at input and get bias points at those biases to check variation. Spice run will account capacitance changes anyway.