parasitic capacitance

Dear Everybody! I developed a new vienna rectifier based PMG generator rectifier solution. My vienna rectifier input is connect to the PMG generator across the 3 boost inductor. I developed the control algorithm in matlab simulink, and I recognized that the PMG star point (N) and the vienna...

So here: I assume each transistor has some sort of parasitic capacitance and that adds up into the non inverting terminal of the op amp? Why do those parasitic capacitances appear and how can i reduce them? And in this case: These capacitances appear because of Q4/Q3... ? They depend on...