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 what?

 

Parasitic capacitance is circuit theory speak for field theory EM geometry of devices and interconnects. Those electric fields that exist between the parts of an electronic component or circuit is modeled as a Parasitic capacitance for easy computation.
https://rahsoft.com/2021/04/21/parasitic-capacitances-in-mos-transistor/

 

https://asic4u.wordpress.com/2019/11/17/reducing-parasitics-in-finfet-layouts/