Why a tiny feedback capacitor can wreck your amplifier's high-frequency response.
Every inverting voltage amplifier — a common-source MOSFET stage, a common-emitter BJT stage, an inverting op-amp — has a small capacitance connecting its output back to its input. Sometimes it's an unavoidable parasitic (the gate-drain capacitance Cgd of a MOSFET, the base-collector capacitance Cbc of a BJT); sometimes it's deliberately added. Either way, a capacitance of just a few picofarads sounds too small to matter. It isn't. Because the amplifier inverts and amplifies the voltage across that capacitor, the capacitor has to do far more work than its tiny physical size suggests — and from the input's point of view, it behaves as if it were dramatically larger.