How do the internal transistor configurations in op-amps affect their gain and stability?

Internal transistors in an op‑amp form a differential input pair that sets the basic transconductance; higher transconductance gives a larger open‑loop gain because the differential current can swing more for a given input voltage. The next stage, often a common‑collector or emitter follower, buffers that current into a low‑impedance output, and its internal resistance and transistor gain also add to the overall voltage gain. Stability is governed by how quickly these internal stages respond; if the transistors create a fast pole, the op‑amp can oscillate, so designers insert compensation capacitors that slow the response and increase phase margin. For example, a two‑stage op‑amp with a 10⁶ transconductance and a compensation capacitor of 1 pF will have a high open‑loop gain but a stable 45° phase margin, preventing oscillation. Thus, the transistor arrangement directly controls how much voltage the op‑amp can amplify and how smoothly it can do so without ringing.