Simulation

Operational Amplifier in LTSpice

What’s actually inside an op-amp? I spent a few months teaching myself, then built one from scratch out of individual transistors in LTSpice to find out.

• Learned and built every stage myself: differential pair, current mirrors, and a Darlington output stage
• Tested it by stepping the feedback resistor through four values and checking the gain against theory
• Measured gain matched the predicted Rf/Rin ratio almost exactly, even at ×1000