History
- 1920s–1930s — Negative feedback. Harold Black's Bell Labs work showed how very high amplifier gain could be traded for predictable closed-loop gain, lower distortion, and wider bandwidth.
- 1940s — Analog computers. Vacuum-tube amplifiers with resistor and capacitor networks performed addition, subtraction, integration, and differentiation.
- 1947 onward — Transistors. Solid-state amplifiers removed heaters and greatly reduced size and power.
- 1950s–early 1960s — Modular op-amps. Precision transistor amplifiers were sold as modules before complete monolithic IC op-amps were practical.
- 1963 — µA702. Bob Widlar at Fairchild produced an early commercially important monolithic op-amp.
- 1965 — µA709. Widlar's 709 became a widely used early IC amplifier, although it required external compensation.
- Late 1960s — 741 era. Internally compensated designs made op-amps far easier to apply. The 741 became one of electronics' most recognizable ICs.
- 1970s — JFET and single-supply families. JFET inputs provided very high input impedance, while LM324/LM358-style devices helped make single-supply analog design routine.
- 1980s–1990s — Specialization. Low-noise audio, precision, chopper, high-speed, micropower, and low-offset families multiplied.
- Modern era. Op-amps now range from nanopower sensor amplifiers to GHz-class high-speed devices, zero-drift precision amplifiers, fully differential ADC drivers, and power op-amps.
Why the op-amp endured
The physical world is analog. Sensors, audio, motors, power supplies, and converters still need accurate analog gain, buffering, comparison, and filtering even when the final system is digital.