Build an op amp with three discrete transistors

摘要

You can use three discrete transistors to build an operational amplifier with an open-loop gain greater than 1 million (Figure 1). You bias the output at approximately one-half the supply voltage using the combined voltage drops across zener diode D,, the emitter-base voltage of input transistor Q_1, and the IV drop across 1-MΩ feedback resistor R_2 Resistor R_3 and capacitor Cl form a compensation network that prevents the circuit from oscillating.