BJT Circuits

Summary

The (NPN/PNP) Bipolar Junction Transistor (BJT) is a three‐terminal device formed from two P‐N junctions (like diodes) which share a common (P/N‐type) semiconductor and is widely used for various purposes including amplification and switching. This chapter deals with several configurations of BJT amplifier, i.e. the common‐emitter (CE) amplifier, the common‐collector (CC) amplifier (called an emitter follower), the common‐base amplifier, and cascaded or compound multistage amplifier. It then discusses the diode‐transistor logic NAND gate, transistor‐transistor logic NAND gate, and emitter‐coupled logic OR/NOR gate. Next, the chapter shows how a CE amplifier with a desired voltage gain or CC amplifier with a desired input resistance can be designed, i.e. how the values of resistors constituting the circuits can be determined to satisfy the design specification. It further describes the BJT amplifier frequency response and the BJT inverter time response.