Principles of Transistor Circuits, 9th Edition

Chapter 5

Common-collector and common-drain amplifiers (emitter and source followers)

Common-collector amplifiers

Introduction

The fundamental circuit of a common-collector amplifier is given in Fig. 5.1(a) in which R_s represents the resistance of the signal source and R_l represents the load resistance. For simplicity, bias sources are omitted from this diagram. In Fig. 5.1(b) the transistor is represented by an equivalent network of resistances r_e, r_b and r_c together with a voltage generator of e.m.f. αr_ci_e where i_e is the alternating current in the emitter circuit. If the base current i_b and emitter current i_e are both shown acting in clockwise directions as in Fig. 5.1(b), then the current in the common-collector resistance r_c is the difference ...