Module 2: Part 2

Basic BJT Amplifiers

Learning ObjectivesAfter studying this module, the reader should have the ability to: Explain graphically the amplification process in a simple bipolar

amplifier circuit. Describe the small-signal hybrid-p equivalent circuit of a bipolar

transistor and to determine the values of the small-signal hybrid-p parameters.

Apply the small-signal hybrid-p equivalent circuit to various bipolar amplifier circuits to obtain the time-varying circuit characteristics.

Characterize the small-signal voltage and current gains and the input and output resistances of a common-emitter amplifier.

Characterize the small-signal voltage and current gains and the input and output resistances of an emitter-follower amplifier.

Characterize the small-signal voltage and current gains and the input and output resistances of a common-base amplifier.

Apply the bipolar small-signal equivalent circuit in the analysis of multistage amplifier circuits.

(a) Bipolar transistor inverter circuit; (b) inverter transfer characteristics

Common-emitter transistor characteristics, dc load line, and sinusoidal variation in base current, collector current, and collector-emitter voltage

Base current versus base-emitter voltage characteristic with superimposed sinusoidal signals

A simplified small-signal hybrid- equivalent circuit for the npn transistor

Expanded small-signal model of the BJT, including the Early effect, for the case when the circuit contains the (a) transconductance and (b) the current gain parameters

Basic data sheet for the 2N2222 bipolar transistor

A bipolar circuit with an emitter resistor, a voltage-divider biasing circuit, and a coupling capacitor

The small-signal equivalent circuit with an emitter resistor

Emitter-follower circuit

Small-signal equivalent circuit of the emitter-follower

Basic common-base circuit

(a) Simplified hybrid- model of the npn transistor and (b) small-signal equivalent circuit of the common-base circuit