Introduction of Multistage Amplifiers and Differential Amplifier

MULTISTAGE AMPLIFIERS AND DIFFERENTIAL AMPLIFIER

INTRODUCTION

Single stage transistor amplifiers are inadequate for meeting most design requirements. Hence we use more than one amplifier stage.

In multistage amplifier, the output of one stage is fed as the input of the next stage. This type of connection of amplifiers is called cascading.

Definition

Multistage amplifier is defined as the amplifier in which more than one amplifying stage is used to achieve greater voltage and power gain.

Fig.3.2 shows the multistage amplifier connected in cascade

Gain

The voltage gain of a multistage amplifier is equal to the product of the gains of the individual stages. If A_V1, A_V2, ... ,A_VN are the gain of individual stages, then the overall voltage gain is

A_V = A_V1 . A_V2 … A_VN

In decibels,

Overall current gain,

Requirements of multistage amplifier

i. Impedance matching

ii. Gain should be high

iii. Large bandwidth