6.1 Analog electronics lecture 2_partb_bjt configurations & Modes

Analog Electronics Lecture 2_PartB_BJT configurations&modes

Key words;CE,CC&CB BJT;

Abstract: This describes three circuit configurations, four modes of operation and five schemes of biasing;

BIPOLAR JUNCTION TRANSISTOR

FOUR MODES OF OPERATION

THREE CIRCUIT CONFIGURATIONS

1. COMMON BASE CONFIGURATION

1. COMMON EMITTER CONFIGURATION

1. COMMON COLLECTOR CONFIGURATION

The Figure of Common Collector Configuration is not given here. An emitter follower is an example of Common Collector Configuration. In Emitter Follower the collector is directly connected to the positive of the battery and under incremental analysis or under small signal analysis the battery is considered short circuited.Hence under signal condition, collector is effectively shorted to ground. Hence Emitter Follower is a Common Collector Configuration.In Emitter followr , input is at base but output is at emitter.The voltage at emitter follower follows the voltage at the input namely the base. Hence the voltage gain is Unity but current gain is almost 100. It can deliver a large current. Hence it is a Buffer and used for driving the load after the pre-amplifier.

TYPES OF BIASING SYSTEM USED

(1)Two battery biasing:

The 3 circuit configurations shown in the previous page are the examples of this biasing.

(2)Fixed Bias:

This type of biasing system offers poor stability because it has negative feedback..

(3)Potential Divider Bias:

This type of biasing also offers poor stability because this also has no negative feedback.

(4)Self Biasing:

This type of biasing system offers high stability because of current series feed-back.

(5)Widlar Biasing:

The above types of biasing systems are used normally for discrete circuits. But this type of biasing is used for IC technologies. It offers high stability because of voltage shunt feed-back.This is also known as collector to base feed-back.