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Sylhet International University

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Welcome to our presentation

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Bipolar Junction Transistor (BJT)

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Rudela Sourav ChowdhuryElectronics & Communication Engineering (3-1)

Sylhet International University.Shamimabad, Sylhet-3100.

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Contents Introduction

Types of Bipolar Junction Transistor (BJT)

BJT configurations Common Base

Common emitter

Common Collector

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TranssistorA transistor consist of two pn junction formed by

sandwiching either p-type or n-type semiconductorbetween a pair of opposite types-

1) BJT

2)FET

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Bipolar Junction Transistors

(BJT) Transistor has two PN junction. One junction is forward

biased and other is reverse biased. The forward biasedjunction has a low resistance path and a reverse biased

junction has high resistance path. This transistor transfer asignal from a low resistance to high resistance .

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stors

npn pnp

E

B

C

E

C

CrossSection

CrossSection

B

C

ESchematicSymbol

B

C

B

E

SchematicSymbol

p n pn p n

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BJT Configurations Common Base

Common emitter

Common Collector

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Common Base configuration

The base is common to both input (emitter base) andoutput (collector base) of the transistor.

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Common Base ConfigurationInput Characteristics for a Common-Base

Amplifier

The following points may benoted from this characteristics

1) The emitter current IEincreases rapidly with smallincrease in emitter base voltageVBE . It means that inputresistance is very small.

2) The emitter current is almostindependent to collector base

voltage VCB.

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Output Characteristics for a Common-Base Amplifier

Satura

tion

Region IE

IC

VCB

Active Region

Cutoff

IE = 0

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Common Base Configuration

Three regions of operationActive

Operating range of the amplifier.

CutoffThe amplifier is basically off. There is voltage but

little current.

Saturation

The amplifier is full on. There is little voltage but lots ofcurrent.

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COMMON-EMITTER

CONFIGURATIONIn the common-emitter configuration , the emitter is common or reference to

both the input and

output terminals (in this case common to both the base and collector

terminals).

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Common Emitter ConfigurationInput Characteristics for a Common-Emitter Amplifier

The following points may be notedfrom this characteristics

1) The characteristics resembles

that of a forward biased diodecurve. This is expected sincethe the base emitter section oftransistor is a diode and it isforward biased.

2) As compared to CBarrangement, IB increases lessrapidly with VBE. Thereforeinput resistance of a CE circuitis higher than that of CB

circuit.

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Output Characteristics for a Common-Emitter Amplifier

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Output Characteristics for a Common-

Emitter Amplifier cont. In the active region of a common-emitter

amplifier the collector-base junction is reverse-biased, while the base-emitter junction is forward-biased.

For linear (least distortion) amplificationpurposes, cutoff for the common emitterConfiguration will be defined by IC =ICEO.

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Common Collector ConfigurationThe collector is common to both input (base - collector) and output(emitter

collector) of the transistor.

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Common Collector Transistor

Characteristics Cut-off region: VCE is at

maximum and IC is atminimum (IC max=ICEO).

Saturation region: IC is atmaximum and VCE is atminimum (VCE max =

VCE sat = VCEO).

Active region: Thetransistor operatesbetween saturation andcutoff.

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Thanks to all of you