Bipolar Junction Transistor Basics BJTs B C E

A transistor consists of two PN junctions A transistor consists of two PN junctions. Thus a transistor is like two PN – junction diodes connected back to back.

The BJT – Bipolar Junction Transistor Note: Normally Emitter layer is heavily doped, Base layer is lightly doped and Collector layer has Moderate doping. The Two Types of BJT Transistors: npn pnp n p n p n p E C E C C C Cross Section Cross Section B B B B Schematic Symbol Schematic Symbol E E

BJT Current Equation n p n p n p IE = IB + IC IE = IB + IC IE IC IE IC - VCE + + VEC - E C E C - - + + VBE VBC IB VEB VCB IB - - + + B B n p n IE = IB + IC p n p IE = IB + IC

Operation of PNP transistor

Operation of NPN transistor Ic C - - - - - - - - - - - - - - - - - n Recombination VCB + _ Electrons + Holes B - - - - - - + - - + - - p + + IB - VBE - _ - - - - - - - - - - - - - - - - - - - - - - - - - - n E IE

Three Possible Configurations of BJT Biasing the transistor refers to applying voltages to the transistor to achieve certain operating conditions. 1. Common-Base Configuration (CB) : input = VEB & IE output = VCB & IC 2. Common-Emitter Configuration (CE): input = VBE & IB output= VCE & IC 3. Common-Collector Configuration (CC) :input = VBC & IB (Also known as Emitter follower) output = VEC & IE

Transistor Circuit Configurations

Common Base Configuration

Common Base Configuration Input Characteristics

Common-Base (CB) Characteristics Vc- Ic (output) Characteristic Curves mA Breakdown Reg. 6 Active Region IE 4 Saturation Region IE=2mA 2 IE=1mA Cutoff IE = 0 VCB 0.8V 2V 4V 6V 8V Early Effect

Common Emitter Configuration

Common Emitter Configuration Input Characteristics

Common Emitter Configuration Output Characteristics BJT’s have three regions of operation: 1) Active - BJT acts like an amplifier (most common use) 2) Saturation - BJT acts like a short circuit 3) Cutoff - BJT acts like an open circuit

Common Emitter Configuration Output Characteristics Region of Operation Description Active Small base current controls a large collector current Saturation VCE(sat) ~ 0.2V, VCE increases with IC Cutoff Achieved by reducing IB to 0, Ideally, IC will also be equal to 0. Active Region IB VCE Saturation Region Cutoff Region IB = 0

Common-Collector Configuration

Common-Collector Input Characteristics

Common-Collector BJT Characteristics Emitter-Current Curves The Common-Collector biasing circuit is basically equivalent to the common-emitter biased circuit except instead of looking at IC as a function of VCE and IB we are looking at IE. Also, since  ~ 1, and  = IC/IE that means IC~IE IE Active Region IB VCE Saturation Region Cutoff Region IB = 0

Comparison

BJT Amplifiers

Single Stage Amplifiers CE Amplifier

CE Amplifier

CE Amplifier

Input & Output Voltages of CE Amplifier

PUZZLE The ages of a father and son add up to 66. The father's age is the son's age reversed. How old could they be?

ANS: Father 51, son 15 Father 42, son 24 Father 60, son 06

PUZZLE Ram sat with his friends in the Chinnaswamy stadium in Bangalore to watch the 100 metres running race organized by the Asian athletics Association. Five rounds were run. After every round half the teams were eliminated. Finally, one team wins the game. How many teams participated in the race?

ANS:32

A grand father has 3 grand children A grand father has 3 grand children. Age difference of two children among them is 3. Eldest child age is 3 times the youngest child’s age and the eldest child age is two year more than the sum of age of other two children. What is the age of the eldest child?

ANS:15

READING

DRAW MINDMAP

SUMMARY

Moulting (Drawing mind map on the board)

Moulting (presentation within the group)