Introduction to BJT Amplifier Bipolar Junction Transistor Review

Introduction to BJT Amplifier Bipolar Junction Transistor (Review) 1

n-type & p-type semiconductors n n n-type: - to increase the no. of conduction-band electrons in intrinsic silicon (such as As, P, Bi, Sb) - majority carrier: electrons p-type: - to increase the no. of holes in intrinsic silicon (such as B, In, Ga) - majority carrier: holes 2

What is pn junction? Still remember this? What’s the different between these two figures? Which one is forward-biased and reverse-biased? 3

Remember these symbols? Still remember about BJT? Which one is NPN, PNP? What is C, B, E…? 4

BJT Current The emitter current ( i. E ) is the sum of the collector current (i. C) and the base current (i. B) i. B << i. E and i. C OTHER PRAMETERS & EQUATIONS? 5

BJT n Basic structure and schematic symbol approximate equivalents transistor symbols npn type pnp type 6

Refresh… n Common-emitter current gain, β n n Common-base current gain, α n n Range: 50 < β < 300 Range: always slightly less than 1 The current relationship between these 2 parameters are as follows: 7

Refresh. . . n BJT as amplifying device n B-E junction is forward-biased n B-C junction is reverse-biased 8

Biasing of BJT n Remember…! for normal operation Ä emitter-base junction is always forwardbiased AND Ä collector-base junction is always reversebiased 9

Common-Emitter Circuit (a) with an npn transistor (b) with a pnp transistor (c) with a pnp transistor biased with a positive voltage source 10

DC Analysis: Common-Emitter Circuit Transistor current-voltage characteristics of the commonemitter circuit 11

DC Analysis: Common-Emitter Circuit Common-emitter circuit with an npn transistor Common-emitter dc equivalent circuit, with piecewise linear parameters 12

DC Analysis: Common-Emitter Circuit Usually VBE(on) = 0. 7 V Common-emitter dc equivalent circuit Look for calculation examples in Neamen (Chapter 5), Example 5. 3 & 5. 4 13

DC Analysis: Load Line & Modes of Operation Figure A Base on Figure A, using KVL around B-E loop: Base-emitter junction characteristics and the input load line 14

DC Analysis: Load Line & Modes of Operation Base on Figure A, 2 end points of the load line are found by setting IC = 0 So, VCE = VCC = 10 V When VCE = 0, IC = VCC/RC = 5 m. A IBQ is the value from the previous slide = 15 µA So, ICQ = βIBQ If β = 200, ICQ = 3000 µA = 3 m. A Common- emitter transistor characteristics and the collector-emitter load line So, VCEQ = 4 V 15

BJT as an Amplifier • Amplification of a small ac voltage by placing the ac signal source in the base circuit • Vin is superimposed on the DC bias voltage VBB by connecting them in series with base resistor RB: • Small changes in the base current circuit causes large changes in collector current circuit 16

BJT as an Amplifier (cont’) (a)A bipolar inverter circuit to be used as a time-varying amplifier (b) The voltage transfer characteristic 17

Self- Reading Textbook: Donald A. Neamen, ‘MICROELECTRONICS Circuit Analysis & Design’, 3 rd Edition’, Mc. Graw Hill International Edition, 2007 Chapter 5: The Bipolar Junction Transistor Page: 287 -296, 303 -309. 18