Introduction to BJT Amplifier Bipolar Junction Transistor (Review)

n-type & p-type semiconductors Si = 14 n-type: - to increase the no. of conduction-band electrons in intrinsic silicon (such as As, P, Bi, Sb) P = 15 - majority carrier: electrons p-type: - to increase the no. of holes in intrinsic silicon (such as B, In, Ga) B = 5 - majority carrier: holes

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

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

BJT Current The emitter current ( iE ) is the sum of the collector current (iC) and the base current (iB) iB << iE and iC OTHER PRAMETERS & EQUATIONS?

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

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

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

Biasing of BJT Remember…! for normal operation AND emitter-base junction is always forward-biased AND collector-base junction is always reverse-biased

Common-Emitter Circuit with an npn transistor with a pnp transistor with a pnp transistor biased with a positive voltage source

DC Analysis: Common-Emitter Circuit Transistor current-voltage characteristics of the common-emitter circuit

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

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

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

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 mA IBQ is the value from the previous slide = 15 µA So, ICQ = βIBQ If β = 200, ICQ = 3000 µA = 3 mA So, VCEQ = 4 V Common- emitter transistor characteristics and the collector-emitter load line

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 Fig 4-20a & b (stacked)

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

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