1. Introduction to BJT Amplifier BJT (Review)

2. Still remember about BJT? 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?

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

4. Refresh.. Common-emitter current gain, β 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:

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

6. BIASING OF BJT Remember…! for normal operation  emitter-base junction is always forward- biased AND  collector-base junction is always reverse- biased

7. FORWARD BIASING E/B JUNCTION

8. REVERSE BIASING C/B JUNCTION

9. BIASING NPN TRANSISTOR

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

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

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

13. DC Analysis - Common-Emitter Circuit Look for calculation examples in Neamen (Chapter 3), Example 3.3 & 3.4 Usually V BE (on) = 0.7 V Common-emitter dc equivalent circuit

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

15. Base on Figure A, 2 end points of the load line are found by setting I C = 0 So, V CE = V CC = 10 V When V CE = 0, I C = V CC /R C = 5 mA I BQ is the value from the previous slide = 15 µA So, I CQ = βI BQ If β = 200, I CQ = 3000 µA = 3 mA So, V EQ = 4 V DC Analysis - Load Line & Modes of Operation Common- emitter transistor characteristics and the collector-emitter load line

16. BJT as an Amplifier Amplification of a small ac voltage by placing the ac signal source in the base circuit V in is superimposed on the DC bias voltage V BB by connecting them in series with base resistor R B : Small changes in the base current circuit causes large changes in collector current circuit END