1. Introduction to BJT Amplifier
Bipolar Junction Transistor (Review)

2. 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

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

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

5. 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?

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

7. 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:

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

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

10. Common-Emitter Circuit
with an npn transistor
with a pnp transistor
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
Usually VBE(on) = 0.7 V
Common-emitter dc equivalent circuit
Look for calculation examples in Neamen (Chapter 5), Example 5.3 & 5.4

17. 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

18. 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

19. 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)

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

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