Bipolar Junction Transistor

The basic principle involved is the use of the voltage between two terminals to control

the current flowing in the third terminal.

1

Reference: Sedra & Smith, “Microelectronic Circuits”, 6th edition.

The active mode is the one used if the transistor is to operate as an amplifier.

Switching applications (e.g., logic circuits) utilize both the cutoff mode and the

saturation mode.

Simplified Structure and Modes of Operation

2

Operation of the npn Transistor in the Active Mode

The Collector Current The Base Current

The Emitter Current

3

4

The pnp Transistor

5

Circuit Symbols and Conventions

6

7

1

2

3

8

9

10

BJT Circuits at DC

HIGHEST

MEDIUM

LOWEST

ACTIVE REGION

11

12

13

14

15

16

17

Dependence of iC on the Collector Voltage—The Early Effect

18

given by

𝒓𝑶 = 𝑽𝑨

𝑰𝑪

𝐼𝐶 = 𝑐𝑜𝑙𝑙𝑒𝑐𝑡𝑜𝑟 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑎𝑡 𝑏𝑖𝑎𝑠 𝑝𝑜𝑖𝑛𝑡 19

𝑉𝐴 = 𝐸𝑎𝑟𝑙𝑦 𝑉𝑜𝑙𝑡𝑎𝑔𝑒

20

21

Applying the BJT in Amplifier Design

22

Biasing the BJT to Obtain Linear Amplification

23

24

Biasing in BJT Amplifier Circuits

The Classical Discrete-Circuit Bias Arrangement

1

25

26

Typically one selects R1 and R2 such that their current is in the range of IE to 0.1IE.

27

28

29

A Two-Power-Supply Version of the Classical Bias Arrangement 2

30

31

Biasing Using a Collector-to-Base Feedback Resistor

32

(6.104)

33

34

Biasing Using a Constant-Current Source

Fig. 6.63

35

36 Fig. 6.63