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C H A P T E R 6 Bipolar Junction Transistors (BJTs)

Microelectronic Circuits, Sixth Edition

Figure 6.1

A simplified structure of the

npn

transistor.

Microelectronic Circuits, Sixth Edition

Figure 6.2

A simplified structure of the

pnp

transistor.

Figure 6.3

Current flow in an

npn

transistor biased to operate in the active mode. (Reverse current components due to drift of thermally generated minority carriers are not shown.) Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 6.5

Large-signal equivalent-circuit models of the

npn

BJT operating in the forward active mode.

Microelectronic Circuits, Sixth Edition

Figure 6.6

Circuits for Example 6.1.

Microelectronic Circuits, Sixth Edition

Figure 6.7

Cross-section of an

npn

BJT.

Figure 6.9

Modeling the operation of an

npn

transistor in saturation by augmenting the model of Fig. 6.5(c) with a forward conducting diode

D C

. Note that the current through

D C

increases

i B

and reduces

i C

Figure 6.10

Current flow in a

pnp

transistor biased to operate in the active mode.

Figure 6.11

Two large-signal models for the

pnp

transistor operating in the active mode.

Microelectronic Circuits, Sixth Edition

Figure 6.12

Circuit symbols for BJTs.

Figure 6.13

Voltage polarities and current flow in transistors biased in the active mode.

Microelectronic Circuits, Sixth Edition

Figure 6.14

Circuit for Example 6.2.

Microelectronic Circuits, Sixth Edition

Figure E6.13

Microelectronic Circuits, Sixth Edition

Figure E6.14

Figure 6.18

Large-signal equivalent-circuit models of an

npn

BJT operating in the active mode in the common-emitter configuration with the output resistance

r o

included.

Figure 6.19

Common-emitter characteristics. (

) Basic CE circuit; note that in (

) the horizontal scale is expanded around the origin to show the saturation region in some detail. A much greater expansion of the saturation region is shown in (

Figure 6.20

A simplified equivalent-circuit model of the saturated transistor.

Microelectronic Circuits, Sixth Edition

Figure 6.21

Circuit for Example 6.3.

Table 6.3

Conditions and Models for the Operation of the BJT in Various Modes

(continued)

Figure 6.22

Analysis of the circuit for Example 6.4:

(a)

circuit;

(b)

circuit redrawn to remind the reader of the convention used in this book to show connections to the power supply;

(c)

analysis with the steps numbered.

Figure 6.23

Analysis of the circuit for Example 6.5. Note that the circled numbers indicate the order of the analysis steps.

Figure 6.24

Example 6.6:

(a)

circuit;

(b)

analysis, with the order of the analysis steps indicated by circled numbers.

Figure 6.25

Example 6.7:

(a)

circuit;

(b)

analysis, with the steps indicated by circled numbers.

Figure 6.26

Example 6.8:

(a)

circuit;

(b)

analysis, with the steps indicated by the circled numbers.

Microelectronic Circuits, Sixth Edition

Figure 6.27

Example 6.9:

(a)

circuit;

(b)

analysis with steps numbered.

Microelectronic Circuits, Sixth Edition

Figure 6.28

Circuits for Example 6.10.

Microelectronic Circuits, Sixth Edition

Figure 6.29

Circuits for Example 6.11.

Microelectronic Circuits, Sixth Edition

Figure E6.30

Figure 6.30

Example 6.12:

(a)

circuit;

(b)

analysis with the steps numbered.

Figure 6.32

Biasing the BJT amplifier at a point Q located on the active-mode segment of the VTC.

Figure 6.34

Graphical construction for determining the VTC of the amplifier circuit of Fig. 6.33(a).

Microelectronic Circuits, Sixth Edition

Figure 6.38

Illustrating the definition of

π and

r e

Figure 6.39

The amplifier circuit of Fig. 6.36(a) with the dc sources (

V BE

and

V CC

) eliminated (short-circuited). Thus only the signal components are present. Note that this is a representation of the signal operation of the BJT and not an actual amplifier circuit.

Figure 6.40

Two slightly different versions of the hybrid π model for the small-signal operation of the BJT. The equivalent circuit in

(a)

represents the BJT as a voltage-controlled current source (a transconductance amplifier), and that in

(b)

Microelectronic Circuits, Sixth Edition

Figure 6.43

Signal waveforms in the circuit of Fig. 6.42.

(continued)

Figure 6.44 (a)

circuit;

(b)

dc analysis;

(c)

circuit with the dc sources eliminated;

(d)

Figure 6.45

Input and output waveforms for the circuit of Fig. 6.44. Observe that this amplifier is noninverting, a property of the grounded base configuration.

Figure 6.46

Performing signal analysis directly on the circuit diagram with the BJT small-signal model implicitly employed: (

) Circuit for Example 6.14; (

Figure 6.47

The hybrid  small-signal model, in its two versions, with the resistance

r o

included.

Microelectronic Circuits, Sixth Edition

Figure E6.41

Microelectronic Circuits, Sixth Edition

Table 6.4

Figure 6.48

The three basic configurations of BJT amplifier. The biasing arrangements are not shown.

Figure 6.51

Performing the analysis directly on the circuit with the BJT model used implicitly.

Figure 6.52

The CE amplifier with an emitter resistance

R e

;

(a)

Circuit without bias details;

(b)

Figure 6.53

(

) CB amplifier with bias details omitted; (

) Amplifier equivalent circuit with the BJT represented by its T Model.

Microelectronic Circuits, Sixth Edition

Figure 6.54

Illustrating the need for a unity-gain buffer amplifier.

Microelectronic Circuits, Sixth Edition

Figure 6.58

Circuit for Example 6.19.

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C H A P T E R 6 Bipolar Junction Transistors (BJTs)

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