CHAPTER 6
Bipolar Junction Transistors (BJTs)
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Figure 6.1 A simplified structure of the npn transistor.
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Figure 6.2 A simplified structure of the pnp transistor.
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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.)
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Figure 6.5 Large-signal equivalent-circuit models of the npn BJT operating in the forward active mode.
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Figure 6.6 Circuits for Example 6.1.
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Figure 6.7 Cross-section of an npn BJT.
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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 DC.
Note that the current through DC increases iB and reduces iC.
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Figure 6.10 Current flow in a pnp transistor biased to operate in the active mode.
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Figure 6.11 Two large-signal models for the pnp transistor operating in the active mode.
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Figure 6.12 Circuit symbols for BJTs.
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Figure 6.13 Voltage polarities and current flow in transistors biased in the active mode.
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Figure 6.14 Circuit for Example 6.2.
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Figure E6.13
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Figure E6.14
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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 ro included.
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Figure 6.19 Common-emitter characteristics. (a) Basic CE circuit; note that in (b) 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 (c).
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Figure 6.20 A simplified equivalent-circuit model of the saturated transistor.
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Figure 6.21 Circuit for Example 6.3.
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Table 6.3 Conditions and Models for the Operation of the BJT in Various Modes (continued)
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Table 6.3 (continued)
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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.
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Figure 6.23 Analysis of the circuit for Example 6.5. Note that the circled numbers indicate the order of the analysis steps.
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Figure 6.24 Example 6.6: (a) circuit; (b) analysis, with the order of the analysis steps indicated by circled numbers.
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Figure 6.25 Example 6.7: (a) circuit; (b) analysis, with the steps indicated by circled numbers.
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Figure 6.26 Example 6.8: (a) circuit; (b) analysis, with the steps indicated by the circled numbers.
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Figure 6.27 Example 6.9: (a) circuit; (b) analysis with steps numbered.
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Figure 6.28 Circuits for Example 6.10.
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Figure 6.29 Circuits for Example 6.11.
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Figure E6.30
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Figure 6.30 Example 6.12: (a) circuit; (b) analysis with the steps numbered.
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Figure 6.32 Biasing the BJT amplifier at a point Q located on the active-mode segment of the VTC.
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Figure 6.34 Graphical construction for determining the VTC of the amplifier circuit of Fig. 6.33(a).
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Figure 6.38 Illustrating the definition of rπ and re.
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Figure 6.39 The amplifier circuit of Fig. 6.36(a) with the dc sources (VBE and VCC) 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.
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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) represents the BJT as a currentcontrolled current source (a current amplifier).
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Figure 6.43 Signal waveforms in the circuit of Fig. 6.42. (continued)
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Figure 6.43 (continued)
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Figure 6.44 (a) circuit; (b) dc analysis; (c) circuit with the dc sources eliminated; (d) small-signal analysis using the T model for the BJT.
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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.
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Figure 6.46 Performing signal analysis directly on the circuit diagram with the BJT small-signal model implicitly employed:
(a) Circuit for Example 6.14; (b) Circuit for Example 6.16.
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Figure 6.47 The hybrid- small-signal model, in its two versions, with the resistance ro included.
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Figure E6.41
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Table 6.4 Small-Signal Models of the BJT
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Figure 6.48 The three basic configurations of BJT amplifier. The biasing arrangements are not shown.
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Figure 6.51 Performing the analysis directly on the circuit with the BJT model used implicitly.
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Figure 6.52 The CE amplifier with an emitter resistance Re; (a) Circuit without bias details;
(b) Equivalent circuit with the BJT replaced with its T model.
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Figure 6.53 (a) CB amplifier with bias details omitted; (b) Amplifier equivalent circuit with the BJT represented by its T Model.
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Figure 6.54 Illustrating the need for a unity-gain buffer amplifier.
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Figure 6.58 Circuit for Example 6.19.
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