Output Stages and Power Amplifiers C H A P T E R 11 Output Stages and Power Amplifiers Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.1 Collector current waveforms for transistors operating in (a) class A, (b) class B, (c) class AB, and (d) class C amplifier stages. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.4 Maximum signal waveforms in the class A output stage of Fig. 11.2 under the condition I = VCC /RL or, equivalently, RL = VCC/I. Note that the transistor saturation voltages have been neglected. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.5 A class B output stage. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.6 Transfer characteristic for the class B output stage in Fig. 11.5. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.7 Illustrating how the dead band in the class B transfer characteristic results in crossover distortion. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.8 Power dissipation of the class B output stage versus amplitude of the output sinusoid. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.9 Class B circuit with an op amp connected in a negative-feedback loop to reduce crossover distortion. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.10 Class B output stage operated with a single power supply. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11. 12 Transfer characteristic of the class AB stage in Fig. 11 Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.13 Determining the small-signal output resistance of the class AB circuit of Fig. 11.11. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.15 A class AB output stage utilizing a VBE multiplier for biasing. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.18 An alternative CMOS output stage utilizing a pair of complementary MOSFETs connected in the common-source configuration. The driving circuit is not shown. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.24 Maximum allowable power dissipation versus ambient temperature for a BJT operated in free air. This is known as a “power-derating” curve. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11. 25 The popular TO3 package for power transistors Figure 11.25 The popular TO3 package for power transistors. The case is metal with a diameter of about 2.2 cm; the outside dimension of the “seating plane” is about 4 cm. The seating plane has two holes for screws to bolt it to a heat sink. The collector is electrically connected to the case. Therefore an electrically insulating but thermally conducting spacer is used between the transistor case and the “heat sink.” Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.26 Electrical analog of the thermal conduction process when a heat sink is utilized. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.27 Maximum allowable power dissipation versus transistor-case temperature. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.28 Thermal equivalent circuit for Example 11.8. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.29 Safe operating area (SOA) of a BJT. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.31 The Darlington configuration. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.32 The compound-pnp configuration. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.33 A class AB output stage utilizing a Darlington npn and a compound pnp. Biasing is obtained using a VBE multiplier. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.35 Thermal-shutdown circuit. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.36 The simplified internal circuit of the LM380 IC power amplifier. (Courtesy National Semiconductor Corporation.) Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11. 37 Small-signal analysis of the circuit in Fig. 11. 36 Figure 11.37 Small-signal analysis of the circuit in Fig. 11.36. The circled numbers indicate the order of the analysis steps. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

National Semiconductor Corporation.) Figure 11.38 Power dissipation (PD) versus output power (PL) for the LM380 with RL = 8V. (Courtesy National Semiconductor Corporation.) Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.40 The bridge-amplifier configuration. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.41 Double-diffused vertical MOS transistor (DMOS). Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure 11.44 A class AB amplifier with MOS output transistors and BJT drivers. Resistor R3 is adjusted to provide temperature compensation while R1 is adjusted to yield the desired value of quiescent current in the output transistors. Resistors RG are used to suppress parasitic oscillations at high frequencies. Typically, RG = 100. Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure P11.10 Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure P11.39 Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure P11.41 Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure P11.42 Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure P11.46 Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure P11.52 Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.

Figure P11.54 Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.