Electronic2devices Electron2flow2version Thomas2l.2Floyd Ninth2edition ISBN 10: 1-292-04053-X ISBN 13: 978-1-292-04053-0

Electronic2Devices2:2Electron2Flow2Version22222Floyd222229e Electronic2Devices Electron2Flow2Version Thomas2L.2Floyd Ninth2Edition ISBN 10: 1-292-04053-X ISBN 13: 978-1-292-04053-0

Pearson Education Limited Edinburgh Gate Harlow Essex CM20 2JE England and Associated Companies throughout the world

Visit us on the World Wide Web at: www.pearsoned.co.uk

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without either the prior written permission of the publisher or a licence permitting restricted copying in the United Kingdom issued by the Copyright Licensing Agency Ltd, Saffron House, 6–10 Kirby Street, London EC1N 8TS.

All trademarks used herein are the property of their respective owners. The use of any trademark in this text does not vest in the author or publisher any trademark ownership rights in such trademarks, nor does the use of such trademarks imply any afﬁ liation with or endorsement of this book by such owners.

ISBN 10: 1-292-04053-X ISBN 10: 1-269-37450-8 ISBN 13: 978-1-292-04053-0 ISBN 13: 978-1-269-37450-7

British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library

Printed in the United States of America

Copyright_Pg_7_24.indd 1 7/29/13 11:28 AM TRANSISTOR BIAS CIRCUITS

ANSWERS TO ODD-NUMBERED PROBLEMS

1. Saturation 23. IC = 16.3 mA; VCE =-6.95 V 3. 18 mA 25. 2.53 kÆ

5. VCE = 20 V; IC(sat) = 2 mA 27. 7.87 mA; 2.56 V

7. See Figure ANS–15. 29. ICQ = 92.5 mA; VCEQ = 2.75 V

9. (a) IC(sat) = 50 mA 31. 27.7 mA to 69.2 mA; 6.23 V to 2.08 V; Yes

(b) VCE(CUTOFF) = 10 V 33. V1 = 0 V, V2 = 0 V, V3 = 8 V

(c) IB = 250 mA; IC = 25 mA; VCE = 5 V 35. (a) Open collector (b) No problems (c) Transistor shorted (d) Open emitter collector-to-emitter P = 20 mW ⍀ D(min) 1.2 k 37. (a) 1: 10 V, 2: float, 3: -3.59 V, 4: 10 V 186 k⍀ + (b) 1: 10 V, 2: 4.05 V, 3: 4.75 V, 4: 4.05 V 10 V + – (c) 1: 10 V, 2: 0 V, 3: 0 V, 4: 10 V 10 V – (d) 1: 10 V, 2: 570 mV, 3: 1.27 V, 4: float (e) 1: 10 V, 2: 0 V, 3: 0.7 V, 4: 0 V

ᮡ FIGURE ANS–15 (f) 1: 10 V, 2: 0 V, 3: 3.59 V, 4: 10 V

39. R1 open, R2 shorted, BE junction open 11. 63.2 41. VC = VCC = 9.1 V, VB normal, VE = 0 V 13. I Х 809 mA; V = 13.2 V C CE 43. None are exceeded. 15. See Figure ANS–16. 45. 457 mW

VEE 47. See Figure ANS–17. +9 V

+15 V R RE 2 ⍀ 15 k⍀ 1.0 k RC 2.0 k⍀ R B 2N3904 R1 R ⍀ C Nearest standard values 47 k 2.2 k⍀ 286 k⍀ assuming βDC = 100

ᮡ FIGURE ANS–17 ᮡ FIGURE ANS–16

17. (a)-1.63 mA, -8.16 V (b) 13.3 mW

19. VB =-186 mV; VE =-0.886 V; VC = 3.14 V 21. 0.09 mA

281 TRANSISTOR BIAS CIRCUITS

49. See Figure ANS–18. 51. Yes 53. V will be less, causing the transistor to saturate at a slightly 9 V CEQ higher temperature, thus limiting the low temperature response.

55. RC open R RC 57. R open 1 ⍀ 2 2.0 k⍀ 3.0 k 59. RC shorted 2N3904

R 2 R 620 ⍀ E 1.0 k⍀

ᮡ FIGURE ANS–18

282 BJT AMPLIFIERS

CHAPTER OUTLINE APPLICATION ACTIVITY PREVIEW 1 Amplifier Operation The Application Activity in this chapter involves a preamplifier 2 Transistor AC Models circuit for a public address system. The complete system 3 The Common-Emitter Amplifier includes the preamplifier, a power amplifier, and a dc power supply. You will focus on the preamplifier in this chapter. 4 The Common-Collector Amplifier 5 The Common-Base Amplifier VISIT THE COMPANION WEBSITE 6 Multistage Amplifiers 7 The Differential Amplifier Study aids and Multisim files for this chapter are available at 8 Troubleshooting http://www.pearsonhighered.com/electronics Application Activity GreenTech Application: Wind Power INTRODUCTION The things you learned about biasing a transistor are now CHAPTER OBJECTIVES applied in this chapter where bipolar junction transistor (BJT) circuits are used as small-signal amplifiers. The term ◆ Describe amplifier operation small-signal refers to the use of signals that take up a rela- ◆ Discuss transistor models tively small percentage of an amplifier’s operational range. ◆ Describe and analyze the operation of common-emitter Additionally, you will learn how to reduce an amplifier to an amplifiers equivalent dc and ac circuit for easier analysis, and you will learn about multistage amplifiers. The differential amplifier ◆ Describe and analyze the operation of common-collector is also covered. amplifiers ◆ Describe and analyze the operation of common-base amplifiers ◆ Describe and analyze the operation of multistage amplifiers ◆ Discuss the differential amplifier and its operation ◆ Troubleshoot amplifier circuits

KEY TERMS ◆ r parameter ◆ Emitter-follower ◆ Common-emitter ◆ Common-base ◆ ac ground ◆ Decibel ◆ Input resistance ◆ Differential amplifier ◆ Output resistance ◆ Common mode ◆ Attenuation ◆ CMRR (Common-mode ◆ Bypass capacitor rejection ratio) ◆ Common-collector

283 BJT AMPLIFIERS

1 AMPLIFIER OPERATION The biasing of a transistor is purely a dc operation. The purpose of biasing is to estab- lish a Q-point about which variations in current and voltage can occur in response to an ac input signal. In applications where small signal voltages must be amplified— such as from an antenna or a microphone—variations about the Q-point are relatively small. Amplifiers designed to handle these small ac signals are often referred to as small-signal amplifiers. After completing this section, you should be able to o Describe amplifier operation o Identify ac quantities u Distinguish ac quantities from dc quantities o Discuss the operation of a linear amplifier u Define phase inversion u Graphically illustrate amplifier operation u Analyze ac load line operation

HISTORY NOTE AC Quantities Dc quantities were identified by nonitalic uppercase (capital) subscripts such as I , I , V , The American inventor Lee De C E C and V . Lowercase italic subscripts are used to indicate ac quantities of rms, peak, and Forest (1873–1961) is one of CE peak-to-peak currents and voltages: for example, I , I , I , V , and V (rms values are several pioneers of radio c e b c ce assumed unless otherwise stated). Instantaneous quantities are represented by both lower- development. De Forest case letters and subscripts such as i , i , i , and v . Figure 1 illustrates these quantities for experimented with receiving long- c e b ce a specific voltage waveform. distance radio signals and in 1907 patented an electronic device named the audion, which was the ᮣ FIGURE 1 V first amplifier. De Forest’s new Vce can represent rms, average, peak, three-electrode (triode) vacuum or peak-to-peak, but rms will be tube boosted radio waves as they assumed unless stated otherwise. vce were received and made possible can be any instantaneous value on rms what was then called “wireless avg the curve. Vce telephony,” which allowed the V Vce human voice, music, or any ce

broadcast signal to be heard. VCE Vce

vce

0 t 0

In addition to currents and voltages, resistances often have different values when a circuit is analyzed from an ac viewpoint as opposed to a dc viewpoint. Lowercase subscripts are used to identify ac resistance values. For example, Rc is the ac collector resistance, and RC is the dc collector resistance. You will see the need for this distinction later. Resistance values internal to the transistor use a lowercase r¿ to show it is an ac resistance. An example is the internal ac emitter resistance, re¿.

284 BJT AMPLIFIERS

The Linear Amplifier A linear amplifier provides amplification of a signal without any distortion so that the output signal is an exact amplified replica of the input signal. A voltage-divider biased transistor with a sinusoidal ac source capacitively coupled to the base through C1 and a load capacitively coupled to the collector through C2 is shown in Figure 2. The coupling capacitors block dc and thus prevent the internal source resistance, Rs, and the load resistance, RL, from changing the dc bias voltages at the base and collector. The capacitors ideally ap- pear as shorts to the signal voltage. The sinusoidal source voltage causes the base voltage to vary sinusoidally above and below its dc bias level, VBQ. The resulting variation in base current produces a larger variation in collector current because of the current gain of the transistor.

ᮤ +VCC FIGURE 2

Ic An amplifier with voltage-divider V b ICQ bias driven by an ac voltage source VBQ R 1 RC with an internal resistance, Rs.

Vce C2 VCEQ Rs I C1 b IBQ V s R2 RE RL

As the sinusoidal collector current increases, the collector voltage decreases. The collector current varies above and below its Q-point value, ICQ, in phase with the base current. The sinusoidal collector-to-emitter voltage varies above and below its Q-point value, VCEQ, 180° out of phase with the base voltage, as illustrated in Figure 2. A transistor always produces a phase inversion between the base voltage and the collector voltage. A Graphical Picture The operation just described can be illustrated graphically on the ac load line, as shown in Figure 3. The sinusoidal voltage at the base produces a base current that varies above and below the Q-point on the ac load line, as shown by the arrows.

ᮤ IC FIGURE 3 Graphical ac load line operation of I BQ the amplifier showing the variation Ic(sat) I b of the base current, collector current, and collector-to-emitter voltage Ic about their dc Q-point values. Ib and I Ic are on different scales. CQ Q

ac load line

0 V ce(cutoff ) VCE Vce

VCEQ

285