Manager, Monolithic Engineering
`Burr-Brown Research Corporation
`
`Amplifier Product Marketing Engineer
`Burr-Brown Research Corporation
`
`Micro Motion 1033
`
`OPERATIONAL
`
`AMPLIFIERS
`DeSign and Applications
`
`JERALD G. GRAEME
`Editor, Part 1
`
`GENE E. TOBEY
`Editor, Part 2
`
`LAWRENCE P. HUELSMAN, Ph.D.
`Consulting Editor
`
`Professor of Electrical Engineering
`The University of Arizona
`
`McGRAW-HILL BOOK COMPANY
`
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`mmkmmAAfl.
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`-ANJLEW44
`
`A
`
`no)-
`
`1
`
`Micro Motion 1033
`
`

`

`Copyright © 1971 by Burr-Brown Research Corporation. All Rights
`Reserved. Printed in the United States of America. No part of this
`publication may be reproduced, stored in a retrieval system, or trans-
`mitted, in any form or by any means, electronic, mechanical, photo-
`copying, recording, or otherwise, Without the prior Written permission
`of the publisher. Library of Congress Catalog Card Number 74-163297
`
`The information conveyed in this book has been carefully reviewed
`and believed to be accurate and reliable; however, no responsibility
`is assumed for the operability of any circuit diagram or inaccuracies
`in calculations or statements. Further, nothing herein conveys to
`the purchaser a license under the patent rights of any individual or
`organization relating to the subject matter described herein.
`
`ISBN 07-064917-0
`
`890 KPKP 7987654
`
` OPERATIONAL AMPLIFIERS
`
`
`
`1A
`
`t,
`
`
`
`
`CO N'I
`
`Contributor
`
`Preface
`Historical I
`
`Part:
`
`1. DIFFEREI
`
`1.1
`Lox
`1.2
`Hig
`1.3
`CO]
`1.4 Dii
`1.5 Dif
`
`2.
`
`INPUT E
`
`2.1
`2.2
`2.3
`2.4
`
`In}:
`In}:
`In}:
`Eqi
`
`
`
`2
`
`

`

`LICATION
`
`Waveform Generators
`
`381
`
`; rating of
`
`rcuit
`
`for
`
`ad to as _a
`ave quite
`r triangle
`ut circuit
`es should
`de of the
`
`res act as
`1 current
`ge wave-
`lhown in
`
`ig. 10.10
`
`ZzE
`Eo=_ o
`
`B
`
`
`
`
`
`Fig. 10.11 Triangle generator waveforms.
`
`would be R2 = 10 k9, R1 = 5 k9, R3 = 100 k9, 01 = 0.1 ”F. These
`values will provide a triangle wave of approximately +7.2 to —7.2 V
`swing at a frequency of 500 Hz.
`
`10.3
`
`Sine-wave Generators3’5
`
`One of the most important waveforms that an engineer may be called
`upon to generate is the sinusoidal waveform.
`In this section We shall
`treat a variety of techniques which may be used to perform this task.
`Specifically we shall investigate the use of Wien—bridge oscillators, quad-
`rature oscillators, and phase-shift oscillators. For the Wien-bridge and
`the quadrature oscillator case several different circuits are considered.
`These may be applied to different special requirements as indicated in ,
`the discussion of the circuits.
`
`A Wien bridge
`10.3.1 Wien-bridge oscillator—general description
`may be combined with an operational amplifier to form an excellent sine-
`wave generator. Some sort of automatic gain control is generally used
`to stabilize the magnitude of the output sinusoid. A general schematic
`of a Wien-bridge oscillator is shown in Fig. 10.12. To see how this circuit
`operates let us assume that the output eo is a sinusoid; then the feedback
`ratio of the bridge is given by
`
`2.
`
`R2
`
`2. + z. “ R. + R2<1 + 02/0.) + j(wR.R202 — l/wc.)
`
`where Z1 = R1 + l/ij1 and Z2 = R2/(1 + ij2C2). The operational
`amplifier Will maintain 0 V between its input terminals; thus,
`
`Z1+Z2_
`
`3
`
`

`

`382
`
`IW~N BRiDGE­
`I
`I
`
`-,
`I
`
`APPLICATIO.N
`
`--,
`I
`I
`
`I
`
`J
`
`AMPLITUDE
`DElECTOR
`
`AMPLITUDE
`REFERENCE
`
`1...
`
`GAIN CONTR OL CIRCUIT
`
`Fig. 10.12 Wien-bridge oscillator.
`
`where :Ito is a phasor representing the voltage eo(t). The condition for
`oscillation is
`
`1
`Wo = ---:;====
`VR 1R 2C1C2
`If we make Rl = R2 and C l = C 2, then
`1
`1
`/3=-
`Wo = R1C l
`3
`If /3 = H and the condition of Rl = R2 and C l = C 2 is met, then the
`output will be a sinusoid of frequency 1/ 27rRC.
`It should be noted that, so long as /3 is H, the circuit will oscillate at any
`amplitude. Also, if /3 is less than 7~, the oscillation will diverge and if /3
`is more than 73 the oscillation will converge. Thus it is common practice
`to provide some sort of automatic amplitude control. This is usually
`
`and
`
`Waveform Ge
`
`done by va
`Incandesce
`multipliers
`
`10.3.2 Pre
`of the genl
`sider the c
`by R l , Cl
`plified by}
`Aa and A4•
`only when
`A diode br
`can be use
`The int
`
`l tradeoff b
`allow the (
`any distu
`minimize
`ously, will
`
`where Rl
`10 kHz ar
`and excell
`operate at
`must be c
`Althoul
`are used, ~
`In such I
`used to III
`
`·10.3.3 L(
`circuit pr
`requiring
`Wien-bri(
`given.
`']
`are requi
`cussed W
`will be il
`impedan<
`diodes, W
`be used v
`
`4
`
`

`

`.ICATION
`
`
`
`ition for
`
`hen the
`
`5 at any
`and if [3
`)ractice
`
`usually
`
`
`
`Waveform Generators
`
`383
`
`done by varying the negative feedback gain (,8) to stabilize the oscillator.
`Incandescent lamps, thermistors, FETs, diode bridges, or general-purpose
`multipliers can all be used for such gain control purposes.
`
`As a typical implementation
`10.3.2 Precise Wien-bridge oscillator4v5
`of the general Wien-bridge oscillator diagram shown in Fig. 10.12, con-
`sider the circuit shown in Fig. 10.13. The actual Wien bridge is formed
`by R1, Cl, R2, and Cg. The oscillatory output of amplifier A1 is am-
`plified by A2, and the output level is sensed bythe absolute-value circuit of
`A3 and A4. The amplifier A4 acts as an error integrator and will stabilize
`only when the absolute value of the input equals the reference amplitude.
`A diode bridge is used for varying the negative feedback of A1. An FET
`can be used for gain control ratherthan the diode bridge if desired.
`The integrator gain is set by capacitor Cg. The choice of C3 is a
`tradeoff between response time and distortion. Small values of C3 will
`allow the circuit to reach its stable value very rapidly. Also, response to
`any disturbance is rapid. On the other hand, making C3 large will
`minimize distortion. The frequency of oscillation, as discussed previ-
`ously, will be
`
`be used with either a fixed load at eo or a buffer must be added. As with
`
`f;
`
`
`1
`
`= 21rR101
`
`where R1 = R2 and C1 = C2. Frequencies in the range of 10 Hz to
`10 kHz are practical for this circuit. Distortion of less than 0.1 percent
`and excellent frequency stability are readily achieved. The circuit will
`operate at frequencies above 10 kHz, but the type of operational amplifier
`must be carefully chosen and stray capacitances should be considered.
`Although, in the circuit shown in Fig. 10.13, five operational amplifiers
`are used, similar circuits are available in miniature encapsulated packages.
`In such packages,
`integrated—circuit operational amplifiers are usually
`used to minimize the size.
`‘
`
`The Wien—bridge oscillator
`10.3.3 Low-cost Wien-bridge oscillator
`circuit presented in the preceding paragraphs has the disadvantage of
`requiring five operational amplifiers. In Fig. 10.14 a circuit diagram for a
`Wien-bridge oscillator which requires only one operational amplifier is
`given. The primary virtue of this circuit is that very few components
`are required. Distortion will be greater than with the previously dis-
`cussed Wien bridge. But, depending upon care of adjustment, distortion
`will be in the range of 1 to 5 percent. This circuit has high output
`impedance, and any loading at eo will shift the operating point of the
`diodes, which will in turn change the amplitude. Thus this circuit must
`
`5
`
`