Small Signal Audio Design
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Small Signal Audio Design Douglas Self AMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK OXFORD PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO Focal Press is an imprint of Elsevier Focal Press is an imprint of Elsevier The Boulevard, Langford Lane, Kidlington, Oxford, OX5 1GB, UK 30 Corporate Drive, Suite 400, Burlington, MA 01803, USA First published 2010 Copyright ª 2010 Douglas Self. Published by Elsevier Ltd. All rights reserved. The right of Douglas Self to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988 No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangement with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. British Library Cataloguing in Publication Data Self, Douglas. Small signal audio design. 1. Acoustical engineering. 2. Signal processing. I. Title 620.2-dc22 Library of Congress Number: 2009939461 ISBN: 978-0-240-52177-0 For information on all Focal Press publications visit our website at www.focalpress.com Printed and bound in the United Kingdom 07 08 09 10 11 11 10 9 8 7 6 5 4 3 2 1 Contents Preface ...................................................................................................................... xiii About the Author ..................................................................................................... xvii Acronyms ................................................................................................................ xviii Chapter 1 The Basics ....................................................................................................... 1 Signals .................................................................................................................................1 Amplifiers ............................................................................................................................2 Voltage Amplifiers............................................................................................................2 Transconductance Amplifiers ............................................................................................2 Current Amplifiers............................................................................................................3 Transimpedance Amplifiers...............................................................................................3 Negative Feedback................................................................................................................4 Nominal Signal Levels..........................................................................................................5 Gain Structures.....................................................................................................................6 Amplification Then Attenuation ........................................................................................6 Attenuation Then Amplification ........................................................................................7 Raising the Input Signal to the Nominal Level...................................................................7 Active Gain Controls........................................................................................................8 Noise ...................................................................................................................................8 Johnson Noise ......................................................................................................................9 Shot Noise .........................................................................................................................11 1/f Noise (Flicker Noise).....................................................................................................12 Popcorn Noise ....................................................................................................................13 Summing Noise Sources .....................................................................................................13 Noise in Amplifiers.............................................................................................................14 Noise in Bipolar Transistors ................................................................................................16 Bipolar Transistor Voltage Noise.....................................................................................16 Bipolar Transistor Current Noise.....................................................................................17 Noise in JFETs...................................................................................................................20 Noise in Op-Amps..............................................................................................................21 Low-Noise Op-Amp Circuitry .............................................................................................22 Noise Measurements...........................................................................................................23 How to Attenuate Quietly ...................................................................................................23 iii iv Contents How to Amplify Quietly .....................................................................................................25 How to Invert Quietly .........................................................................................................26 How to Balance Quietly......................................................................................................28 Ultra-Low-Noise Design with Multipath Amplifiers .............................................................28 Ultra-Low-Noise Voltage Buffers ....................................................................................29 Ultra-Low-Noise Amplifiers............................................................................................30 References .........................................................................................................................32 Chapter 2 Components ................................................................................................... 33 Conductors.........................................................................................................................33 Copper and Other Conductive Elements ..........................................................................34 The Metallurgy of Copper ..............................................................................................35 Gold and Its Uses...........................................................................................................35 Cable and Wiring Resistance ..........................................................................................36 PCB Track Resistance ....................................................................................................37 PCB Track-to-Track Crosstalk.............................................................................................39 Impedances and Crosstalk: A Case History ..........................................................................40 Resistors ............................................................................................................................42 Through-Hole Resistors ..................................................................................................43 Surface-Mount Resistors.................................................................................................43 Resistor Imperfections ....................................................................................................45 Resistor Noise................................................................................................................46 Resistor Non-Linearity ...................................................................................................48 Capacitors ..........................................................................................................................51 Capacitor Non-Linearity Examined