Newnes Guide to Television and Video Technology Newnes Guide to Television and Video Technology Third edition Eugene Trundle, TMIEEIE, MRTS, MISTC OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI Newnes An imprint of Butterworth-Heinemann Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-2041 A division of Reed Educational and Professional Publishing Ltd A member of the Reed Elsevier plc group First published 1988 Second edition 1996 Third edition 2001 # Eugene Trundle 1988, 1996, 2001 All rightsreserved.No part of thispublication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1P 9HE. Applications for the copyright holder's written permission to reproduce any part of thispublication shouldbe addressed to the publishers. British Library Cataloguing in Publication Data A catalogue record for thisbook isavailable from the BritishLibrary. ISBN 0 7506 48104 Typset by Keyword Typesetting Services Ltd, Wallington, Surrey Printed and bound in Great Britain by MPG BooksLtd, Bodmin, Cornwall Contents Preface to third edition vii 1 Basic television 1 2 Light and colour 15 3 Reading and writing in three colours21 4 The PAL system 43 5 Transmission and reception 51 6 Colour decoding 61 7 TV display systems 78 8 The TV receiver 102 9 Teletext 122 10 PAL-Plus, MAC and enhanced TV 132 11 TV sound systems 144 12 Digital TV 165 13 Satellite TV 194 14 Cable TV 215 15 Development of video tape recording 223 16 Magnetic tape basics and video signals 228 17 Video tape: tracksand transport 239 18 Signal processing: video 263 19 Signal processing: audio 294 20 Servo systems and motor drive 308 21 System control for VCRs 324 22 The complete VCR 337 23 Analogue camcordersand home video 345 24 Digital tape formatsand computer editing 359 25 Tape formatscompared 382 26 DVD players391 27 Care, operation and maintenance 399 28 Interconnection and compatibility 406 Index 417 v Preface to third edition The termsof reference for thisbook are very wide, and increasewith each new edition. TV and video take an ever larger part in our leisure, educational and recre- ational activities; here the technology behind them is explored and explained. Much use is made throughout the book of block diagrams. Since integrated circuits ± silicon chips ± have become so widespread, much service data are now presented in block diagram form. To explain principles and techniques I have sometimes used earlier discrete circuits and systems, in which the separate func- tionsand circuit elementscan be clearly discerned. Asthisisbeing written the world of TV and video isin transitionfrom analogue to digital operation in the realms of broadcast/reception, tape recording and disc systems, while a convergence of computer and TV/video technologies is under way. Thisisreflected in thisnew edition of the book, which isaimed at interested laypeople, students, technicians and those in allied fields seeking an insight into TV and VCR practice. I have assumed that the reader has a basic knowledge of electronicsand mechanics.For further reading I can recommend my Television and Video Engineer's Pocket Book; and for those whose interest lies in fault- diagnosis and repair, my Servicing TV, Satellite and Video Equipment, both published by Newnes. My thanksare due once more to my patient and loving wife Anne, whosemoral support, coffee-brewing and keying-in services have kept me going through the three editionsof thisbook. Eugene Trundle vii 1 Basic television For a reasonable understanding of colour television, it is essential that the basic principles of monochrome TV are known. As we shall see, all colour systems are firmly based on the original `electronic-image dissection' idea which goes back to EMI in the 1930s, and is merely an extension (albeit an elaborate one) of that system. Although there are few black and white TVs or systems now left in use, the compatible colour TV system used today by all terrestrial transmitters grew out of the earlier monochrome formats. In the early days it was essential that existing receivers showed a good black and white picture from the new colour transmis- sions, and the scanning standards, luminance signal, and modulation system are the same. What follows is a brief recap of basic television as a building block of the colour TV system to be described in later chapters. Image analysis Because a picture has two dimensions it is only possible to transmit all the infor- mation contained within it in serial form, if we are to use but one wire or RF channel to carry the signal. This implies a dissection process, and requires a timing element to define the rate of analysis; this timing element must be present at both sending and receiving ends so that the analysis of the image at the sending end, and the simultaneous build-up of the picture at the receiver, occur in syn- chronism. Thus a television picture may be dissected in any manner, provided that the receiver assembles its picture in precisely the same way; but the path link between sender and viewer must contain two distinct information streams: video signal, which is an electrical analogy of the light pattern being sent, and timing signals, or synchronisation pulses, to define the steps in the dissection process. The presence of a timing element suggests that each picture will take a certain period to be built up; how long will depend on how quickly we can serialise the picture elements, and this in turn depends on the bandwidth available in the transmission system ± more of this later. 1 Figure 1.1 The scanning process. Horizontal lines are drawn from left to right of the screen by horizontal direction, and `stacked' vertically by the slower- moving vertical deflection field Scanning If we focus the image to be televised on a light-sensitive surface we are ready for the next stage in the dissection process ± the division of the pattern into picture elements or pixels. Each pixel is rather like the individual dots that go to make up a newspaper photograph in that each can only convey one level of shading. Thus the detail, or definition, in the reproduced picture is proportional to the number of pixels. In 625-line television we have approximately 450 000 pixels, adequate for a 67 cm-diagonal picture, but barely sufficient for much larger screens. These individual pixels are arranged in horizontal lines; there are 625 lines in the British TV system. Figure 1.1 shows how the image is scanned, line by line, to read out in serial form the pattern of light and shade which forms the picture. When half the lines have been traced out the scanning spot has reached the bottom of the picture and traced one field. It now flies back to the top of the screen to trace out the rest of the 625 lines in the spaces between those of its first descent. This is known as interlacing, and confers the advantages of a 50 Hz (Hz, Hertz, one cycle per second) flicker rate with the lower scanning speed and lesser bandwidth require- ment of a 25 Hz frame rate. All TV systems use this 2:1 interlaced field technique; its success depends only on accurate triggering of the field scan. Image sensor In earlier designs of TV camera the image pick-up device was a thermionic tube whose light-sensitive faceplate was scanned by a sharply focused electron beam. Currently a solid-state device is used, as shown in Figure 1.2. Its faceplate is made up of an array of hundreds of thousands of silicon photodiodes mounted on a chip, typically 7 mm diagonal, arranged in lines and columns. Though a real sensor of this type may contain 750 diodes per line and 575 rows, our diagram shows a 12 Â 9 matrix for simplicity. During the active field period each reversed- biased diode acts as a capacitor, and acquires an electrical charge proportional to the amount of light falling on it: the televised image is sharply focused on the sensor faceplate by an optical lens system. Each diode is addressed in turn by the sensor's drive circuit so that (as viewed from the front) the charges on the top line of photodiodes are read out first, from left to right. Each line is read out in turn, 2 Figure 1.2 Matrix of silicon photodiodes in an image pick-up chip progressing downwards, until the end of the bottom line is reached after 20 ms (ms, millisecond, 0.001 second). This first vertical scan involves every other line in the diode matrix, nos 1, 3, 5 and so on. Now another scan begins, this time addressing in turn all the photodiodes in lines 2, 4, 6 etc, and that is completed in a further 20 ms. At this point the entire picture has been scanned in two con- secutive sweeps taking a total of 40 ms and simulating the pattern and sequence of Figure 1.1. Charge coupling The capacitors formed by the silicon photodiodes are represented by C1, C2, C3 and C4 in Figure 1.3, which portrays the first four pixels in one television line. C1 acquires a charge proportional to the light level on the first pixel; it appears as a voltage at the output of the first amplifier A1.