ANALOG CMOS FILTERS FOR VERY HIGH FREQUENCIES

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1 ANALOG CMOS FILTERS FOR VERY HIGH FREQUENCIES

2 THE KLUWER INTERNATIONAL SERIES IN ENGINEERING AND COMPUTER SCIENCE ANALOG CIRCUITS AND SIGNAL PROCESSING Consulting Editor Mohammed Ismail Ohio State University

3 ANALOG CMOS FILTERS FOR VERY HIGH FREQUENCIES by Bram Nauta Philips Research Laboratories ~. " SPRINGER SCIENCE+BUSINESS MEDIA, LLC

4 Library ofcongress Cataloging-in-Publication Data Nauta, Bram, Analog CMOS filters for very high frequencies / by Bram Nauta. p. cm. -- (The K1uwer international series in engineering and computer science. Analog circuits and signal processing) Includes bibliographieal references and index. ISBN ISBN (ebook) DOI / Electric filters--design and construction. 2. Metal oxide semiconductors, Complementary. 3. Integrated circuits. 1. Title. II. Series. TK7872.F5N I 324--dc CIP Copyright 1993 by Springer Science+Business Media New York Originally published by Kluwer Academic Publishers, New York in 1993 Softcover reprint ofthe hardcover 1st edition 1993 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmi tted in any form or by any means, mechanical, photo-copying, recording, or otherwise, without the prior written permission of the publisher, Springer Science+ Business Media, LLC. Printed on acid-free paper.

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6 CONTENTS PREFACE xi 1 INTRODUCTION 1.1 Introduction 1.2 Active monolithic filters, an overview 1.3 Monolithic analog continuous-time filters 1.4 Research topics FILTER SYNTHESIS FOR (VERY) HIGH FREQUENCIES 2.1 Introduction 2.2 Restrictions for very high frequencies 2.3 Synthesis methods Cascaded biquad synthesis Biquads Example Conclusions Signal flow graph synthesis Introduction Example Conclusions State-space synthesis State-space synthesis Example Conclusions Gyrator synthesis Gyrators Gyrator filter synthesis Examples Conclusions Coupled resonator bandpass filters Design technique Examples

7 viii Contents Conclusions Comparison of synthesis methods 2.4 Sensitivity Sensitivity of LC-Iadder filters Sensitivity of gyrator filters Sensitivity of other filters 2.5 Frequency and impedance level scaling 2.6 Conclusions EFFECT OF NON-IDEALITIES Introduction Effect of finite integrator quality factor Integrator model Effect of finite integrator quality factor Gyrators Canceling of effects of overlap capacitances in a balanced gyrator Dynamic range Noise Distortion Noise and distortion gives dynamic range Dissipation and chip area Capacitors Conclusions 83 4 TRANSCONDUCTOR DESIGN The MOS Transistor Linear MOS transconductors, an overview Design strategy for VHF transconductor VHF transconductor, basic operation V-I conversion Common-mode control and DC-gain enhancement Conclusions Detailed analysis and measurements Output conductance Transconductor bandwidth 105

8 Contents ix Series resistances in capacitors Transconductor-C integrator quality factor Noise Distortion Nonlinearities in V-I conversion Nonlinearities in output conductance Dynamic range Dissipation Parasitic capacitors 4.6 Conclusions TUNING 5.1 Introduction 5.2 The VCO tuning loop 5.3 Quality factor tuning Basic principle Implementation Experimental results 5.4 Supply voltage unit Introduction Basic principle Implementations 5.5 Conclusions FILTER REALIZATIONS 6.1 Introduction 6.2 Third-order elliptic filters Filter design Experimental setup Experimental results Conclusions, third-order elliptic filters 6.3 TV IF Filter Introduction TV front-end Filter specification

9 x Contents IF filter design Experimental results Conclusions, TV IF filter CONCLUSIONS 7.1 Introduction 7.2 Summary 7.3 Original contributions to the thesis 7.4 Recommendations for further research REFERENCES 219 SUBJECT INDEX 229

10 PREFACE This book deals with the design of fully integrated analog CMOS filters for very high frequencies. It describes various synthesis methods and electronic circuit designs suitable for filters with cut-off frequencies ranging from the low megahertz range to several hundreds of megahertz. The book is intended for engineers in research or development and advanced level students. Today IC technology is widely used for fully integration of electronic systems. These systems are in general for a large part realized using digital techniques implemented in CMOS technology. The low power dissipation, high packing density, high noise immunity, ease of design and the relative ease of scaling are the driving forces of CMOS technology for digital applications. Parts of these systems cannot be implemented in the digital domain and will remain analog. In order to achieve complete system integration these analog functions are preferably integrated in the same CMOS technology. An important class of analog circuits that need to be integrated in CMOS are analog filters. This book deals with very high frequency (VHF) filters, which are filters with cut-off frequencies ranging from the low megahertz range to several hundreds of megahertz. Up till recently the maximal cut-off frequencies of CMOS filters were limited to the low megahertz range. By applying the techniques presented in this book the limit could be pushed into the true VHF domain, and integrated VHF filters became feasible. Application of these VHF filters can be found in the field of communication, instrumentation and control systems. For example pre and post filtering for high-speed AD and DA converters, signal reconstruction, signal decoding, etc. The general design philosophy used in this book is, to allow only the absolute minimum of signal carrying nodes throughout the whole filter. This strategy starts at the filter synthesis level and is extended to the level of electronic circuitry. The result is a filter realization in which all capacitors (including parasitics) have a desired function. The advantage of this technique is that high-frequency parasitic effects (parasitic poles/zeros) are minimally present. The first part of the book (chapters 1-3) is on general design for VHF filters, including synthesis methods and analysis of the effects of various non-idealities. The second part (chapters 4-6) describes more specific electronic circuitry suitable for implementing these VHF filters in CMOS technology. This part also includes the experimental results of several demonstration filters. An outline of each chapter is

11 xii Preface given below. Chapter 1 gives an introduction to continuous-time integrated filters, including an historical overview. In chapter 2 various synthesis methods for VHF, such as cascaded biquad, signal flow graph, state-space, gyrator and couple resonator synthesis, are described. All methods use transconductors and capacitors as building blocks and result in filter topologies with on every node a desired capacitance. The methods are compared with respect to sensitivity and scaling properties. In chapter 3 the effects of non-idealities in the transconductor realizations on filter performance is discussed. These effects are illustrated with calculations carried out on a second order bandpass filter. Effects considered are: finite integrator quality factor, noise, distortion, dynamic range, dissipation and chip area. Several compact analytical expressions are derived giving insight in these effects. Chapter 4 deals with transconductor design. A transconductor is presented that has high linearity, and a very large bandwidth (10GHz in 3tLm CMOS) thanks to the absence of internal nodes. The parasitic output resistance of the transconductor is compensated and thus a useful building block for VHF filters is obtained. A detailed analysis of the transconductor is given, including non-quasi-static transistor operation. A link is made with parameters derived in chapter 3. Chapter 5 deals with automatic frequency and quality factor tuning. A special quality factor tuning circuit without signal carrying nodes is presented and analyzed. Furthermore a method is presented for making a wide-band, low-ohmic supply voltage regulation. This regulation is required to tune the cut-off frequency and quality factors of the filters built with the transconductors of chapter 4. In chapter 6 experimental results of 5 demonstration filters designed in 3tLm CMOS are given. These filters are: four third-order elliptic filters with cut-off frequencies ranging from O.5MHz to 100MHz, and one 22-nd order TV-IF filter with 36MHz center frequency. In chapter 7 finally a summary and conclusions are given. This book was originally a Ph.D. thesis. It describes the results of a research project carried out at the University of Twente, The Netherlands. The project dated from 1987 to 1991 and was sponsored by the Dutch Innovative Research Program (IOP-IC Technology). The author would like to acknowledge the helpful discussions with many colleagues and students at the University of Twente, University of Delft and Philips. Special thanks are given to Prof. Hans Wallinga and Prof. J. Davidse (Delft University of Technology) for fruitful discussions and for their useful and detailed comment on the manuscript. Bram Nauta

12 ANALOG CMOS FILTERS FOR VERY HIGH FREQUENCIES

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