HIGH-RESOLUTION IF-TO-BASEBAND Σ ADC FOR CAR RADIOS

HIGH-RESOLUTION IF-TO-BASEBAND Σ ADC FOR CAR RADIOS

HIGH-RESOLUTION IF-TO-BASEBAND Σ ADC FOR CAR RADIOS by Paulo G. R. Silva National Semiconductor, Delft, The Netherlands and Johan H. Huijsing Delft University of Technology, Delft, The Netherlands

Authors Paulo G.R. Silva National Semiconductor 2628 XJ Delft, The Netherlands pg.silva@ieee.org Johan H. Huijsing Delft University of Technology 2628 CD Delft, The Netherlands j.h.huijsing@tudelft.nl ISBN: 978-1-4020-8163-7 e-isbn: 978-1-4020-8164-4 Library of Congress Control Number: 2008920071 2008 Springer Science + Business Media B.V. No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission from the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Printed on acid-free paper. 987654321 springer.com

To the memory of my grandfather Fiorello Raymundo.

Table of Contents Preface... XI 1. Introduction... 1 1.1 Motivation... 1 1.2 Car Radio History... 5 References... 9 2. DSP Based Radio Receiver Architectures... 11 2.1 Radio Receiver Architectures... 12 2.1.1 Heterodyne and Homodyne Receivers... 12 2.1.2 DSP Based Radio Receiver Architectures... 14 2.2 ADC Performance Metrics... 17 2.2.1 Measures of Resolution... 17 2.2.2 Measures of Linearity... 18 2.3 Desensitization and Blocking... 21 2.4 Image Rejection... 24 2.5 Analog Radio Broadcasting... 29 2.6 Digital Radio Broadcasting... 30 2.7 Integrated Solutions for AM/FM Receivers... 32 References... 37 3. Continuous-Time Σ Modulation... 41 3.1 Basic Principles... 42 3.1.1 Oversampling... 43 3.1.2 Noise Shaping... 46 3.1.3 Anti-alias Filtering... 48 3.2 High-Order Σ Modulators... 50 3.3 Tonal Behaviour... 57 3.3.1 DAC Modulation at f s /2... 59 3.3.2 2 nd -Order Non-linearity... 61 3.4 Clock Jitter... 65 3.4.1 Random Jitter... 65 3.4.2 Deterministic Jitter... 68 References... 69 HIGH-RESOLUTION IF-TO-BASEBAND Σ ADC FOR CAR RADIOS VII

4. Σ ADC Topologies for Radio Receivers... 71 4.1 Lowpass Σ ADCs... 72 4.1.1 Feedback Compensation... 73 4.1.2 Feedforward Compensation... 78 4.1.3 Feedforward and Feedback Compensation... 81 4.1.4 Feedback Compensation with Local Feedforward Path... 84 4.1.5 Resonators and Local Feedback... 87 4.2 IF-to-Baseband Σ ADCs... 90 4.3 Quadrature IF-to-Baseband Σ ADCs... 93 4.4 Bandpass Σ ADCs... 102 4.4.1 Continuous-Time Bandpass Σ Modulators... 103 4.4.2 Continuous-Time Resonators... 106 4.5 Quadrature Bandpass Σ ADCs... 109 4.6 Conclusions... 111 References... 113 5. IF-to-Baseband Σ ADC for AM/FM/IBOC Receivers... 117 5.1 IF-to-Baseband Conversion System... 118 5.2 IF Mixer... 124 5.2.1 Mixer Linearity... 125 5.2.2 Mixer Dynamic Performance... 126 5.2.3 Isolated Mixer Topology... 132 5.2.4 Mixer Driver... 136 5.3 First Integrator... 138 5.3.1 Design of the 1 st OTA To Be Used as a CT Integrator... 140 5.3.2 Design of the 1 st OTA To Be Used as a SC Integrator... 143 5.3.3 1 st OTA Transistor Level Design... 149 5.4 High-Order Integrators and Resonators... 152 5.5 Feedforward Coefficients and Quantizer... 157 5.6 SC Feedback DAC... 159 5.7 Experimental Results... 163 5.7.1 First Prototype... 164 5.7.2 Second Prototype... 171 References... 176 VIII HIGH-RESOLUTION IF-TO-BASEBAND Σ ADC FOR CAR RADIOS

6. Conclusion... 179 6.1 Benchmarking... 179 6.2 Economic Feasibility... 181 References... 183 A. Harmonic Distortion in CT Integrators Using MOSCAPs... 187 A.1 Introduction... 187 A.2 Harmonic Distortion in Differential G m -C Integrators... 189 A.3 Harmonic Distortion in Differential Feedback Integrators... 192 References... 195 B. Noise Analysis of CT Σ Modulators with SC Feedback DAC... 197 B.1 Introduction... 197 B.2 Noise Voltage PSD Across a Switched Capacitor... 199 B.3 Input-Referred Thermal Noise Due to the SC Feedback DAC MOS Switches... 201 B.3.1 Direct Noise Components... 201 B.3.2 Sampled-and-Held Components... 203 B.3.3 Input-Referred Noise... 204 B.4 Input-Referred Thermal Noise Due to the SC Feedback DAC Reference Voltage... 205 B.5 Input-Referred Thermal Noise Due to the OpAmp... 206 B.6 Conclusion... 208 References... 208 List of Acronyms... 209 List of Symbols... 211 Index... 213 About the Authors... 217 HIGH-RESOLUTION IF-TO-BASEBAND Σ ADC FOR CAR RADIOS IX

Preface This book presents the design of a high dynamic-range (DR) continuous-time (CT) IF-to-baseband Σ modulator for AM/FM receivers. The main challenge of this work was to achieve 118dB DR in 3kHz (AM mode) and 98dB DR in 200kHz (FM mode). At the same time, high linearity (IM 3 >85dB) was required to allow multi-channel digitization in AM mode. The designed ADC also complies with the IBOC (In-Band, On-Channel) standard for digital audio broadcast. In Chapter 2, an overview of the most important radio receiver architectures is presented. The evolution of CMOS technology enabled the incorporation of digital signal processing into car radios. The closer the ADC is to the antenna; the more signal processing functions like filtering and demodulation can be implemented in the digital domain. As a result, more resolution and linearity are demanded from the ADC. The most important ADC performance metrics, and concepts like desensitization, blocking and image rejection are also reviewed in this chapter Chapter 3 starts with a review of the basic principles of CT Σ modulation: oversampling, noise shaping and intrinsic anti-alias filtering. The stability and the tonal behaviour in high-order loop filters are also discussed. Non-idealities in the modulator implementation may cause down-conversion of strong tones and quantization noise from nearby f S /2 to the low-frequencies, reducing the modulator DR. This chapter ends with a discussion about the effects of clock jitter in the performance of CT Σ modulators. A discussion about Σ ADC topologies for DSP based radio receivers is presented in Chapter 4. The major characteristics of lowpass, IF-to-baseband, quadrature IF-to-baseband, bandpass and quadrature bandpass Σ ADCs are compared. An IF-to-baseband Σ ADC consists of a mixer integrated with a lowpass modulator for IF digitization. Two IF-to-baseband ADCs in parallel, whose mixers are driven in quadrature, HIGH-RESOLUTION IF-TO-BASEBAND Σ ADC FOR CAR RADIOS XI

Preface implement a quadrature IF-to-baseband ADC. It is shown in Chapter 4 how mismatches among the complex integrators building blocks translate into the leakage of quantization noise power from the image band to the signal band, and vice-versa. Finally, a comparison among these architectures is presented. Chapter 5 describes the system-level design and the circuit implementation of a single-bit 5 th -order quadrature CT IF-to-baseband Σ ADC for AM/FM/IBOC receivers. This 118dB DR ADC enables the realization of a car radio that does not require an IF VGA, neither an AM channel selection filter. Because of the multi-channel AM digitization, most of the AM channel selection can be performed in the digital domain. Finally, Chapter 6 presents the conclusions of this work and a discussion about the economic feasibility of the proposed radio receiver architecture. This book ends with two appendixes. In appendix A, an analysis of the harmonic distortion in CT integrators employing MOSCAPs is presented. The input-referred noise of CT Σ modulators with switched-capacitor feedback is calculated in Appendix B. Paulo G. R. Silva Johan H. Huijsing Delft, October 2007. XII HIGH-RESOLUTION IF-TO-BASEBAND Σ ADC FOR CAR RADIOS