High-Resolution If-To-Baseband ΣΔ Adc For Car Radios

222 Pages·2008·5.5 MB·English

by  Paulo G. R. Silva

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 Johan H. Huijsing
National Semiconductor Delft University of Technology
2628 XJ Delft, The Netherlands 2628 CD Delft, The Netherlands
[email protected] [email protected]
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
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Printed on acid-free paper.
9 8 7 6 5 4 3 2 1
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
2.1.1Heterodyne and Homodyne Receivers ........................................ 12
2.1.2DSP Based Radio Receiver Architectures ................................... 14
2.2 ADC Performance Metrics ................................................................... 17
2.2.1Measures of Resolution ............................................................... 17
2.2.2Measures 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
Σ∆
3. Continuous-Time Modulation .................................... 41
3.1 Basic Principles .................................................................................... 42
3.1.1Oversampling .............................................................................. 43
3.1.2Noise Shaping .............................................................................. 46
3.1.3Anti-alias Filtering ....................................................................... 48
3.2 High-Order Σ∆ Modulators .................................................................. 50
3.3 Tonal Behaviour ................................................................................... 57
3.3.1DAC Modulation at f /2............................................................... 59
s
3.3.22nd-Order Non-linearity................................................................ 61
3.4 Clock Jitter ............................................................................................ 65
3.4.1Random Jitter ............................................................................... 65
3.4.2Deterministic Jitter ...................................................................... 68
References ............................................................................................ 69
HIGH-RESOLUTION IF-TO-BASEBANDΣ∆ ADC FOR CAR RADIOS VII
Σ∆
4. ADC Topologies for Radio Receivers .................... 71
4.1 Lowpass Σ∆ ADCs ............................................................................... 72
4.1.1Feedback Compensation ............................................................. 73
4.1.2Feedforward Compensation ........................................................ 78
4.1.3Feedforward and Feedback Compensation ................................. 81
4.1.4Feedback Compensation with Local Feedforward Path .............. 84
4.1.5Resonators 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
4.4.1Continuous-Time Bandpass Σ∆ Modulators .............................. 103
4.4.2Continuous-Time Resonators ..................................................... 106
4.5 Quadrature Bandpass Σ∆ ADCs .......................................................... 109
4.6 Conclusions ......................................................................................... 111
References ........................................................................................... 113
Σ∆
5. IF-to-Baseband ADC for AM/FM/IBOC
Receivers ................................................................................................. 117
5.1 IF-to-Baseband Conversion System .................................................... 118
5.2 IF Mixer ............................................................................................... 124
5.2.1Mixer Linearity .......................................................................... 125
5.2.2Mixer Dynamic Performance ..................................................... 126
5.2.3Isolated Mixer Topology ............................................................ 132
5.2.4Mixer Driver ............................................................................... 136
5.3 First Integrator ..................................................................................... 138
5.3.1Design of the 1st OTA To Be Used as a CT Integrator .............. 140
5.3.2Design of the 1st OTA To Be Used as a SC Integrator ............... 143
5.3.31st 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
5.7.1First Prototype ............................................................................ 164
5.7.2Second Prototype ....................................................................... 171
References ........................................................................................... 176
VIII HIGH-RESOLUTION IF-TO-BASEBANDΣ∆ 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.1Introduction ........................................................................................ 187
A.2Harmonic Distortion in Differential G -C Integrators ....................... 189
m
A.3Harmonic Distortion in Differential Feedback Integrators ................. 192
References .......................................................................................... 195
Σ∆
B. Noise Analysis of CT Modulators with SC
Feedback DAC ...................................................................................197
B.1Introduction ........................................................................................ 197
B.2Noise Voltage PSD Across a Switched Capacitor .............................. 199
B.3Input-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.4Input-Referred Thermal Noise Due to the SC Feedback DAC Reference
Voltage ..................................................................................................... 205
B.5Input-Referred Thermal Noise Due to the OpAmp ............................ 206
B.6Conclusion .......................................................................................... 208
References .......................................................................................... 208
List of Acronyms......................................................................... 209
List of Symbols.............................................................................. 211
Index.................................................................................................... 213
About the Authors..................................................................... 217
HIGH-RESOLUTION IF-TO-BASEBANDΣ∆ 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 >85dB) was required to allow multi-channel
3
digitization in AM mode. The designed ADC also complies with the
IBOC (In-Band, On-Channel) standard for digital audio broadcast.
In Chapter2, 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
Chapter3 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 /2
S
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 Chapter4. The major characteristics of lowpass,
IF-to-baseband, quadrature IF-to-baseband, bandpass and quadrature
bandpassΣ∆ 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-BASEBANDΣ∆ ADC FOR CAR RADIOS XI
Preface
implement a quadrature IF-to-baseband ADC. It is shown in Chapter4
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.
Chapter5 describes the system-level design and the circuit
implementation of a single-bit 5th-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, Chapter6 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-BASEBANDΣ∆ ADC FOR CAR RADIOS