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  • INTEGRATED SMART SENSORS

  • INTEGRATED SMART SENSORS DESIGN AND CALIBRATION

    by

    Gert van der Horn University of Delft

    and

    Johan L. Huijsing University of Delft

    SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.

  • A C.I.P. Catalogue record for this book is available from the Library of Congress.

    ISBN 978-1-4419-5016-1 ISBN 978-1-4757-2890-3 (eBook) DOI 10.1007/978-1-4757-2890-3

    Printed on acid-free paper

    AII Rights Reserved 1998 Springer Science+Business Media Dordrecht

    Originally published by Kluwer Academic Publishers in 1998 Softcover reprint of the hardcover 1 st edition 1998

    No part of the material protected by this copyright notice may be reproduced or utilized in any fonn or by any meanS, electronic or mechanical,

    including photocopying, recording or by any information storage and retrieval system, without written pennission from the copyright owner.

  • Table of Contents

    1 lntroduction 1 1.1 Introduction .............................................................. 1 1.2 Sensors and actuators ............................................... 2 1.3 Integrated smart sensors ........................................... 5 1.4 Measurement errors and correction .......................... 6

    l.4.1 Process variations and time variations .......................... 7 1.4.2 Calibration ..................................................................... 8 1.4.3 Se1f-testing ................................................................... Il l.4.4 Se1f-calibration ............................................................ 13 l.4.5 Redundancy improvement Of feedforward testing ...... 15 l.4.6 ConcJuding remarks ..................................................... 16

    1.5 Objective and Organization ................................... 16 1.5.1 Objective ...................................................................... 16 1.5.2 Organization ................................................................ 17 1.5.3 Design constraints ....................................................... 17

    References ........................................................................... 19

    2 lntegrated Smart Sensor Concept 21 2.1 Introduction............................................................ 21 2.2 Silicon sensors..... ................................................... 22

    2.2.1 Temperature sensor ..................................................... 22 2.2.2 Pressure sensor ............................................................ 23 2.2.3 Measurement errors ..................................................... 25

    INTEGRATED SMART SENSORS: Design and Calibration v

  • Table of Contents

    3

    2.3 Analog Interface circuits ......................................... 27 2.3.1 Temperature sensor readout ........................................ 27 2.3.2 Pressure sensor readout ............................................... 32

    2.4 Analog-to-Digital conversion ................................. 33 2.4.1 Sigma-delta converter ................................................. 34

    2.5 Digital bus or microcontroller interface ................. 39 2.5.1 Microcontroller compatible interfaces ........................ 39 2.5.2 Smart Sensor bus interfaces ........................................ 40

    2.6 Integrating a calibration function in the smart sensor concept ................................................................................. 43 2.6.1 Error sources in the smart sensor signal path .............. 43 2.6.2 Conventional sensor calibration techniques ................ 44 2.6.3 Correction of the sensor signal transfer ...................... 45 2.6.4 Calibration memory .................................................... 46

    References ........................................................................... 47

    Calibration and Iinearimtion Techniques 51 3.1 Introduction ............................................................. 51

    3.1.1 Errors in the sensor transfer curve .............................. 51 3.1.2 Systematic and random errors ..................................... 53 3.1.3 Linear and nonlinear errors ......................................... 55 3.1.4 Normalized sensor transfer functions .......................... 56

    3.2 Linearization ........................................................... 58 3.2.1 Sensor characteristic linearization ............................... 59 3.2.2 Linearization based on a look-up table ....................... 60 3.2.3 Linearization based on piecewise-linear interpolation 63 3.2.4 Linearization based on piecewise-polynomial or spline

    interpolation ................................................................ 67 3.2.5 Linearization based on curve fitting ............................ 70 3.2.6 Linearization based on error minimization ................. 73 3.2.7 Conc1usion ................................................................... 75

    VI INTEGRATED SMART SENSORS: Design and Calibration

  • Table of Contents

    3.3 Progressive polynomial calibration method ........... 76 3.3.1 One-dimensional functions .......................................... 77 3.3.2 Two-dimensional functions ......................................... 84 3.3.3 Multi-dimensional functions ....................................... 88

    3.4 Conclusion ............................................................. 89 References ........................................................................... 90

    4 Calibration using Analog Signal Processing 93 4.1 Introduction ............................................................ 93 4.2 Conventional sensor calibration ............................. 94

    4.2.1 Resistor trimming ........................................................ 94 4.2.2 Programmable resistor-arrays ...................................... 96

    4.3 Analog calibration circuits ..................................... 96 4.3.1 Classical offset and full-scale calibration .................... 98 4.3.2 Classical cross-sensitivity calibration .......................... 99 4.3.3 Improved analog calibration circuit... ........................ 102

    4.4 Classical pulse-modulated calibration .................. 104 4.5 Analog implementation of a polynomial

    calibration . . . . . . . . . . . . . . . . . . . . . . . .. 106 4.5.1 System configuration ................................................. 106 4.5.2 Analog current multiplier .......................................... 108 4.5.3 Programmable current divider DAC ......................... 111 4.5.4 VI-converters and IV-converters ............................... 113 4.5.5 System implementation ............................................. 116 4.5.6 System operation ....................................................... 117 4.5.7 Realization ................................................................. 121

    4.6 Conclusion ............................................................ 124 References ................ o .... o .......... o .... o o .. o .. o ....................... o .... 126

    INTEGRATED SMART SENSORS: Design and Calibration Vll

  • Table of Contents

    5 Calibration using Sigma-Delta Analog-to-Digital Conversion 127 5.1 Introduction ........................................................... 127 5.2 Sigma-delta AD-converters .................................. 128

    5.2.1 Principle of oversampling ......................................... 129 5.2.2 Principle of noise shaping ............. ........... ............. .... 130 5.2.3 Principle of decimation ............................................. 136 5.2.4 Transfer from analog input to digital output ............. 139

    5.3 Alteration of the sigma-delta transfer ................... 140 5.3.1 Digital sigma-delta bitstream generator .................... 140 5.3.2 Modulating the input signal for gain calibration ....... 143 5.3.3 Modulating an additional signal for offset

    calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 5.3.4 Sigma-delta calibration configurations ..................... 148

    5.4 Implementation of the sigma-delta AD-converter 152 5.4.1 Differential integrator amplifier ................................ 153 5.4.2 Clocked comparator .................................................. 155 5.4.3 Sigma-delta converter ............................................... 157 5.4.4 Digital decimation filter implementation .................. 159

    5.5 Smart temperature sensor realizations .................. 160 5.5.1 Smart temperature sensor with calibration and IS2 bus in-

    terface ............................................... ......................... 161 5.5.2 Temperature sensor with linearity calibration ........... 165

    5.6 Conclusion ............................................................ 168 References... .... ........ ...... ..... ....... ...... ..... ....... ........... ........... 169

    viii INTEGRATED SMART SENSORS: Design and Calibration

  • 6 Calibration using Digital Signal Processing

    Table of Contents

    173

    6.1 Introduction ........................................................... 173 6.2 Hardware implementation ..................................... 174 6.3 Software implementation ...................................... 178

    6.3.1 Sensor system configuration ...................................... 178 6.3.2 Calibration algorithm ................................................. 179 6.3.3 Calibration program ................................................... 189 6.3.4 Future work ............................................................... 191

    6.4 Conclusion ............................................................ 191 References .