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84 Understanding Smart Sensors4.3.2 Integrated Active ElementsIntegrating the amplification and signal conditioning directly on the sensorcan be accomplished by the use of combined micromachining and microelectronics.The circuit of a fully signal conditioned pressure sensor is shown inFigure 4.11(a). The additional circuitry is integrated on the sensor using thesilicon area that is required to provide the mechanical support for the diaphragm[22]. The die size for the fully signal conditioned unit is 0.145 inch by0.130 inch. The diaphragm and piezoresistive element account for 20% of thedie, and the signal conditioning circuitry is 80%, including the area requiredfor wire bond pads. A quad operational amplifier frequently used for sensoroutput amplification is the LM324. The area of silicon in the LM324 is about0.050 inch by 0.050 inch. The sensor without signal conditioning is a 0.120-inch by 0.120-inch chip. In that case, the electronics has been combined withthe sensor with a very small increase in the total chip area because the mechanicalsupport for the diaphragm has been utilized. Common pressure ranges anda standard interface to 5V dc ADC allow the integrated approach to satisfy anumber of application requirements and justify the cost of the integrateddesign. The integrated sensor easily interfaces to an MCU with an onboardADC, as shown in Figure 4.11(b). The 50-pF capacitor and 51-kΩ resistor arerecommended as a decoupling filter.A more recent circuit design met the target specifications with one lessstage in the amplification circuitry than the earlier design [23]. As shown inFigure 4.12, it uses fewer resistors and is easier to trim. In addition a highersource/sink current can be obtained in the new design. Initial indications arethat improvement of at least 10 times has been obtained. The output stage hasbeen designed to drive CMOS A/D inputs from 0.2V to 4.7V (typical values)with a 5V supply.Along with the new circuit, a revised trim algorithm was developed.Although the basic principles are similar to the earlier version, there are severalimportant improvements. One of the most important is the balanced design,which allows for bidirectional trimming of all parameters, and a more independenttrim of each parameter. On the old circuit, parameters such as temperaturecoefficient of offset (Tco) and gain could be trimmed in only onedirection. If processing variations resulted in the initial value of those parametersbeing beyond the target values, the device could not be trimmed. Additionally,many parameters had to be trimmed with an iterative process in whichseveral parameters were roughly trimmed, and then they were all trimmedagain, to reach the final target. Any adjustment of one resistor affected morethan one parameter and limited the overall system accuracy. For the newdesign, all parameters can be trimmed in either direction, and each one is
Getting Sensor Information Into the MCU 85R sV 1R 1R 3−V pR 11R gV sourceV exV s−R toV 2V+O A1R 4V aV 4Q 4R 13GndQ outV outOV s+R 2A2R 5+R 8R 9O A3−R 10+−(a)V rhV ddMPX51000MC68HC05B6exV2V1VccGndVoutP1CH1PORT DV rlV ss(b)Figure 4.11 (a) Integrated piezoresistive pressure sensor circuit and interface to MCU, and(b) sensor interfaced to MCU.
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Understanding Smart SensorsSecond E
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Library of Congress Cataloging-in-P
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ContentsPrefacexix1 Smart Sensor Ba
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Contentsix3.3.3 Hall Effect 603.3.4
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Contentsxi5.8 Summary 116References
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Contentsxiii8.3.1 Surface Acoustica
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Contentsxv11.1.1 Integration and Me
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Contentsxvii14.4.4 Electrostatic Me
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PrefaceThe number one challenge fac
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Prefacexxifor well over 6 years. A
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2 Understanding Smart Sensorsobserv
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4 Understanding Smart Sensorssmart
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6 Understanding Smart Sensorsto pro
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8 Understanding Smart Sensorsinclud
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10 Understanding Smart SensorsLevel
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12 Understanding Smart Sensorsuser
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14 Understanding Smart Sensorstechn
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16 Understanding Smart Sensorschang
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18 Understanding Smart Sensorstechn
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20 Understanding Smart Sensors Surf
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22 Understanding Smart Sensorssecon
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24 Understanding Smart SensorsSilic
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26 Understanding Smart SensorsSilic
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28 Understanding Smart SensorsSacri
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30 Understanding Smart Sensors2.4.3
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32 Understanding Smart Sensorsmeasu
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Communications for Smart Sensors 13
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7Control TechniquesA machine is int
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Control Techniques 151Table 7.1Type
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Control Techniques 153otherwise tak
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Control Techniques 155consisting of
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Control Techniques 157Supplied byap
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Control Techniques 159InputX1Synaps
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Control Techniques 1617.6 Adaptive
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Control Techniques 163ObserverHB−
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Control Techniques 165linear-vector
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Control Techniques 1677.7.2 Combine
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Control Techniques 169Domain-type s
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Control Techniques 171[19] De Silva
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8Transceivers, Transponders, andTel
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Transceivers, Transponders, and Tel
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9MEMS Beyond Sensors“And these ot
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MEMS Beyond Sensors 203would not ex
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MEMS Beyond Sensors 205PyrexSilicon
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MEMS Beyond Sensors 207(a)IFluxIIMa
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MEMS Beyond Sensors 209InletThermop
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MEMS Beyond Sensors 211Figure 9.8 A
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MEMS Beyond Sensors 2139.3.2 Microo
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MEMS Beyond Sensors 215Over-range p
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MEMS Beyond Sensors 217+ 10°− 10
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MEMS Beyond Sensors 219achieved wit
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MEMS Beyond Sensors 221Methods for
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MEMS Beyond Sensors 223Figure 9.19
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MEMS Beyond Sensors 225[21] Tortone
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10Packaging, Testing, and Reliabili
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Packaging, Testing, and Reliability
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11Mechatronics and Sensing SystemsP
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Mechatronics and Sensing Systems 25
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12Standards for Smart SensingThe la
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Standards for Smart Sensing 275Netw
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Standards for Smart Sensing 277NCAP
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Standards for Smart Sensing 279Proc
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Standards for Smart Sensing 281PID
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Standards for Smart Sensing 283•
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Standards for Smart Sensing 285•
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Standards for Smart Sensing 287Tabl
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Standards for Smart Sensing 289perf
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Standards for Smart Sensing 2911 0
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Standards for Smart Sensing 293obje
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Standards for Smart Sensing 295Mult
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13The Implications of Smart SensorS
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The Implications of Smart Sensor St
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14The Next Phase of Sensing Systems
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The Next Phase of Sensing Systems 3
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List of Acronyms and Abbreviations3
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List of Acronyms and Abbreviations
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Glossaryablationvaporization of mat
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Glossary 353buscalibrationconnectio
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Glossary 355end point straight line
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Glossary 357data transmission and p
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Glossary 359multiplexer device that
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Glossary 361repeatability the maxim
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Glossary 363spread spectrum techniq
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Glossary 365transducer a device con
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Selected BibliographyBooks and Jour
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Selected Bibliography 369Northeaste
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Selected Bibliography 371Miscellane
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About the AuthorRandy Frank is a te
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Index4-to 20-mA signal transmitter,
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Index 377definitions, 119-20introdu
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Index 379HVAC, 318-19MCU with integ
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Index 381Linearization, 108Linear p
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Index 383in chemical measurements,
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Index 385Ratiometricity, 56Reactive
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Index 387IC fabrication, 19micromec
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Index 389Transducer-independent int
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