Basics of Sensor Compensation for Piezoresistive Sensors January 21, 2013 Randy Frank

Agenda Steps toward smart sensors Wheatstone bridge Amplification Calibration, linearization and signal integrity techniques for piezoresistive sensors More complex piezoresistive interfaces

Levels of Intelligent Sensor Processing Knowledge Extraction Layer 4 Information Enhancement Layer 3 Wireless or Wired Bus Communications to Other intelligent systems & Smart Sensors System Awareness Sensor Compensation Layer 2 Data Acquisition Layer 1 Source: Microchip Technology

Accurate Data & Better Decisions Knowledge Extraction Pattern Recognition Classification Prediction Adaptive Filtering Information Enhancement Frequency Domain Noise Removal Sensor Fusion Sensor Compensation Calibration Linearization Signal Integrity Diagnostics Data Acquisition Transducer Amplification Low Pass Filtering A/D Conversion Source: Microchip Technology

Silicon Piezoresistive Pressure Sensors Eo = E∆R R

Span Understanding Smart Sensors

Best Fit Straight Line Offset http://www.allsensors.com/engineering-resources/white-papers/linearity-measurements-pressure-sensors

Effect of Temperature Offset Temperature Shift (0°C-70°C), Typical: ±0.1 mV Temperature Effect on Resistance (0°C-70°C), typical: 2800 ppm/°C Temperature Effect on Span (0°C-70°C), Typical: -1900 ppm/°C http://www.allsensors.com/products/BLVR-L01D#product_series For All Sensors BLVR-L01D

Constant Current Source Amplifier http://www.maximintegrated.com/app-notes/index.mvp/id/871 Also check out http://www.meas-spec.com/downloads/A_Simple_Pressure_Sensor_Signal_Conditioning_Circuit.pdf And http://www.analog.com/library/analogDialogue/archives/38-05/AD8555.html

Quad Op Amp Circuit TI’s TLV2474 Rail-to-rail http://www.ti.com/lit/an/slyt144/slyt144.pdf Rail-to-rail

Instrumentation Amplifier Typical key specifications: Operating voltage range Rail to rail operation Common mode rejection ratio (CMMR) Input Voltage Noise Density Power supply rejection ratio (PSRR)

Instrumentation Amplifier Example Microchip Technology’s MCP6N11 Operating Voltage Range: 1.8 to 5.5V Input Voltage Noise Density (nV/rt(Hz)) 35 typ PSRR min 94 dB CMRR min 94 dB Piezoresistive example http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en555897 Good background info: http://ww1.microchip.com/downloads/en/appnotes/00990a.pdf

1%-Accurate Signal Conditioner Maxim Integrated MAX1450

Signal Conditioner for Piezoresistive Sensors MAX1450 http://www.maximintegrated.com/datasheet/index.mvp/id/1867?ver=C&utm_expid=50713806-2&utm_referrer=http%3A%2F%2Fwww.maximintegrated.com%2Fpst%2Frun.mvp%3Fq%3Dmax1450 An evaluation kit is available: MAX1450EVKIT

Piezoresistive Interface ZMDI ZSC31010 Sensor Signal Conditioner CMOS integrated circuit Designed for resistive bridge sensors Digitally calibrate offset and gain Internal temperature compensation and detection Development kit available http://www.zmdi.com/zsc31010

Piezoresistive Interface ZMDI ZSC31010 OWI – one wire interface http://www.zmdi.com/zsc31010 ZMDI’s ZACwire™ serial interface to the host computer and is easily mass calibrated in a Windows™ environment Calibration performed by eeprom – no external trimmed components

Pressure Sensor Signal Conditioning Interface Texas Instruments TPIC83000-Q1 http://focus.ti.com/download/auto/newsletters/autosolutions_09-q4.htm http://www.ti.com/product/TPIC83000-Q1

TI’s WEBENCH Sensor Designer Provides Analog Interface Family for: Pressure sensors Temperature Load sensors pH sensors Chemical & gas sensors

TI’s AFE AFE: Analog Front End For resistive bridge sensors LMP90100 Temperature, Pressure, Load, Force and more A complete signal path solution: sensor-MCU Multi-channel with 16- or 24-bit Sigma Delta ADC core Flexible, programmable mux (4 differential, 7 single-ended, or a combination inputs) Continuous background sensor diagnostics For resistive bridge sensors http://www.ti.com/product/lmp90100

TI’s AFE LMP90100 http://www.ti.com/product/lmp90100

Summary For piezoresistive sensors Several good sources of information exist Simple circuits Complex circuits Design kits and tools simplify design-in

Topics Later This Week Tuesday Basics of Sensor Compensation for Capacitive Sensors Wednesday A case study of smart sensor development Thursday Transitioning from analog sensing to the digital control world Friday Today’s smart sensors