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Smart Sensor

ID: TASIC002 • Posted in Application Notes • April 28, 2008 • 9:00am
PDF: Smart Sensor
Market: Industrial
Target Platform: VCA-4
Application: Smart Sensors add value to transducer data enabling and supporting distributed processing/decision making. By providing standardized engineering unit information, self-identification and time-stamping, smart sensors simplify the integration of transducers in a networked environment.
Figure 1

Smart Sensor Market

Smart Sensor is an umbrella term used to describe the addition of local intelligence to transducer information.

In the past, hooking up a transducer required dedicated point-to-point routing. The host processor needed to contain all of the information about the transducer before working with a sensor. A smart sensor contains interfaces to the transducer, analog processing, non-volatile memory that stores ‘datasheet’ information about the sensor, digital processing, and analog/digital communication links.

The smart sensor concept has been expressed in the family of IEEE1451 standards. These standards add Transducer Electronic Data Sheet (TEDS) information to the local sensor so that it can identify itself to the sensor network and support a plug-and-play approach to sensor integration. When a smart sensor is plugged into an acquisition network, the sensor identifies itself to the network, states what types of information will be reported, the engineering units used to report the data, manufacturer’s identification information, and extended manufacturer/user data.

Developers of smart sensor solutions are looking for these plug and play benefits while keeping transducer cost low and minimize power consumption.

Manufacturers are looking for:

Plug-and-Play - smart sensors enable easy system integration
Integration - reduce size and weight to support portable applications
Power Savings - required for portable applications
Sensor > to > Information

Transducer > Analog Interface > Data Converter > DSP > Non-volatile > Digital Communications Link

Transducers

Analog

Converters

Digital

Communication
  • Voltage
  • Current
  • Bridge
  • Vibration
  • Gas
  • Light
  • Shock
  • Strain
  • Humidity
  • pH
  • Pressure
  • Ultrasonic
  • Weight
  • Acceleration
  • Direction
  • Magneto-resistive
  • Temperature
  • Tilt
  • Level
  • Location
  • Input Buffer
  • Low Noise Input
  • Programmable Gain
  • Instrumentation Amplifier
  • Filtering: low-pass, band-pass, notch, high-pass
  • Analog multiplexing
  • Switched Capacitor Circuits
  • Chopper-stabilized Circuits
  • Correlated Double Sampling
  • Silicon Temperature Sensor
  • Comparator
  • Integrator
  • Excitation DAC
  • Voltage reference DAC
  • Pulse Width Modulator
  • Analog to Digital Converter
  • Dual-Slope
  • M-Slope
  • Delta Sigma
  • Successive Approximation
  • Transducer-to Voltage Converter
  • Bias Generators
  • Voltage Reference Network
  • Decimation Filter
  • FIR Filter
  • IIR Filter
  • State Machines
  • Data Logging
  • Microprocessor
  • Non-Volatile Memory
  • Counter/Timers
  • Transducer-to- Frequency Converter
  • Custom Logic
  • Digital Signal Processing
  • IEEE1451.4 TEDS
  • SPI
  • IIC
  • UART
  • Differential I/O
  • Wireless Interface
  • RFID
  • LIN
  • CAN
  • USB

Triad VCA Building Blocks for Smart Sensor Applications

Smart Sensor

System Requirements

Triad VCA Building Blocks
Low-Noise
  • Low Power Low Noise Op-Amp
  • 2Vp-p input referred noise
  • Correlated Double Sampling Amplifiers
High Gain to amplify signals prior to A/D conversion
  • Programmable Gain Amplifiers
Band Pass Filter to remove out of band noise
  • Continuous Time, Switched Capacitor Filters
  • Digital Decimation Filters
Low Power for battery powered applications
  • Low Power Analog Tiles
  • Low Power Band Gap
  • Low Power Digital with Sleep Mode Power Savings
High Resolution A/D Conversion
  • 16-bit Sigma Delta ADC
  • Fully Differential Architecture
  • 2nd, 3rd, 4th - order modulators
Bridge Biasing and Excitation
  • 10-bit Reference DACs
  • 12-16 bit Pulse Width Modulators (PWM)
Serial Communication to transfer digitized electrode data to a host computer for display
  • SPI, IIC, UART, LIN, Custom
TEDS - Transducer Electronic Datasheet
  • 8Kbytes of EEPROM
  • 100K Write Cycles, 20 Year Data Retention
  • EEPROM can be partitioned between program store, calibration data, and TEDS.
  • Each data section has independent write protection
Local Intelligence “Embedded Sensor Processor”
  • Complete 8051 Microprocessor Subsystem
  • 25MHz, 1-2 Cycle Pipelined 8051 Architecture
  • Configurable ROM, EEPROM, Program RAM & Data RAM solutions
  • Serial Debug Interface
  • Interrupts, Watchdog, Power-Down
  • Power Saving Slow Clocking Mode
Reduced Development NRE
  • Single Mask to configure a custom ASIC
  • Support for Customized Smart Sensor Solution
  • Single Mask Fabrication Time ß 4 Weeks
  • No Full-Custom Layout Required
  • Accelerate Development with Triad Proven IP
Reduced Development Time
Reduced Risk
  • Triad has domain expertise in Smart Sensor design and Triad engineers are available to take your idea to full-production.
  • Triad engineers have developed over 130 successful ASICs.
  • 10+ years of experience per Triad Engineer

IEEE1451.4 Smart Sensor Triad VCA ASIC

Utilizing the VCA-4 platform, an IEEE1451.4 compatible Smart Sensor ASIC can be realized as shown in Figure 2 below. This ASIC provides the following features:

  • Multi-Channel Analog Inputs
  • Programmable Gain Amplifiers - Digitally Programmable Gain
  • Low-Noise Input Amplifiers
  • Single-Ended and Differential Inputs
  • Analog Multiplexing
  • Dual 10-bit DACs useful for external biasing or bridge excitation
  • 16-bit Differential Sigma-Delta Analog to Digital Converter
  • Digital Decimation and FIR Filter
  • Integrated Single Cycle 8051 Microprocessor
    • RAM 3.75KB
    • EEPROM 8KB
    • Debug Interface
    • UART
    • Watchdog
  • 32KHz PLL capable of generating a master clock from 32KHz to 2MHz - ideal for low-power sleep modes followed by high-speed processing and back to sleep
  • UART off-chip Communication Link

This example implementation of a Smart Sensor Interface on the VCA-4 array provides high precision, low power analog processing, 16-bit analog to digital conversion, and a flexible 8051 integrated microprocessor subsystem to effectively transform raw transducer signals into useful system information. The transducer may provide raw temperature samples but the system is only interested in knowing when the temperature has gone above TEMP_MAX or below TEMP_MIN. Instead of sending the raw sensor data upstream to a central processor to manage, the local smart sensor processor reads temperature data, averages the data, and compares the results to the programmable TEMP_MAX and TEMP_MIN trigger levels. When the trigger levels are exceeded, the smart sensor sends a report to a networked central processor informing the processor that a particular sensor in the network has tripped a temperature alarm.

Non-Volatile Memory Uses in a Smart Sensor ASIC

  • Reprogrammable Microcontroller
  • Modify the 8051 program to accept data from different sensors enabling the ASIC to serve in more applications
  • Extend the functionality of the Smart Sensor in the field via a boot-loader update of the program code over the UART serial link
  • Calibration Data
  • Temperature Compensation of Transducer Data
  • Linearize Sensor Data
  • Transducer Electronic Datasheet
    • Manufacturer ID
    • Sensor Serial Number
    • Sensor Type
    • Sensor Version
    • Amplifier Gain Settings
    • Analog and Digital Signal Path Settings
    • Sensor Data Format - Express results in engineering units
    • User defined data
Figure 2
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