ADI Automotive Sensor and Sensor Interface Solution

Application Description
Automobiles must become increasingly greener to meet emerging legislation for improved fuel economy and reduced emissions. These requirements can only be fulfilled by improving the efficiency of the traditional internal combustion engine, achieved through improvements in combustion, sensing, and control, leading to the need for higher sensor and signal conditioning accuracy and integration. There are typically more than 100 sensors in a vehicle, and sensors can typically be categorized into six functions, including pressure, current, capacitance, position, speed, and temperature sensors.

System Requirement and Design Challenge
Vehicle sensors are used across multiple applications in powertrain, chassis/safety and body systems. Improvements in fuel economy, emissions and vehicle performance need to be improved simultaneously in power train systems. For sensors, this results in significant performance improvements and/or features that are challenging to achieve in areas such as dynamic range, accuracy, diagnostics, and robustness (EMC, ESD, temperature, etc.).


Pressure Sensor
Many pressure sensors are required in high pressure and harsh environments to measure air or fluid pressures. Some power train examples include in-cylinder, transmission oil, diesel common rail, GDI fuel, diesel particulate filter (DPF), and exhaust gas recirculation (EGR) pressure. Safety applications
include brake fluid and occupant detection weight or pressure. High pressure and harsh environment applications require that the sensor element (capacitive or piezo-resistive) is separated from the signal conditioning IC. A piezo-resistive (strain gauge) solution, can, for example, measure pressure ranges up to 2800 bar.

The strain gauge technology is based on a resistive bridge. Four strain gauges are attached to a diaphragm to form a diaphragm-type pressure transducer.The output signal is as small as 10 mV. The system errors include mechanical output, thermal output, tolerance, and gauge factor errors. The total errors can reach up to 100% FSR. Hence, the conditioning circuit must be highly accurate and have low drift. Multiple-variable compensations related to gain, offset, temperature, and linearity are also required.

Pressure sensors are placed mainly in harsh environments. A typical operating temperature range is −40°C to +125°C and, in some cases, up to 150°C. The sensors also require high EMC capability and diagnostic functions.


Current Sensor
To improve fuel economy and energy management, the position of the solenoid valves in the fuel injection system and automatic gear boxes must be precisely controlled. In addition, electric motor current for power “on demand” must be monitored more accurately. High accuracy, a low offset (an offset needs <5 mV and an offset drift needs <20 μV), a high bandwidth (some cases require up to 500 kHz), a wide common-mode voltage range (up to 65 V), and a wide operating temperature range (up to 125°C) in a harsh environment comprise the typical design challenges.


Capacitance Sensor
Capacitance sensors have advantages such as their low system cost, different shape feasibilities, and low power consumption. They are typically applied as proximity detectors in a keyless entry system, rain detectors, humidity sensors, and fuel level/quality sensors. Capacitance sensors are sensitive to
environmental changes and, thus, require a high resolution, accurate, adjustable common-mode capacitance, and EMI immunity.


Position and Speed Sensors
In EPS and BLDC/PMSM motor control applications, position/speed measurement requires a fast response, good accuracy (up to 0.1°), robustness, and low
drift. Diagnostic functions are also needed.


Temperature Sensor
Wide temperature ranges and high accuracies are required in some high temperature automotive applications such as transmission control. A typical temperature range is −40°C to +150°C and, in some cases, up to 175°C. Further, an accuracy of ±2°C or ±1°C is required.


Solutions from Analog Devices, Inc.
With long term good relationships with worldwide leading automotive suppliers, plus the experience of high performance signal processing, high reliability, and
quality product development, Analog Devices (ADI) is the leader and is able to provide optimized solutions to meet these challenges.