Walter Czarnocki

Monolithic Pressure Sensor System with Digital Signal Processing

Most high volume applications of automotive pressure sensors have historically used some form of analog signal conditioning circuit to calibrate and compensate the silicon piezoresistive sensor element that has dominated many of these applications. This signal conditioning approach has often been implemented with some type of laser trimming to provide the appropriate circuit adjustments. Improvements on this approach have been introduced where electrical programming (e. g. fused links or nonvolatile memory) has been used to calibrate the circuit. However, even digital implementations of these calibration methods still rely on a core analog signal processor, thus providing only a discrete-analog solution to the sensor signal conditioning problem. This paper describes a monolithic pressure sensor integrated circuit that uses a custom, dedicated digital signal processor and nonvolatile memory to calibrate and temperature compensate a family of automotive pressure sensor modules for a wide range of applications. A specially developed digital communications interface permits calibration of a sensor module using the existing module connector pins after the module has been fully assembled and encapsulated. This approach eliminates any post-trim processing that could affect the sensor calibration. Module customization and calibration can be performed as an integral part of the end-of-line testing that is done at the completion of the sensor module manufacturing flow. Sub-micron CMOS circuit fabrication, bulk silicon micromachining, and wafer level bonding technology are uniquely combined to produce a cost-effective part which meets relevant automotive pressure sensor performance and durability criteria. Both digital and analog sensor outputs are available. This fully digital signal processing circuit provides programmable customer features and a significant degree of application flexibility without the system overhead and cost associated with a microprocessor implementation. It also provides a signal conditioning platform that can be applied to a variety of sensing technologies beyond just silicon piezoresistive pressure sensors.