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SENSOR MARKETS AND TECHNOLOGIES UPDATE: MOTOROLA SPD STREAMLINES TIRE PRESSURE SENSING AND MONITORING.

Article Excerpt
Capitalizing on expanding opportunities for direct tire pressure monitoring systems, which have key advantages over the indirect approach, Motorola Sensor Products Division (Tempe, AZ, 480-413-3333)(www.motorola.com/semiconductor) has introduced an integrated tire pressure sensor, and also offers a chipset enabling a tire pressure monitoring system that integrates with existing remote keyless entry (RKE) systems.

Motorola's new MPXY8020A monolithic tire pressure sensor includes a surface micromachined silicon capacitive pressure sensing element, a PTC (positive temperature coefficient) resistor for temperature sensing, and an interface circuit with a wake-up feature on a single chip. The chip is housed in a compact, media-isolated super small outline package (SSOP), which provides an effective package for use in tire pressure monitoring remote sensing modules mounted on the tire's valve stem or wheel well. The sensor is available in a tape and reel format for mass production. The MPXY8020A has a pressure range of up to 637.5 kPa, a pressure sensing accuracy of +/- 7.5 kPa, a temperature range of -40 degrees C to +125 degrees C, a temperature sensor accuracy of +/- 4 degrees C at 25 degrees C, and a 2.1-3.6 V operating range.

Jeff Burgess, a new product development engineer at Motorola SPD, told SBD that the MPXY8020A is the first capacitive sensing device for tire pressure sensing with a digital output for pressure and temperature. He noted that the surface micromachined silicon capacitive pressure sensor consumes less die space and less power than a bulk micromachined silicon piezoresistive pressure sensor. Although Motorola did provide a silicon variable capacitive manifold absolute pressure (SCAP) sensor many years ago, the company's mass-produced pressure sensors (including those for MAP/BAP (manifold absolute pressure/barometric absolute pressure) sensing) have used piezoresistive sensing technology.

Whereas the silicon micromachined piezoresistive pressure sensor uses piezoresistors and a bulk micromachined diaphragm, the variable capacitance silicon micromachined pressure sensor, which detects the change in capacitance between a fixed plate and a moveable diaphragm, uses surface micromachining to create a vacuum cavity and the polysilicon top capacitor plate.

The size benefit of the capacitive sensor allowed Motorola to integrate the sensor and signal conditioning electronics on the same silicon die, thereby creating an integrated device with greater functionality that is less expensive to produce. To achieve more cost-effective manufacturing of the new capacitive tire pressure sensor, Motorola SPD integrated their silicon micromachining process into their existing, standard CMOS process for producing electronic circuitry.

The MPXY8020A is compatible with tire pressure monitoring systems that use remote RF (radio frequency) communications, and it is designed to readily integrate into RKE systems. The pressure sensor, the heart of the tire pressure monitoring system, measures a tire's inflation level. When used in a...

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