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SENSOR BUSINESS, MARKETING, AND TECHNOLOGY DEVELOPMENTS: PHILIPS DRIVES OPPORTUNITIES FOR AMR SENSORS.(Philips Semiconductors (Eindhoven, Netherlands))

Article Excerpt
Anisotropic magnetoresistive (AMR) sensors, which use thin-film permalloy (nickel-iron) resistors whose resistance changes in the presence of an external magnetic field, offer key benefits for speed and position/angle measurement applications.

In contrast to the typical variable reluctance (VR) sensor, the AMR sensor is capable of providing a zero-speed signal, which can be advantageous in applications requiring detection of very low speeds, such as car navigation or automatic brake assistance. Unlike the VR sensor, the output signal of the AMR sensor does not vary with rotation speed. Since the strength of its output signal is independent of the frequency of the target's rotation, the AMR sensor can be cost-effectively interfaced to a control unit.

The VR sensor, moreover, has key drawbacks for use in crankshaft position/angle sensing for ignition timing (the moment at which to fire a spark in each cylinder). The VR sensor cannot sense the position of the crankshaft before the starter motor has made the crankshaft rotate a certain speed, creating a delay at start-up. Considerable processing of the VR sensor's signal is required to obtain a reasonable switch point accuracy because the amplitude and frequency output of the VR pick up coil depend on the shaft's angular velocity. Since engine misfire must be detected at any time during operation, it is beneficial to use a crankshaft sensor that can detect very small variations in the crankshaft's angular velocity. Camshaft sensors function similarly to crankshaft sensors.

The AMR sensor provides a larger output signal than the Hall effect sensor, contributing to a superior signal-to-noise ratio and higher immunity to electromagnetic interference. The higher sensitivity and output signal of the AMR sensor allows for a larger air gap between the AMR sensor and the magnet/target at comparable target field strength. In addition, unlike the Hall effect sensor, the AMR sensor can be easily designed to measure strong or weak (low) magnetic fields. AMR sensors can allow for a simpler mechanical set-up in a complete system than a Hall effect sensor, and AMR sensors can use ferrite magnets rather than more expensive samarium cobalt magnets.

Philips Semiconductors (Eindhoven, The Netherlands)(www.semiconductors.philips.com), a division of Royal Philips Electronics (NYSE: PHG, AEX: PHI), has been at the forefront of spearheading market opportunities for its anisotropic magnetoresistive rotational speed, angle sensors, and low-field sensors, as well as for its silicon temperature sensors.

Philips Semiconductors' offers a variety of rotational speed sensors that are capable of detecting down to zero speed for such applications as automotive anti-lock braking systems (ABS), gearbox control, or camshaft and crankshaft sensing. Their rotational speed sensors can operate with passive or active targets, and are available in a multi-chip package containing the sensor and the signal conditioning IC to streamline the design-in process. Philips Semiconductors can also provide a modular two-package rotational speed sensor combined with a signal conditioning IC. The rotational speed sensors can be set-up using a ferromagnetic target.

Guenter Reiniger, marketing manager for sensor products, noted that the main application for Philips Semiconductors' rotational speed sensors is ABS for passenger cars. Indicative of their clout in the automotive anisopropic...

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