Bringing new functionality for controlling motion in portable electronic products requires low cost, low power consumption, unique functions and, of course, small size. Meet these criteria and applications proliferate. According to Marlene Bourne, principal analyst at Bourne Research, "The potential of triple-axis accelerometers is sparking the imagination of designers for all kinds of end uses, which will drive the growth of MEMS sensors in portable consumer electronics by nearly 10 percent over the next five years." Accelerometers are an integral part of features such as hand-motion based interfaces (think Apple iPhone) and provide movement, vibration, inclination and acceleration sensing including freefall detection. One of the bonus functions that acceleration sensing can provide to a portable product is managing the power consumption by turning the power on (or off) after the device has been touched or moved. These products target the same consumer applications in portable navigation devices, sports equipment and handheld devices.
Thinnest Digital Output Accelerometer
With a height of only 0.8 mm, Freescale Semiconductor claims its MMA7450L 3-axis digital-output accelerometer is the world's thinnest. Marlene Bourne of Bourne Research agrees. "Low profile is extremely important and Freescale has set the bar with one of the thinnest packages yet," she says. The 14-pin 3 × 5 × 0.8 mm plastic land grid array (LGA) package houses a 3-axis sensor that has two digital protocols, low power consumption and several features. The accelerometer can communicate on both I2C and SPI digital interface buses eliminating the need for a dedicated analog-to-digital converter. The unit has an operating current consumption of 400 µA that drops to 5 µA in the standby mode. Other features in the sensor include a threshold and pulse or click-detect for quick motion detection, offset calibration that eliminates the need for external memory and a g-select feature for choosing 2, 4 or 8g sensitivities.
http://rbi.ims.ca/5406-604
Thin Analog Output Accelerometer
Housed in a 5 × 3 × 0.9 mm Thin Land Grid Array (TLGA) 14-pin plastic package, STMicroelectronics analog-output LIS302ALK comes close to the thinnest 3-axis accelerometer. The LIS302ALK has a full-scale output of ±2g and is capable of measuring acceleration over a maximum bandwidth of 2.0 kHz. By using external capacitors, the device bandwidth can be reduced. The ratiometric output voltage unit typically consumes about 2 mW of power but in the power down mode the current consumption can be reduced to 1 µA. The design survives shock events up to 10,000g in 0.1 msec. While the LIS302ALK has an analog output, other products in the family, such as the LIS302DL, have an SPI and I2C digital interface.
http://rbi.ims.ca/5406-605
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