Ambient-light sensor ups battery life -

Ambient-light sensor ups battery life


Capella Microsystems announced the Filtron family that detects the amount of ambient light surrounding notebooks computers and mobile handsets, and adjusts the brightness of the LCD to provide an almost perfect match to the needs of the human eye. By providing such a close match, the device eliminates excessive backlighting and increases system battery life. Note that backlighting typically consumes a considerable portion of the overall battery power.

According to the company, the devices can increase handset battery life by up to 100%. They also reduce eye strain due to the close match of the brightness requirements of the human eye, and because of a built-in digital filter that removes flicker from ambient florescent lights. The matching comes thanks to a proprietary optical filter technology that only detects wavelengths in the range of 450 to 650 nm. This technology, manufactured with a semiconductor process, eliminates the extra step of placing a plastic filter over the photo diode.

The low-pass filter that removes florescent light flicker is implemented with a digital filter which eliminates a bulky analog filter capacitor. The light to be sensed travels through a hole in the chip package and illuminates the die. The light passes through the top layers of the die which consists of the Filtron notch filter that only passes the narrow frequency range. The filtered light then falls on a photo diode which sends its signal through the digital filter and into the 9-bit digital-to-analog converter.

The CM3200HS operates with ambient light ranges from 0.5 to 350 Lux, and the CM3200 operates in ranges of 10 to 10,000 Lux. The CM3000 uses an external resistor to set the threshold of an internal comparator that produces an on or off output for the desired ambient light range. Both parts are now in production, housed in CMPs (clean mold compound packages) that measures 3 by 4 mm, and OPLGA packages that measure 1.8 by 2.35 by 1 mm. In lots of 1000, they sell for $.60 each. More information is available at

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