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Ambient light sensor tunes LCD light to eye-friendly level

Posted: 23 Aug 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Capella Microsystems? Filtron? ambient light sensors?

Capella's ambient light sensor

Capella Microsystems Inc. said its Filtron family of ambient light sensors eliminates excessive backlighting in portable products including notebook computers, cellphones, DVD players, PDAs, MP3 players, iPods and GPS, thereby preserving battery life in these devices. These chips detect the amount of ambient light in the environment and adjust the LCD brightness accordingly to virtually match the requirements of the human eye, said the company.

The CM3200HS (high sensitivity), CM3200 and CM3000 devices integrate an optical filter, photo diode, digital filter and 9bit D/A converter that produces an analog output that varies linearly as the ambient light. The CM3200HS operates with ambient light ranges from 0.5 lux to 350 lux, and the CM3200 operates in ranges of 10 lux 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, said the company. Power consumption is typically 80?A and less than 1nA with a shutdown feature. Voltage operation is 2.7-5.5V.

Capella Microsystems said backlighting typically consumes more battery power than any other function, and the new CM3200HS, CM3200 and CM3000 devices can increase the battery life of notebook computers by up to 41 percent and increase the battery life of cell phones by up to 100 percent. In addition to finding homes in portable products, the Filtron devices are also used to control screen brightness in plasma and LCD television screens and automobile dashboards.

The chips also reduce eye strain because they closely match the brightness requirements of the human eye, and a built-in digital filter removes flicker from ambient florescent lights. The company touts the devices are the industry's best at emulating the human eye thanks to a proprietary optical filter technology called Filtron that only detects wavelengths in the range of 450nm to 650nm. In addition, the optical filter technology is said to be the first made with a semiconductor process that eliminates the extra step of placing a plastic filter over the photodiode.

The chips are made with mixed-signal technology and contain approximately 7,000 transistors. Four applied patents for the technology are used in the new devices. The devices have a typical photodiode output variation of 0.04 percent per degree over the operating temperature range of -25C to 85C.

The CM3200HS and CM3200 devices are available in a Clean Mold Compound (CMP) package that measures 3-by-4mm, and an OPLGA package that measures 1.8-by-2.35-by-1mm. Both are priced at 60 cents in a CMP package in quantities of 1,000. Also available in CMP and OPLGA packages, the CM3000 is priced at 55 cents in a CMP package in quantities of 1,000.

- Gina Roos
eeProductCenter




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