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Optoelectronics/Displays  

Light sensors detect behind translucent materials

Posted: 18 Mar 2010     Print Version  Bookmark and Share

Keywords:light sensor  touchscreen  consumer electronics  LED 

TSL2771 light sensor

Texas Advanced Optoelectronic Solutions Inc. (TAOS) has launched the first members of its next generation digital ambient light sensor (ALS) and proximity detection family specifically designed to operate behind darkened glass or other translucent materials.

The TSL2771 device family provides both ambient light sensing and proximity detection in a single device that consumes far less power than currently available comparable solutions and is designed to eliminate the need to use clear glass/plastic in front of the sensor or drill holes/slots into the display, bezel or frame.

Proximity detection is suited for touchscreen smart phones to automatically turn off the display or control other user functions and can also be used in laptops, desktop computers and monitors to conserve energy or maintain information privacy when the user is not present. Other emerging applications for proximity sensing technology include touchless display controls activation and management as well as human gesture detection.

"The need for ambient light sensors to operate behind darkened glass or other translucent materials has emerged as a critical requirement in today's consumer electronic products," said Carlo Strippoli, TAOS VP of sales and marketing. "Consumers have become increasingly sophisticated and manufacturers need a way to be able to deliver sleeker, more compelling designs while still being able to deliver the benefits of improved picture quality and reduced energy consumption that digital ambient light sensors provide. Our next generation of high sensitivity digital ambient light and proximity devices delivers in both areas to help consumer electronics manufacturers design more appealing 'green' products."

The TSL2771 ALS and proximity detection device family incorporates an IR LED current-limited driver, ADC, interrupt capability, multiple I²C interface voltage options and flexible programming allowing it to be configured into many different applications. As darkened glass or translucent materials can be transparent to IR wavelengths while attenuating visible light by 100x or more, the device utilises TAOS' patented dual-photodiode architecture that allows the sensor system to compensate for the increased IR component. When combined with the ability to adjust the analogue gain settings up to 128x, the device excels in challenging low-light level applications.

"Power consumption is another key advantage to the TSL2771 device family," said Kerry Glover, TAOS applications manager. "In many of the portable applications, battery life is very critical. Traditional proximity detection methods require a significant amount of power. With the new TAOS architecture, as few as one IR pulse is required for presence detection. This can provide 10x in power savings over traditional analogue or other digital solutions."

In applications requiring longer distance detection, an external driver can be utilised to boost the power such that a person can be detected in front of a monitor. A unique state machine allows the device to go into a lower power wait state, thereby only having the high power external detection running a very small portion of the time. For applications requiring only ambient light sensing, the next generation of TAOS devices also includes the TSL2580/81 high-sensitivity ALS. To accelerate time-to-market and reduce design-in effort, TAOS provides support for software device drivers and/or C-reference code as well as evaluation modules.

The TSL27711 (3V bus) and TSL27713 (1.8V bus) are packaged in DFN packages. Pricing for both the TSL27711 and TSL27713 is Rs.49.41 ($1.07) in quantities of 1,000 pieces. The TSL2580 with SMBus interface and the TSL2581 with I²C interface are available in FN packages and are priced at Rs.34.63 ($0.75) each in quantities of 1,000 pieces.





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