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Proximity, ambient light sensor comes in single chip

Posted: 07 May 2008 ?? ?Print Version ?Bookmark and Share

Keywords:proximity and ambient light sensor?

Capella Microsystems Inc. has unveiled the CM3612 device, which it claims is the industry's first proximity and ambient light sensor in a single chip. The CM3612 extends battery life in touch screen products such as iPhones and other portable products including cellphones, notebook computers and digital cameras.

The proximity function increases battery life by enabling portable products to automatically turn off their screens when not being viewed, and the ambient light sensor extends battery life by allowing the automatic adjustment of screen brightness to match external light conditions.

The proximity sensor can also be used to deactivate a touch screen phone so that it does not dial numbers when in contact with a user's head. The ambient light sensor also reduces eye strain by matching the screen brightness to the requirements of the human eye.

In addition to its infrared proximity sensor and ambient light sensor, the chip contains a digital low-pass filter that removes fluorescent light flicker, 12bit ADC, DSP, temperature compensation circuit, I?C interface, oscillator and driver for an IR emitter. Voltage operation is 2.6-3.7V, and the typical current consumption is 130?A.

Capella said its Filtron technology, which eliminates the need for external optical filters for both the proximity and ambient light sensors, makes it possible for the first time to combine the proximity and ambient light sensor functions in a single chip. The ambient light sensor uses the Filtron technology to mimic the brightness sensor of the human eye by only detecting wavelengths in the range of 450-650nm.

The CM3612 enables the ambient light value to be read from a 12bit register via an I?C interface. A lower cost version, the CM3601, eliminates the I?C interface and uses a DAC to output the ambient light value as an analog output signal. Both chips use an optical band-pass filter to pass only the green light band (450-650nm) to a sensitive photo diode. The diode current level is converted to digital by a 12bit ADC, which feeds a digital low-pass filter that remove fluorescent light flicker.

Both chips use the same proximity sensor circuitry, which provides ambient light cancellation and processes the signal through a DSP which can be controlled by the I?C interface in the case of the CM3612. The output from the DSP is a binary output indicating a target is in proximity of the chip or not in proximity.

Pricing: In quantities of 10,000, the CM3612 is priced at $1.50 in an optical land grid (OPLGA) package that measures 2.35 x 1.8 x 1 mm, and the CM3601 is priced at $1.20 in an OPLGA that measures 2.35mm x 1.8mm x 1mm. Devices are sampling now.

- Gina Roos

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