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Date: 30-04-13

Sensor for smartphone to prevent unwanted touch response

Osram Opto Semiconductors has launched a compact 4 x 2.1 x 1.35 mm measuring IR sensor for smartphones to prevents unintentional responses from the touch screen during telephone calls. The digital SFH 7776 sensor contains an infrared LED (IRED) and two detectors and performs two different functions. It registers the ambient brightness in order to control the display backlighting so that it can always be easily read but consumes as little power as possible. It also deactivates the touch function on the display as soon as you hold the phone up to your ear during a phone call. To do this the sensor emits infrared light that is reflected by approaching objects, such as your ear.

SFH 7776 is designed with high sensitivity of detection limit of 0.002 lux (lx) and does not need lenses to bundle the emitted infrared light. Measuring only 1.35 millimeters in height is nearly invisible by staying behind transparent phone covers. In standby mode this sensor consumes 0.8 micro Amperes of current.

“The SFH 777x series gives our customers a complete family of multifunctional sensors for an extremely wide range of phone covers”, said Dirk Sossenheimer, responsible for intelligent sensor applications at Osram Opto Semiconductors. What’s more, the SFH 7776 is designed so that the ambient light sensor doesn't react to short-term fluctuations in the brightness of various lamp types, caused for example by changes in the power supply frequency. This ensures that the display backlighting remains constant.

Crosstalk – an effect in which the emitted infrared light is reflected by the smartphone casing directly onto the receiver – is eliminated by the SFH 7776 in the component itself. Designers no longer need to provide separate optical barriers between the IRED and the detector, which makes it much easier to create robust, uncomplicated solutions for different setups.

Since the SFH 7776 covers the complete working range from 0 to 16 mm it would even react to direct contact (“zero distance detection”). The touch function of the display is therefore reliably deactivated even in marginal situations. “Overall, the SFH 7776 overcomes various challenges in terms of proximity and ambient light detection in the component itself, so designers can integrate the product in smartphones relatively easily”, added Dirk Sossenheimer.

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