Crosstalk? No Problem! Combined proximity and ambient light sensor for straightforward and flexible design

A new hybrid sensor of OSRAM Opto Semiconductors eases the installation of proximity and ambient light sensor technology in smartphones and similar devices. The sensor combines emitter and detector and it is designed to eliminate crosstalk in many applications. Suppressing this effect normally requires large efforts. For the first time, designers are also able to adapt the sensitivity of the ambient light sensor to the transparency of various smartphone covers.

The digital sensor SFH 7773 detects objects up to a distance of 15 cm and simultaneously measures the intensity of the ambient light. Its black 5.3 x 2.5 x 1.2 mm large package is hardly noticed behind transparent covers of smartphones. Thanks to highly efficient chip technologies its power consumption is low – a maximum of 5 µA flows in stand-by mode, 300 µA in operation – and therefore it is ideally suited for portable devices.

Design prevents Reflections
Proximity sensors detect objects by receiving the reflection of an emitted light signal. But the cover of a smartphone, for example, also reflects light back to the sensor. This so-called crosstalk usually is intercepted by installing an optical barrier. Alternatively the emitter is placed at a distance which prevents the cover reflections to reach the detector. However, both alternatives are rather complex. OSRAM now developed the SFH 7773 so that designers do not have to worry about crosstalk anymore: inside the device, emitter and detector chip are located sufficiently far apart from each other. Additionally, apertures are integrated in the package which prevent crosstalk or significantly reduce it.

User-definable sensitivity
To a large extend the user is free to select the integration time of the detector and thus the detection range of the proximity sensor via the I2C interface. That way also the ambient light sensor can be adjusted to the transparency of the smartphone cover. A variety of sensitivity levels is available, ranging from 3 to approximately 65,500 lux and 0.03 to 655 lux. “This means that now for the first time our customers can optimize the device for their respective application – from the operating distance to the sensitivity of the ambient light sensor”, Bianka Schnabel points out. She is responsible for OSRAM Opto Semiconductors’ product marketing of the sensor. “Due to this considerably simplified design work and flexibility of use, combined ambient light and proximity functions become more attractive for the middle segment of portable devices.”
 
For more information on the use of SFH 7773 and the topic of crosstalk, please refer to application note http://www.osram-os.com/Appnote_SFH_7773.

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