UV-A light detection for wearable and mobile devices

27 October 2021 Opto-Electronics

Monitoring vital signs such as pulse or oxygen saturation in the blood via smartphones and smartwatches has been available for several years. The corresponding UV channel of the TSL2585 from ams Osram detects the amount of UV-A radiation in natural sunlight, enabling the user to be warned of excessive UV-A radiation. Thanks to its extremely compact dimensions, the sensor is ideally suited for space-constrained wearable and other mobile applications.

While the UV-C portion of sunlight is blocked by the earth’s atmosphere, UV-A and UV-B radiation reaches the Earth’s surface. UV-B radiation penetrates only the upper layers of the skin and is responsible for sunburn. UV-A radiation, which accounts for around 90% of the UV component that reaches the Earth’s surface, penetrates much deeper into the lower layers of the skin and can, in some cases, have significant health consequences – from weakening the connective tissue to faster ageing of the skin and a higher probability to develop skin cancer. With the help of this new ambient light sensor, smartwatch users can now be warned as soon as the UV-A dose in their environment becomes too high.

The sensor utilises advanced interference filters which are precisely deposited on each photodiode pixel to create a 315-400 nm UV-A channel, a human-eye response photopic channel and an IR channel. These provide essential information for indoor/outdoor identification, UV index calculation and ambient illuminance detection. Additionally, the TSL2585’s unique edge-located photodiode placement supports very narrow µBezel design.

The TSL2585 has integrated light flicker detection on-chip and is equipped with three modulators with up to 14 kHz sampling rate. By providing the illuminance information and ambient light flicker information to the phone camera, it supports fast auto exposure and removal of banding effects caused by flicker from environmental lighting.

The compact dimensions of the extremely flat package – only 2,0 mm x 1,0 mm x 0,35 mm – allow for space-saving system designs to help manufacturers of extremely compact devices. The sensor can be operated with a voltage of 1,8 V and consumes only 0,7 µA when inactive.


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