Industry’s first digital ultraviolet index sensors

10th February 2014
Nat Bowers

Silicon Labs has announced what the company claim is the industry’s first single-chip digital ultraviolet (UV) index sensor ICs. The Si1132 and Si114x sensors are designed to track UV sun exposure, heart/pulse rate and blood oximetry and provide proximity/gesture control for smartphone and wearable computing products.

The latest additions to Silicon Labs’ optical sensor family, these ICs suit activity-tracking wrist and arm bands, smart watches and smartphone handsets. They also provide ambient light and infrared (IR) proximity sensing capabilities for health and fitness applications. The Si1132 UV index and ambient light sensor utilises an industry-standard I2C interface to read digital UV index values; while the Si1145/46/47 UV and IR proximity/ambient light sensors provide a choice of one, two or three integrated LED drivers with 15 selectable drive levels for gesture detection. While conventional UV sensors combine UV-sensitive photodiodes with an external MCU, ADC and signal processing firmware, Silicon Labs is the first to combine all of this functionality into a single-chip solution. Supplied in an exceptionally small 2x2mm package, the Si1132 and Si114x sensor ICs help reduce the design’s footprint and bill of material cost.

When combined with an accelerometer, the sensors enable the implementation of sleep tracking in wearable applications. They also offer enhanced control of LCD backlighting in mixed-light source environments. Since they can measure both infrared and visible light levels, this yields a cost-effective and functional means of adjusting backlighting to ease eyestrain and reduce power without distracting the end user. Offering excellent performance under light sources including direct sunlight, the bust sensing architecture also includes an ambient light sensor capable of sensing light levels up to 128kLux. Excellent immunity to artificial light flicker noise and natural light flutter noise is provided by the photodiode response and associated digital conversion circuitry.

With average current as low as 1.2µA for once-per-second UV measurements, the sensors feature an ultra-low-power architecture which enables thinner wearable designs with smaller batteries as well as extending battery life. The UV index sensors also offer high IR sensor sensitivity through the use of a single 25.6µs IR-LED on-time. This provides significantly longer battery life in motion sensing/gesture applications and enables a sensing range up to 50cm. Additionally, power consumption is reduced via the dynamic adjustment of LED currents.

The Si114x sensors incorporate LED drivers which enable the implementation of reflective heart rate and blood oximetry measurement capabilities for health and fitness trackers. They also enable advanced motion sensing, gesture sensing and touchless interfaces that support end-user control from a distance. The Si1146 enables motion sensing and touchless control in the z- and x-axis, with the Si1147 adding a third for 3D motion sensing. Both provide reflectance measurements that can be post-processed to determine gestures.

Mark Thompson, Vice President and General Manager, Access, Power and Sensor products, Silicon Labs, comments: “Wearable designs require highly integrated, small-footprint and low-power sensing solutions, and we’re meeting this need with the industry’s first single-chip digital UV index sensors that also provide ambient light and IR sensing capabilities for innovative health and fitness applications. Silicon Labs is the only UV index sensor vendor that offers a broad portfolio of energy-friendly MCUs, wireless MCUs and transceivers, and an array of other sensors that can be combined into system solutions for the fast-growing wearables market.”

Supplied in a 10-pin 2x2mm QFN package, Silicon Labs’ Si1132 and Si114x UV sensors are available now for sampling and in volume production. The Si1132 sensor is priced at $1.10 (USD) in 10,000 unit quantities; while the Si114x sensors are priced from $1.32 (USD) in 10,000 unit quantities. Silicon Labs also offers the UVIrSlider2EK evaluation kit for $50.00 (USD).

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