Proximity Sensors Deliver Unmatched Range, Sensitivity, and Power Efficiency

With the pressure to deliver consumer devices that are more user friendly, as well as aware of their environments, designers are seeking more features and higher performance from human interface (HI) technology. Hence, achieving advanced motion and gesture control in these products has been challenging. With the result, tradeoffs created between battery life/power efficiency and performance often compromise end-user experience. Keeping these issues in mind, analog and mixed-signal ICs supplier Silicon Labs has readied a new generation of proximity sensors for HI applications.

These novel multi-LED infrared (IR) units, labeled Si114x, combine advances in HI technology with robust IR sensing architecture to deliver the industry’s most power-efficient proximity sensors that brag highest sensitivity and longest-range from a tiny footprint. The Si114x sensors come in miniature, optically clear 2- x 2- x 0.75-mm 10-pin QFN packages. In fact, Silicon Labs’ latest proximity sensors with ambient light capability are the newest addition to QuickSense family, which was introduced about 15 months ago.

The supplier claims that the multi-LED Si114x sensors offer industry’s highest-sensitivity and longest-range proximity sensing with lowest power consumption. The sensor’s ultra-sensitive photodiodes enable over 50cm proximity range for a one-dimensional system or up to 15 cm for a multi-dimensional system. While the unit’s robust IR sensing architecture permits the on-board ambient light sensor to sense light levels up to 128 klux, the rated system power consumption is also minimized by minimizing the on-time of power-hungry IR LEDs. Thus, using 25.6µs pulses for proximity measurements, the system power consumption is kept below 1mA even with three on-chip LED drivers. Likewise, in power-down mode, the current consumption is less than 20nA and standby current is rated at 500nA.

Since a proximity sensor’s detection range and sensitivity is determined by the system’s signal-to-noise ratio (SNR), higher SNR achieves longer range. Now, numerous variables contribute to a system’s SNR performance. These variables include ambient noise/light compensation, photo-diode sensitivity, filtering, and analog-to-digital converter (ADC) architecture. While competing solutions may address one or two of these variables, the patent-pending Si114x architecture addresses all of these parameters to minimize noise and maximize performance, said Ahsan Javed, Silicon Labs’ marketing manager for HI products. He added, “The combined architectural optimizations result in very high system SNR, enabling the Si114x proximity sensors to achieve the industry’s longest range, highest sensitivity, and fastest data acquisition speed.”

Since the sensor is a reflectance-based unit, the SNR is expressed as minimum reflectance sensitivity in the data sheet, which for the Si114x sensors is < < 1μW/cm².

To give designers the flexibility of implementing a one-dimensional HI system or multi-dimensional solution, the Si114x family offers sensor options with up to three on-chip IR LED drivers. The one-dimensional HI system offers a detection range of more than 50cm, while multi-dimensional systems are capable of gesture sensing up to 15cm.

In short, the Si114x family offers one-, two- and three-axis sensing capabilities, depending on the number of LED drivers on-chip. All the three members, Si1141/42/43 , feature selectable drive levels and integrated high-sensitivity photodiode, digital converter, digital signal processor (DSP) and I²C digital interface to offer excellent performance under a wide dynamic range of light sources including direct sunlight. The photodiode response and associated digital conversion circuitry provide excellent immunity to artificial light flicker noise. Housed in a 10-lead 2mm x 2mm QFN package, the proximity sensors can operate from 1.8V to 3.6V over a wide operating temperature range of –40 to 85°C.

In this design, the Si114x sensors measure ambient light and proximity of an expected object through an IR reflectivity system. Here, an IR light is emitted from an LED, which bounces off an object and is sensed by an optical sensor. Using this technique, Si1141 with single LED driver is capable of supporting proximity motion detection. And Si1142 with two IR LED drivers facilitates z- and x-axis motion sensing for touchless slider interfaces. Likewise, Si1143 with three IR LED drivers enables innovative 3D motion and gesture sensing for the ultimate in multi-dimensional touchless control.

To enable myriad motion and gesture detection and expected-object distance correction in applications such as handsets, eReaders, netbooks, tablets, personal media players, toys, office equipment, industrial controls, security systems, point-of-sale stations, and many other products, the Si114x sensors are tailored to work with capacitive touch-sense microcontrollers like F700, F800, or F99x MCUs. In such schemes, the Si114x devices’ sensing modes provide valuable information to the MCU to determine the background light type, such as sunlight, fluorescent or incandescent. And, then use it to improve IR proximity sensing, optimize infrared sensing power, enhance backlight dimming functions in a display, or control other devices within the system.

Like all members of the QuickSense portfolio, the Si114x family is supported by the QuickSense Studio, a user-friendly, easy-to-use software development environment that enables developers to program, debug and analyze proximity, ambient light, and capacitive-touch sensing applications. It streamlines the configuration of infrared proximity and ambient light sensors through a library of application programming interfaces (APIs). The graphical environment offers the ability to generate C code for proximity and motion detection, gesture detection, and algorithmic identification of background light types.

Complete evaluation and development kits, including the IRSLIDER2EK evaluation kit for Si1142-based touchless sliders and the Si1140DK development kit for Si1143 3-LED evaluation, are available on DigiKey's website.

To evaluate power consumption levels required for proximity and ambient-light sensing applications, the supplier offers an online optical sensor current estimator utility. It is available at www.silabs.com/sensor-current-estimator.