Using an infrared laser, ST Microelectronics’ new proximity detector for mobile phones can measure distances to within a centimeter or two.
The component could enable future smartphones to repond to more sophisticated touchless commands, distinguishing between as many as eight simple hand gestures, said company representatives on the STMicro stand at Mobile World Congress.
Traditional proximity detectors contain a sensor that detects when a beam of infrared light from an adjacent LED is reflected off a nearby object. While the intensity of the reflected light can give some information about the proximity of the object, this can also be affected by the object’s color or surface finish. Typically, they are placed next to the phone’s earpiece or front-facing camera.
Software running on a demo phone showed a traditional detector responding strongly to objects within about 5 cm, but barely reacting beyond that. The same app also showed the new detector’s response varying proportionally with the distance to an obstacle, out to about 50 cm.
What is the air-speed velocity of an unladen photon?
The new detector is much more precise because it calculates the time of flight of individual photons emitted by an infrared laser and reflected back to a sensor consisting of a single-photon avalanche diode (SPAD), said STMicro representative Hervé Grotard. He declined to explain exactly how the component measures the flight time, saying only that it was done by performing statistical calculations on a number of results gathered over time. Its power consumption will be equivalent to that of existing, less precise components, he said.
His colleague Jocelyn Leheup demonstrated how the detector can distinguish between gestures. Moving a hand in close towards a demo phone’s screen and then briskly backing away again prompted an app to display a symbol representing a tap. Performing the same gesture twice in succession triggered the symbol for a double tap. Passing a hand from one side of the screen to the other, 10 or 20 cm in front of it, triggered a swipe symbol, while the same gesture from side to side and back was detected as a double swipe. The detector did not distinguish between left-to-right and right-to-left movements, however.
Leheup also showed how an app could distinguish between the broad obstacle of a swipe with all fingers extended, the narrow obstacle of a single finger extended, and the fluctuation in distance when two fingers extended in a V are swiped in front of the sensor. In all an app could distinguish between as many as eight gestures, he said.
Making things pretty
The new detector could even be used to help phone cameras autofocus in macro mode, suggested Leheup.
Grotard also pointed to the cosmetic advantages for phone manufacturers. Traditional detectors require two unsightly apertures in the front of the phone, one for light leaving the LED and the other for its return to the sensor. The infrared laser’s beam being much narrower, and the SPAD being more sensitive, the holes can be much smaller with the new detector, and the laser and sensor are small enough to be concealed behind the earphone grill if desired, he said.
Samples of the component are already available, and Grotard said he expects the first phones using it on the market in May.