1D ToF sensor delivers higher performance

By Alex Pluemer, contributing writer

ams claims the smallest integrated, 1D time-of-flight (ToF) distance measurement and proximity sensing module on the market. The new TMF8701 sensor is designed to trigger facial recognition systems on smartphones when the user’s face comes within range of the phone’s display.

The TMF8701 triggers a smartphone’s facial recognition system when an object comes within 60 cm of the device’s display screen. The sensor is “always on” but draws only 940 µA in proximity sensing mode when sampling at 10 Hz, placing very little demand on the phone’s battery.

The TMF8701 also differentiates between the reflection of a human face beyond the device’s display cover glass and the reflection of a fingerprint or other smudge on the display itself, a common problem with ToF sensors. The sensor turns off the facial recognition system and activates the display when objects (such as the user’s fingers) come within 0–10 cm of the device’s screen. The accurate distance measurements that the TMF8701 provides also support the laser-detect auto-focus function on smartphones’ selfie cameras, particularly in poorly lit environments.

The TMF8701, housed in a 2.2 × 3.6 × 1.0-mm package, fits in a narrow bezel, making it suited for devices that feature a high display-screen-to-body ratio. The sensor features a Class 1 Eye safe vertical-cavity surface emitting laser (VCSEL) infrared emitter that isn’t negatively affected by interference from ambient light and delivers accurate distance measurements in a range of lighting conditions. Under normal lighting conditions, the module is ±5% accurate at distances between 20 and 60 cm and maintains that accuracy in bright sunlight (100 klux) at up to 35 cm.

The module incorporates multiple single photon avalanche photodiode (SPAD) light detectors, a time-to-digital converter, and a histogram processing core for on-chip implementation of all histogram-based presence detection, distance measurement, and proximity-sensing algorithms.

The TMF8701 is in mass production and is priced at $2.60 in quantities of 5,000 units. An evaluation kit for the TMF8701 is also available. For more information, visit ams.com/TMF8701 .