Analogue, Mixed Signal, LSI


Time-of-flight proximity sensor

30 January 2019 Analogue, Mixed Signal, LSI

ams has introduced a 1D time-of-flight distance measurement and proximity sensing module that is ideal for implementing presence detection, for example to trigger the operation of a facial recognition system when the user’s face is in range.

Supplied in a 2,2 x 3,6 x 1,0 mm package, the TMF8701 integrates a VCSEL infrared emitter, multiple SPAD (single photon avalanche photodiode) light detectors, time-to-digital converter, and a histogram processing core. The device implements all histogram-based presence detection, distance measurement and proximity sensing algorithms on-chip.

The TMF8701 separately identifies reflections from fingerprint smudge contaminations on the display screen and optical reflections from objects beyond the cover glass, such as the user’s face, maintaining reliable performance even when the sensor’s aperture is dirty.

The Class 1 Eye Safe VCSEL emitter has enhanced immunity to interference from ambient light and produces accurate distance measurement in all lighting conditions: the module achieves accuracy of ±5% when measuring distance in the 20-60 cm range in normal lighting conditions. Even in bright sunlight (100 klux), ±5% accuracy is maintained at a range of up to 35 cm.

The low-power operation of the TMF8701 – it draws only 940 μA in proximity sensing mode when sampling at 10 Hz – makes it the ideal companion to a smartphone’s face recognition system. Always on, it triggers the higher-power face recognition system to start up when the time-of-flight sensor detects the presence of an object up to 60 cm from the display screen.

The proximity sensing capability of the device can also be used to trigger the display and face recognition system to switch off when detecting a reflective surface at a distance of 0-10 cm from the screen. The accuracy of the TMF8701’s distance measurements also supports the selfie camera’s LDAF (laser detect auto-focus) function, especially in low-light conditions.

For more information contact Marian Ledgerwood, Future Electronics, +27 21 421 8292, marian.ledgerwood@futureelectronics.com, www.futureelectronics.com



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