A 2-Tap Macro-Pixel-Based Indirect ToF CMOS Image Sensor for Multi-Frequency Demodulation

Indirect time of flight (IToF) allows for accurately retrieving 3D geometry without the need for exorbitant time resolution. Nevertheless, the use of continuous-wave (CW) periodic modulation brings the need for multiple frequency measurements to solve depth ambiguities or cope with multi-path interference. Sequential acquisition of multiple frames reduces the frame rate, while harmonic distortion of the modulation waveforms produces wiggling in the depth estimation. This paper presents and verifies the operation of an IToF CMOS image sensor designed to provide single-shot multi-frequency measurements. A macro-pixel structure allows acquiring multi-frame data in one shot, while resonant demodulation annihilates the harmonic content. The novel architecture consists of 10 μm ⇥ 10 μm 2-tap pixels with a 20% fill factor (FF). Post-layout simulations show promising 3D reconstruction for up to 16 different simultaneous frequencies.

keywords: ToF, CMOS imagers