A CMOS Time-of-Flight Depth Image Sensor With In-Pixel Background Light Cancellation and Phase Shifting Readout Technique

Abstract

A CMOS time-of-flight (TOF) image sensor with in-pixel background light (BGL) cancellation and demodulation lock-in pixel is developed for both indoor and outdoor depth imaging applications. The proposed polarity switching integration technique using p+/n-well diode realizes the in-pixel BGL cancellation up to 180 klx. In addition, the developed phase-shift readout (PSR) effectively reduces the inherent correlated noise and column fixed-pattern noise (FPN) as well with sensitivity improvement. A prototyped pulse-modulation-based TOF sensing chip with a $64 \times 64$ pixel array, $20\mu \text {m} \times 20\mu \text{m}$ pixel pitch, and 33% fill factor has been fabricated in TSMC standard 0.18- $\mu \text{m}$ CMOS process and verified. The achieved depth sensing capability ranges from 0.75 to 7.5 m with a linearity error below 1.1%, and the measured relative precision is 4.2% at a 7.5-m target distance.