A CMOS time of flight (TOF) depth image sensor with in-pixel background cancellation and sensitivity improvement using phase shifting readout technique

Abstract

This paper presents a CMOS time-of-flight (TOF) image sensor with in-pixel background light cancellation for outdoor depth imaging application. The using of P+/N_well diode with proposed polarity switching integration and phase-shift readout (PSR) technique achieves the in-pixel background cancellation capability and sensitivity improvement. Moreover, the PSR also suppresses the column fixed-pattern-noise (FPN) without need of extra frame capturing. A prototype TOF sensing chip with a 64×64 array has been fabricated in TSMC standard 0.18pm CMOS process and verified. The pixel pitch is 20pmx20pm with a fill-factor of 33%. The achieved depth measurement range is 0.75 to 7.5 meters with a linearity error below 1.1%. The measured relative precision is 4.2% at a 7.5-meter target distance; and the background light suppression capability is up to 180k lux without saturation.