A high dynamic range SPAD pixel for time of flight imaging

Direct time of flight (TOF) pixels implemented with single photon avalanche diodes (SPADs) are the most suitable candidates for high sensitivity and picosecond timing resolution TOF sensors. However, their performance is severely limited in high dynamic range (HDR) applications such as advanced driver assistance systems (ADAS) and gesture recognition. Sampling the full dynamic range of the SPAD detector requires high bit-depth counters which until now has resulted in large pixel area and low fill-factor (FF). We present a SPAD-based tOf pixel in 40nm CMOS achieving the highest dynamic range over the state of the art. Dual time-gate sampling with two in-pixel 14-bit ripple counters achieves a counter-limited dynamic range of 84dB. The dynamic range of the pixel can be further extended by chaining the counters sampling with one time-gate to reach the intrinsic SPAD dynamic range limit of 119dB in a single exposure. The pixel has a 40pm × 20pm pitch and 16% FF. It generates 7 selectable sub-nanosecond time-gates down to 330ps with differential nonlinearity (DNL) smaller than 1 % of the time-gate width and a total temporal range tunable between 1.65ns to 40ns.