A SPAD-Based Hybrid Time-of-Flight Image Sensor With PWM and Non-Linear Spatiotemporal Coincidence

This paper presents an image sensor system based on single-photon avalanche diode (SPAD) utilizing a hybrid time-of-flight (ToF) method, which achieves an imaging resolution of 64×128 based on a hybrid scanning system. The primary components of the image sensor system include a 16 × 8 SPADs array fabricated using 130nm CMOS technology, along with 128 passive quenching circuits and 128 pulse shaping circuits within the pixels, a digital signal processing (DSP) circuit implemented on the FPGA, and a laser driving circuit with adjustable pulse width. The laser pulse width can be adaptively modified according to the bin size of the partial histogram, thereby improving the signal-to-background light ratio (SBR) and reducing measurement jitter. The DSP incorporates a hybrid partial histogram (HPH) algorithm based on both direct time-of-flight (DToF) and indirect time-of-flight (IToF), along with a non-linear spatiotemporal coincidence detection (NSCD) circuit. The proposed HPH algorithm significantly reduces the storage resource requirements for histograms, eliminating the need for in-pixel time-to-digital converter (TDC). Each pixel’s histogram requires only 180 bits of storage resource. Moreover, the IToF algorithm effectively enhances the system’s measurement precision. The NSCD significantly improves the sensor’s background noise suppression and weak echo detection capabilities. Experimental results indicate that, under a background light intensity of 60 Klux, the image sensor can measure distances up to 60 m, with a measurement precision less than 1 cm.