A CMOS Time-of-Flight Image Sensor with High Dynamic Range Digital Pixel

Abstract

To widen measuring range and suppress background light, a CMOS time-of-flight image sensor with high dynamic range digital pixel is proposed. The sensing charge is quantized by extended-counting analogue-to-digital converter (ADC) which consists of pixel coarse quantization and column fine quantization. To maximize dynamic range in limited pixel area, the coarse quantization circuit is shared by 2×2 pixels, in which a novel up/down counter with a small number of transistors is proposed. Based on the pixel circuit, a 32×32 prototype TOF imager with 12μm-pitch digital pixel is designed in 0.11μm 1P4M CMOS image sensor technology. Simulation results show that a 104.6dB dynamic range of this ADC for wide measuring range is achieved at a frame rate of 50Hz.