A 32 × 32-Pixel Flash LiDAR Sensor With Noise Filtering for High-Background Noise Applications

Abstract

This article introduces a pulsed laser direct time-of-flight (dTOF) flash light detection and ranging (LiDAR) sensor fabricated in 0.18-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> HV CMOS technology. The chip includes <inline-formula> <tex-math notation="LaTeX">$32\times 32$ </tex-math></inline-formula> macro pixels and 1024 time-to-digital converters (TDCs). A noise filtering circuit with different threshold (<inline-formula> <tex-math notation="LaTeX">$\text{N}_{\mathrm {th}}$ </tex-math></inline-formula>) configuration is adopted in each macro pixel [formed by four single-photon avalanche diodes (SPADs)], which can suppress strong background light (BG) induced pile-up. To verify the imaging function and effectiveness of the noise filtering circuit, two systems are implemented (System1 for indoor imaging measurement and System2 for outdoor distance measurement). With the help of the noise filtering circuit and a reasonable signal-to-background noise ratio (SBR), the maximum detection range outdoors with reasonable accuracy can be greatly extended (from 12m &#x0040; N_th &#x003D; 1 of System2 to more than 20m &#x0040; N_th &#x003D; 2 of System2 under 70klux of background noise). The counter in the noise filtering circuit can be reused to get intensity information. A robust 13-bit TDC with a reliable reset is introduced. Thanks to a dedicated START/STOP logic and a Schmitt trigger, large TDC quantization errors can be avoided. It achieves a 200ps resolution (LSB) and exhibits an INL_p-p of 3.55LSB and a DNL_p-p of 0.53LSB. The maximum inter-frame rate can reach 270kfps with 16 IOs operating at speed of 500MHz. Combining 9k inter-frames to get one frame, a frame rate of 30 is achieved for an indoor 3-D imaging. For outdoor measurement, more laser pulses should be accumulated.