A SPAD Based dToF Pixel with Log/Linear Multi-mode Operation for LiDAR Applications

In this paper, a novel pixel architecture with logarithmic and linear multi-mode distance calculation, is presented using a single photon avalanche diode (SPAD) for light detection and ranging (LiDAR) applications. The pixel gives an initial logarithmic response using a current starved pseudo-analog design, eventually switching to a linear response using a separate circuit with a highly stable current source. The logarithmic response is used to obtain a better resolution (post digitisation) for the smaller distances. While, the linear mode is configured for longer distances. Combination of the two modes results in a larger full scale range (FSR) with better resolution throughout the range. This approach reduces an unwanted high data-rate and requirement for a high resolution analog-to-digital converter (ADC). The proposed pixel is designed in standard CMOS 65 nm technology from TSMC. The pixel has a minimum detection distance of 2.34 cm (199.5 ps), a logarithmic depth resolution of 2.34 cm - 0.308 m and a linear depth resolution 0.59 m (3.9 ns). The dynamic range of the pixel is 500 m. The maximum voltage error of the logarithmic part is -1.86% to +0.5%.