An Indirect Time-of-Flight SPAD Pixel with Dynamic Comparator re-use for a Single-Slope ADC

This paper presents a 2-bin SPAD-based indirect time-of-flight (ITOF) pixel circuit with low power low-voltage differential clock distribution and a partially in-pixel single-slope ADC. An in-pixel dynamic comparator performs dual functions as a SPAD event-driven low-swing clock sampler and a comparator for self-referenced ADC conversion with digital delta reset sampling (DRS). The pixel achieves a full well capacity of 128 – 512 photons (6.83 – 8.82 effective bit depth), a low dynamic power consumption of 13.9-24.5 nW/MHz SPAD rate at a pitch of 7.2 μm in STMicroelectronics’ 40nm CMOS and is 3D stacking ready.