A 50-ps Gated VCRO-Based TDC With Compact Phase Interpolators for Flash LiDAR

This article describes a small footprint, low power gated voltage-controlled ring oscillator (VCRO)-based Time-To-Digital converter (TDC) for Flash Light Detection and Ranging (LiDAR) applications. A group of compact local phase interpolators (PIs) are used to improve the resolution, which is highly area-saving and compatible with in-pixel TDC structure. A non-reset operation mode is introduced to increase the linearity by taking advantage of the dynamic element matching (DEM) property. The proposed TDC has been fabricated in a 0.18-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> HV-CMOS technology in a 32 <inline-formula> <tex-math notation="LaTeX">$\times32$ </tex-math></inline-formula> array, achieving a resolution of 50 ps. A Phase Lock Loop (PLL) is adopted to track the process, voltage, and temperature (PVT) variations and make the resolution tunable. A power-saving analog buffer is used to distribute the stable control voltage to all the in-pixel TDCs. Measurements show a good linearity performance and array uniformity (a deviation of only 0.89 ps), making it suitable for Flash LiDAR applications.