An in-pixel histogramming TDC based on octonary search and 4-tap phase
detection for SPAD-based flash LiDAR Sensor
Abstract
This paper presents an in-pixel histogramming time-to-digital converter
(hTDC) based on octonary search and 4-tap phase detection, aiming to
improve frame rate and reduce distance error. The proposed hTDC is a
12-bit two-step converter consisting of a 6-bit coarse quantization and
a 6-bit fine quantization, which achieves a time resolution of 120 ps
without a GHz reference frequency and supports multiphoton counting up
to 2 GHz. The proposed hTDC is designed in 0.11 μm CMOS process with an
area consumption of 6900 μm 2. Timestamp sequences
from a behavioral-level model are imported to the hTDC circuit for
simulation verification. The post-simulation results show that the
proposed hTDC achieves about 0.8% depth precision in 9-m range for
short-range system design specifications and about 0.2% depth precision
in 48-m range for long-range system design specifications. Under 30 klux
background light conditions, the proposed hTDC can be used for
SPAD-based flash LiDAR sensor to achieve a frame rate to 40 fps with
200-ps resolution in 9-m range.