Time-to-Digital Converter for Low-Power Direct Time-of-Flight System

Master thesis (2022)

Authors

G. Xu Electrical Engineering, Mathematics and Computer Science

Contributors

S. Du Electronic Instrumentation - EEMCS (supervisor 1)
S. Nihtianova Electronic Instrumentation - EEMCS (supervisor 2)
C. Gao Electronics - EEMCS (supervisor 2)
Faculty
Electrical Engineering, Mathematics and Computer Science
Copyright: © 2022 Guo Xu
Low power Chopping DToF Ring-based TDC Small DNL Double sampling
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Published Date

29-09-2022

Language

English

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Faculty

Electrical Engineering, Mathematics and Computer Science

Abstract

Depth sensing technology has developed rapidly recently due to its broad applications. Time-of-Flight (ToF) is a popular technology in depth sensing because of its advantages in high measuring accuracy and low complexity in image processing. ToF technologies are divided into two kinds: indirect time-of-flight (iToF) and direct Time-of-Flight (dToF). Compared to the iToF, dToF can detect targets at a longer distance by directly calculating the flight time of the laser. To obtain time information, the dToF system requires a Time-to-Digital Converter (TDC). This thesis proposes a system-level model to optimize the TDC parameters for a dToF system used in an autofocus system of a mobile phone. According to the simulation result of the system modeling, a ring-based TDC is chosen and built using a shared and duty-cycled Voltage-Controlled Oscillator (VCO). To decrease the DNL of the TDC, chopping comparators are used in this design. In addition, to save power and area, a new method called double sampling is used to align the coarse and fine phases of the ring based TDC. The proposed TDC achieves a resolution of 100 ps and a DNL of −0.27/+0.37 and an average power of 0.179 mW/TDC, which are smaller than that of state-of-the-art TDCs used in dToF systems. SMIC 55BSC technology is used to design and tape out the TDC.