A Time-to-Amplitude Converter With High Impedance Switch Topology for Single-Photon Time-of-Flight Measurement

Zhong Wu,Yue Xu,Zhiqiang Ma

doi:10.1109/access.2021.3053758

Abstract

This paper presents a novel time-to-amplitude converter (TAC) for single-photon direct time-of-flight (d-TOF) measurement. An innovative high impedance switch approach is proposed to significantly improve the stability of the integral current and to increase the swing of the timing voltage, enabling high linearity together with low power consumption on TAC. Implemented in a standard $0.18~\mu \text{m}$ CMOS technology, the TAC occupies only an area of $100~\mu \text{m}^{2}$ , featuring a compact configuration. The experimental results indicate that the presented TAC can acquire a 78 ps timing resolution in a 20 ns full-scale range (FSR) under the supply of 1.8 V. In particular, the TAC gains an excellent linearity characteristic with the very low differential nonlinearity (DNL) and integral nonlinearity (INL) within ±0.1 LSB and ±0.15 LSB, respectively. Additionally, the extremely low dynamic power consumption of $20~\mu \text{W}$ and the high pixel fill factor of 16 % are also achieved simultaneously. Thanks to the outstanding advantages of high-performance and compactness, the proposed TAC may be a promising candidate to realize high-density compact TOF-based imagers.

Highlights

Owing to low manufacturing cost, low power consumption, easiness of integration, and mass-production capability, single-photon avalanche diode (SPAD) detectors fabricated in standard CMOS technology have been receiving great attention in various application areas, such as light detection and ranging (LiDAR), fluorescence lifetime imaging microscopy (FLIM), Raman spectroscopy, three-dimensional (3D) imaging, and deep learning aided signal detection [1]–[4]
After it was bonded and mounted on a custom printed circuit board (PCB), the to-amplitude converter (TAC) was measured by using an off-chip analog-to-digital converter (ADC) to quantize the readout voltage
Considering the large load capacitance of the PAD and PCB, the TAC is followed by an on-chip voltage follower to enhance the circuit driving capacity for the measurements

Summary

INTRODUCTION

Owing to low manufacturing cost, low power consumption, easiness of integration, and mass-production capability, single-photon avalanche diode (SPAD) detectors fabricated in standard CMOS technology have been receiving great attention in various application areas, such as light detection and ranging (LiDAR), fluorescence lifetime imaging microscopy (FLIM), Raman spectroscopy, three-dimensional (3D) imaging, and deep learning aided signal detection [1]–[4]. 1-ps single-shot precision is achieved for a wide-range TDC by applying a fundamental method of counting the full clock cycles and a single-stage interpolating method simultaneously [14] These presented TDC architectures are too complex to be suitable for high-density d-TOF pixel integration. Z. Wu et al.: TAC With High Impedance Switch Topology for Single-Photon Time-of-Flight Measurement in one-column or half-column largely reduce the area occupation and remarkably enhance the pixel fill factor [15], it seriously limits the frame rate of imaging and increases the complexity of the pixel interface circuits. We propose a compact TAC structure with high impedance switch topology to solve these problems in the conventional TACs. A stable integral current source with a high impedance switch is employed to enable the accurate time-amplitude conversion.

TAC STRUCTURE AND OPERATING PRINCIPLE

EXPERIMENTAL RESULTS AND DISCUSSIONS

CONCLUSION