Lock-in Pixel Based Time-of-Flight Range Imagers: An Overview

Abstract

Time-of-flight (TOF) range imaging is a promising technology for various applications such as touchless control, augmented reality interface, and automotive. The TOF range imagers are classified into two methods: direct TOF with single photo avalanche diodes and indirect TOF with lock-in pixels. The indirect TOF range imagers have advantages in terms of a high spatial resolution and high depth precision because their pixels are simple and can handle many photons at one time. This paper reviews and discusses principal lock-in pixels reported both in the past and present, including circuit-based and charge-modulator-based lock-in pixels. In addition, key technologies that include enhancing sensitivity and background suppression techniques are also discussed.

Snapshot super-resolution indirect time-of-flight camera using a grating-based subpixel encoder and depth-regularizing compressive reconstruction

“…The top row of Fig. 1 shows a schematic diagram of the conventional pulse iToF camera [9,10]. The camera emits a sequence of rectangular light pulses (red waveform in the figure) in the time domain, and a photodiode array receives reflected light that temporally encodes the scene depth.…”

An SOI-Based Lock-in Pixel with a Shallow Buried Channel for Reducing Parasitic Light Sensitivity and Improving Modulation Contrast

“…The TOF measurement is divided into two methods: direct TOF (dTOF) [3]- [8] and indirect TOF (iTOF) [9]- [21]. In the dTOF method, a single photon avalanche diode (SPAD) and a time digital converter are used to measure the TOF.…”

“…In contrast, the iTOF sensors utilize a lock-in pixel with a fast electronic shutter or time-gating, enabling time-dependent signal acquisition. The design of the lock-in pixel is critical in the iTOF sensors, and many pixel structures [21] have been presented to achieve high-speed modulation, high modulation contrast (MC), and high sensitivity. In the iTOF sensors, increasing the pixel counts is relatively Manuscript received November 11, 2022.…”