Pulsed time-of-flight 3D-CMOS imaging using photogate-based active pixel sensors

A novel time-of-flight (ToF) 3D-image sensor based on photogate (PG) active pixel structures fabricated in a standard 0.35 mum CMOS process is presented. Distance measurements are performed using a pulsed near-infrared (lambda = 905 nm) laser with pulse widths of 30 ns to 60 ns for distance measurements up to 9 m. The developed ToF pixel consists of a photogate (A_PG = 30 x 30 mum²) and four floating diffusion (FD) readout nodes, which enable the detection of reflected laser pulse delay and efficient ambient light suppression. Our fabricated sensor contains 4 x 16 pixels and exhibits a dynamic range of 56 dB and a noise equivalent power of 4.46 W/m² using a single laser pulse.

I. Introduction

Nowadays, three different techniques for optical and contactless 3D distance measurements are well established: those based on interferometry, on triangulation, and on the time-of-flight (ToF) principle. Optical 3D image sensors can be found in many different applications, e.g. in the automotive industry or safety applications. Low-cost 3D image sensors based on standard CMOS technology can generate a huge market for these applications. In this work, we present a 3D image sensor using the time-of-flight principle, fabricated in a standard CMOS process.