A Time-of-Flight Image Sensor Using 8-Tap P-N Junction Demodulator Pixels

Area of Science:

• Optoelectronics
• Image Sensing Technology
• Computer Vision

Background:

• Traditional time-of-flight (ToF) sensors struggle with ambient light interference and motion artifacts.
• Existing hybrid-type ToF sensors have limitations in range and linearity, especially under challenging lighting conditions.

Purpose of the Study:

• To develop and demonstrate a novel 8-Tap P-N junction demodulator (PND) pixel for hybrid-type short-pulse (SP)-based ToF measurements.
• To achieve long-range (>10 m) ToF measurements under strong ambient light using single-frame signals.
• To improve depth precision, linearity, and ambient-light canceling capabilities of ToF sensors.

Main Methods:

• Implementation of an 8-tap PND pixel array (120x60) using 0.11 µm CIS technology.
• Utilizing eight consecutive time-gating windows with a 10 ns gating width for demodulation.
• Development and application of an improved depth-adaptive time-gating-number assignment (DATA) technique and a nonlinearity error correction technique.

Main Results:

• Demonstrated the first single-frame, long-range (>10 m) ToF measurements under high ambient light (80 klux).
• Achieved a depth precision of 16.4 cm (1.4% of max range) and a maximum non-linearity error of 0.6% over a 1.0-11.5 m range.
• Exhibited 2.5 times better depth linearity compared to state-of-the-art 4-tap hybrid-type ToF sensors.

Conclusions:

• The 8-tap PND ToF image sensor enables motion-artifact-free, long-range depth measurements in challenging ambient light conditions.
• The developed DATA technique and nonlinearity correction significantly enhance the performance and extend the depth range of ToF systems.
• This technology represents a significant advancement for applications requiring accurate depth sensing in bright environments.