A Six-Tap iToF Imager with Wide Signal Intensity Range Using Linearization of Linear-Logarithmic Response.

Area of Science:

• Optoelectronics
• Computer Vision
• Sensor Technology

Background:

• Time-of-flight (ToF) image sensors require a broad dynamic range to capture varying light intensities, from diffuse to retroreflective signals.
• Existing linear-logarithmic (Lin-Log) pixel responses in indirect ToF (iToF) sensors face challenges in maintaining linearity across this wide span.

Purpose of the Study:

• To develop and validate a signal-intensity range-extension technique for short-pulse multi-tap indirect ToF sensors.
• To linearize the Lin-Log pixel response for improved accuracy and robustness in diverse lighting conditions.

Main Methods:

• Derivation of per-pixel two-region (2R) and three-region (3R) models covering linear, transition, and logarithmic response regimes.
• Application of these models to recover a near-linear signal from iToF sensor data.
• Experimental validation using a six-tap iToF imager with varying target distances and reflectivities.

Main Results:

• The three-region (3R) linearization method significantly improves linearity near the transition point compared to two-region approaches.
• Pixel-wise 3R linearization yields accurate and stable depth imaging results, reducing average error and pixel-wise deviations.
• Range measurements achieved centimeter-level resolution over distances from 1.8 to 13.0 m, reducing the linearity-error bound from ±6.7%FS to ±1.5%FS.

Conclusions:

• Lin-Log pixels combined with pixel-wise three-region linearization enable robust ToF sensing over an extended dynamic range.
• This technique is suitable for practical environments with large reflectance variations, enhancing the reliability of depth imaging applications.
• Further improvements can address residual periodic deviations attributed to minor pulse-width mismatches.