High-Linearity High-Resolution Time-of-Flight Linear-Array Digital Image Sensor Using Time-Domain Feedback

Abstract

This paper presents a high-linearity high-resolution time-of-flight (ToF) linear-array digital image sensor using a time-domain negative feedback technique. A coarse ToF measurement loop uses a 5-bit digital-to-time converter (DTC) and a delayed gating-pulse generator for time-domain feedback to find the zero of the difference between ToF and the digital estimate of the gating-pulse delay while maintaining a constant operating point of the analog readout circuits. A fine ToF measurement uses a delta-sigma modulation (DSM) loop using the time-domain feedback with a bit-stream signal form. Because of the self-contained property of the DSM for low distortion and noise exploited by the oversampling signal processing, the proposed technique provides high-linearity and high-range resolution in the fine ToF measurement. A prototype ToF sensor of 16.8 × 16.8 μm2 two-tap pixels and fabricated in a 0.11 μm (1P4M) CMOS image sensors (CIS) process achieves +0.9%/−0.47% maximum nonlinearity error and a resolution of 0.24 mm (median) for the measurement range of 0–1.05 m. The ToF sensor produces an 11-bit fully digital output with a ToF measurement time of 22.4 ms.

Characteristics of Distance Errors of Infrared Sensor Relation to Colour Surfaces

“…Nonlinearities cause significant variance in the measured values, limiting thus the sensor applicability in a given setting to its full extent without error compensation. When considering the linear characteristic of IR ToF sensor (Kim et al, 2021) and the occurrence of nonlinearities, it is possible to measure the distance only in a certain (linear) range, otherwise, it is necessary to compensate for errors. Various alternative methods working on different principles can be used to identify and describe the nonlinear dependence of distance error values of sensor (Zhang et al, 2020;Ma and Liu, 2018).…”