Hybrid Time-of-Flight Image Sensors for Middle-Range Outdoor Applications

Abstract

This paper introduces a new series of time-of-flight (TOF) range image sensors that can be used for outdoor middlerange (10m to 100m) applications by employing a small duty-cycle modulated light pulse with a relatively high optical peak power. This set of TOF sensors is referred to here as a hybrid TOF (hTOF) image sensor. The hTOF image sensor is based on the indirect TOF measurement principle but simultaneously uses the direct TOF concept for coarse measurements. Compared to conventional indirect TOF image sensors for outdoor middlerange applications, the hTOF image sensor has a distinct advantage due to the reduction of capturing ambient light charge. To show the potential of the hTOF image sensor for outdoor middle-range operation, a model of estimating distance precision of hTOF image sensors is built and applied it by using possible sensor specifications to estimate the distance precision of the hTOF range camera in 10m, 20m and 40m measurements under the ambient-light condition of 100klux and its feasibility is discussed. In outdoor 10m-range measurements, the advantage of hTOF image sensors compared to the conventional indirect TOF image sensors is discussed by considering the amount of captured ambient-light charge in pixels.

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

“…3 (a)) Adding intermediate gates requires additional gate drivers and wires which is not a big issue. Figure 8 shows a timing diagram for the four-tap TOF measurement [29], [34] using the proposed modulator. Synchronized with the light source, the modulation gates (G 1 -G 4 ) and the intermediate gates (G C1 -G C4 ) turns on sequentially.…”

“…Figure 10 shows the estimated σ D calculated for the previous and the proposed pixel by Eqs. ( 5) to ( 9) [29], [34].…”

“…N a includes both N a and the background signal acquired when a modulation gate turns off. Unlike [34], a readout time is not taken into consideration in Eq. ( 8).…”

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

“…The SP-iToF image sensor using the single-frame ToF calculation technique is also good for the motion artifact mitigation [17,21]. To emphasize the advantage of the SP-based iToF image sensors in long-range ToF measurements, hybrid-type SP-iToF image sensors has been proposed [31]. In the hybrid-type SP-iToF image sensors, numerous consecutive time-gating windows prepared by multi-tap pixels or the combination of the multi-tap pixels and range-shifted subframes are used for long-range ToF measurements.…”