Abstract
An 8-tap CMOS lock-in pixel image sensor that has seven carrier-capturing and a draining time window was developed for short-pulse time-of-flight (TOF) measurements. The proposed pixel for the short-pulse TOF measurements has seven consecutive time-gating windows, each of which has the width of 6 ns, which is advantageous for high-resolution range imaging, particularly for relatively longer distances (>5 m) and under high ambient light operations. In order to enhance the depth resolution, a technique for the depth-adaptive time-gating-number assignment (DATA) for the short-pulse TOF measurement is proposed. A prototype of the 8-tap CMOS lock-in pixel image sensor is implemented with a 1POLY 4METAL 0.11-μm CIS process. The maximum non-linearity error of 1.56%FS for the range of 1–6.4 m and the depth resolution of 6.4 mm was obtained at 6.2 m using the DATA technique.
Highlights
Indirect time-of-flight (TOF) range image sensors are increasingly demanded for various application areas
In the Short-pulse time-of-flight (SP-TOF) method, the depth resolution is improved by making the gating-time width shorter, and the distance is extended by increasing the number of signal taps of the pixel and by using range-shifting techniques [14,15,16]
For the outdoor use of TOF sensors, the SP-TOF method is more advantageous because a lower amount of ambient light charge is accumulated by using a small-duty, energy-concentrated light pulse and the short gating-time window of the pixel
Summary
Indirect time-of-flight (TOF) range image sensors are increasingly demanded for various application areas. The present paper reports a new SP-TOF measurement technique using the 8-tap lock-in pixels and the depth-adaptive time-gating-number assignment (DATA) technique is used, where the number of gating times for the 7-tap outputs are adaptively changed to the distance by considering the dependency of the attenuated reflected light to the distance. Having this technique exploit the feature of flexible programming of gating pulse patterns in SP-TOF method is very effective for obtaining relatively high depth resolution for the entire measurement range by assigning larger gating numbers at farther regions, while suppressing the saturation of signals in the nearest regions by assigning fewer gating numbers.
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