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Indirect time-of-fight sensor with in-pixel adaptable background light suppression based on delta-sigma technique

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Title
Indirect time-of-fight sensor with in-pixel adaptable background light suppression based on delta-sigma technique
Other Titles
델타-시그마 방식을 통하여 외광 세기에 따라 유동적으로 픽셀 내에서 외광 제거가 가능한 indirect ToF 센서
Author
Park, Dahwan
Advisor
Kim, Seong-Jin
Keywords
Time-of-Flight; 3D Image sensor; Pixel
Issue Date
2020-08
Publisher
Graduate School of UNIST
Abstract
Entering the era of the fourth industrial revolution (4IR), interest about camera is growing rapidly. The demand for detecting range has been increased by consumer of electronics applications such as gesture recognition like kinect gaming and robotic vision. The depth sensing technology can be classified into 2 types. One is sensing with optical sources and the other is sensing without optical sources. The most popular approaches include radar and time-of-flight (TOF) sensing systems. In the non-optical sensing category, the well-known radar range-finding system utilizes the radio waves to measure the range. Radar is the abbreviation of radio detection and ranging. Literally, this system uses radio wave for detecting the range and it consists of receiving part and transmitting part which produces electromagnetic waves. However, this systems is weak on spatial resolution. Because large array size receiver is hard to be materialized. Time-of-flight (ToF) principle is measuring distance based on time difference between emitted light wave and reflected light wave. ToF is classified 2 types; direct-ToF (dToF) and indirect-ToF (iToF). The direct-ToF is measurement of the time delay between emitted light and reflected light, while indirect-ToF is measurement of the phase delay of a periodic waveform. In direct ToF system, single-photon avalanche diode (SPAD) is the most commonly used sensing device because of high sensitivity and fast responsivity. In this research, the proposed sensor is implemented to iToF structure with depth calculation using phase shift. It has 4 advantages compared to previous ΔΣ based background light suppression i-ToF. As modulation frequency increases, switching noise becomes more dominant. Therefore, to reduce unnecessary switching noise, smart adaptable ΔΣ operation is proposed. Process variation is one of the factors causing depth error. To compensate process variation, in-pixel automatic chopping controller is proposed. Additionally, to increase background suppression capability, all pixel include individual integrator for global ΔΣ operation in pixel and pinned photodiode is implemented for high electron transfer speed. This chip is fabricated with a 0.11um DBH CIS process.
Description
Department of Electrical Engineering
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