Journal of Sensor Science and Technology (센서학회지)

The Korean Sensors Society (한국센서학회)
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Extension of the Dynamic Range using the Switching Operation of In-Pixel Inverter in Complementary Metal Oxide Semiconductor Image Sensors

  • Seong, Donghyun (School of Electronics Engineering, Kyunpook National University) ;
  • Choi, Byoung-Soo (School of Electronics Engineering, Kyunpook National University) ;
  • Kim, Sang-Hwan (School of Electronics Engineering, Kyunpook National University) ;
  • Lee, Jimin (School of Electronics Engineering, Kyunpook National University) ;
  • Lee, Jewon (School of Electronics Engineering, Kyunpook National University) ;
  • Lee, Junwoo (School of Electronics Engineering, Kyunpook National University) ;
  • Shin, Jang-Kyoo (School of Electronics Engineering, Kyunpook National University)
  • Received : 2018.12.27
  • Accepted : 2019.01.18
  • Published : 2019.03.31
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Abstract

This paper proposes the extension of the dynamic range in complementary metal oxide semiconductor (CMOS) image sensors (CIS) using switching operation of in-pixel inverter. A CMOS inverter is integrated in each unit pixel of the proposed CIS for switching operations. The n+/p-substrate photodiode junction capacitances are added to each unit pixel. When the output voltage of the photodiode is less than half of the power supply voltage of the CMOS inverter, the output voltage of the CMOS inverter changes from 0 V to the power supply voltage. Hence, the output voltage of the CMOS inverter is adjusted by changing the supply voltage of the CMOS inverter. Thus, the switching point is adjusted according to light intensity when the supply voltage of the CMOS inverter changes. Switching operations are then performed because the CMOS inverter is integrated with in each unit pixel. The proposed CIS is composed of a pixel array, multiplexers, shift registers, and biasing circuits. The size of the proposed pixel is $10{\mu}m{\times}10{\mu}m$. The number of pixels is $150(H){\times}220(V)$. The proposed CIS was fabricated using a $0.18{\mu}m$ 1-poly 6-metal CMOS standard process and its characteristics were experimentally analyzed.

Keywords

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Fig. 1. Schematic diagram of the proposed unit pixel.

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Fig. 2. Cross-sectional view of the proposed unit pixel.

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Fig. 3. Timing diagram for the operation of the proposed method of dynamic range extension.

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Fig. 4. Comparison of pixel output voltage characteristics as a function of the light intensity between the conventional mode and the wide dynamic range mode.

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Fig. 5. Pixel output voltage characteristics according to power supply voltage of in-pixel CMOS inverter

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Fig. 6. Captured images when VREF is (a) 0 V, and (b) 3.3 V.

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Fig. 7. Simulation results of pixel output voltage characteristics according to the value of n+/p-sub junction capacitance.

Table 1. Characteristics of the proposed CMOS image sensor.

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