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Open AccessArticle

A Highly Linear CMOS Image Sensor Design Based on an Adaptive Nonlinear Ramp Generator and Fully Differential Pipeline Sampling Quantization with a Double Auto-Zeroing Technique

1
Xi’an Microelectronic Technology Institute, No. 198 Taibai South Road, Yanta District, Xi’an 710071, China
2
School of Microelectronics, Xi dian University, No. 2 Taibai South Road, Yanta District, Xi’an 710071, China
3
Department of Electronic Engineering, Xi’an University of Technology, No. 5, Jinhua South Road, Beilin District, Xi’an 710054, China
*
Author to whom correspondence should be addressed.
Sensors 2020, 20(4), 1046; https://doi.org/10.3390/s20041046
Received: 28 January 2020 / Revised: 12 February 2020 / Accepted: 12 February 2020 / Published: 14 February 2020
(This article belongs to the Special Issue Electronics for Sensors)
For a complementary metal-oxide-semiconductor image sensor with highly linear, low noise and high frame rate, the nonlinear correction and frame rate improvement techniques are becoming very important. The in-pixel source follower transistor and the integration capacitor on the floating diffusion node cause linearity degradation. In order to address this problem, this paper proposes an adaptive nonlinear ramp generator circuit based on dummy pixels used in single-slope analog-to-digital converter topology for a complementary metal-oxide-semiconductor (CMOS) image sensor. In the proposed approach, the traditional linear ramp generator circuit is replaced with the new proposed adaptive nonlinear ramp generator circuit that can mitigate the nonlinearity of the pixel unit circuit, especially the gain nonlinearity of the source follower transistor and the integration capacitor nonlinearity of the floating diffusion node. Moreover, in order to enhance the frame rate and address the issue of high column fixed pattern noise, a new readout scheme of fully differential pipeline sampling quantization with a double auto-zeroing technique is proposed. Compared with the conventional readout structure without a fully differential pipeline sampling quantization technique and double auto-zeroing technique, the proposed readout scheme cannot only enhance the frame rate but can also improve the consistency of the offset and delay information of different column comparators and significantly reduce the column fixed pattern noise. The proposed techniques are simulated and verified with a prototype chip fabricated using typical 180 nm CMOS process technology. The obtained measurement results demonstrate that the overall nonlinearity of the CMOS image sensor is reduced from 1.03% to 0.047%, the efficiency of the comparator is improved from 85.3% to 100%, and the column fixed pattern noise is reduced from 0.43% to 0.019%. View Full-Text
Keywords: CMOS image sensor; linearity; adaptive nonlinear ramp; fully differential pipeline; double auto-zeroing; high framerate; fixed pattern noise; floating diffusion; readout scheme; ramp generator circuit CMOS image sensor; linearity; adaptive nonlinear ramp; fully differential pipeline; double auto-zeroing; high framerate; fixed pattern noise; floating diffusion; readout scheme; ramp generator circuit
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Li, C.; Han, B.; He, J.; Guo, Z.; Wu, L. A Highly Linear CMOS Image Sensor Design Based on an Adaptive Nonlinear Ramp Generator and Fully Differential Pipeline Sampling Quantization with a Double Auto-Zeroing Technique. Sensors 2020, 20, 1046.

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