CMOS Image Sensor Column-Line Voltage Equalization for CDS Accuracy
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Solution Overview
Problem
Existing image sensors face challenges in maintaining accurate pixel output levels across column lines due to varying voltage levels when select transistors are turned off, leading to decreased accuracy in correlated double sampling and dynamic range.
Innovation Solution
The image sensor employs a pixel array and line disconnection circuit to adjust voltage levels of column lines to a desired level, ensuring uniformity before select transistors are turned on, using control signals from a row driver and timing controller to manage the pixel output levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If select transistors are turned off to read pixel signals, then pixel signal output is enabled, but column lines have varying voltage levels causing decreased measurement precision
Solution Approach 1:
The patent applies preliminary action by adjusting the voltage levels of column lines to a desired uniform level before the select transistors are turned on for signal reading. This pre-adjustment ensures that all column lines start at the same voltage potential, preventing the voltage variations that would otherwise degrade correlated double sampling accuracy during the readout phase.
2Ease of operation
If different row addresses are used for pixel groups, then pixel identification is enabled, but address determination complexity increases
Solution Approach 1:
The patent segments the pixel array into multiple pixel groups, where each pixel group contains pixels from different rows that share the same column line. This segmentation allows the system to treat each pixel group as a unified unit for voltage adjustment purposes, simplifying the addressing scheme by using a single row address per pixel group rather than requiring separate addressing for each individual row within the group.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach prevents column lines from having different voltages when select transistors are off, enhancing the accuracy of correlated double sampling and maintaining a stable dynamic range, thereby improving image sensor performance.
Implementation Method 1
The CMOS image sensor includes pixels composed of CMOS transistors and converts light energy into an electrical signal by using a photoelectric conversion element (or device) included in each pixel.
Data Source
AI summary
An image sensor includes a pixel array that includes a first pixel group located in a first row and including a first select transistor and a first floating diffusion region, a second pixel group located in a second row and including a second select transistor and a second floating diffusion region, and a column line connected to both the first pixel group and the second pixel group. While charges generated by a photoelectric conversion element of the first pixel group are transferred to the first floating diffusion region, the first select transistor is turned off, the second select transistor is turned on, and a first voltage is applied to the column line through the second select transistor. A photoelectric conversion element of the second pixel group generates charges prior to the photoelectric conversion element of the first pixel group, so as to be transferred to the second floating diffusion region.