CMOS Image Sensor Column-Line Precharge for Faster Readout
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Solution Overview
Problem
High frame rate operations in CMOS image sensors face challenges in reducing settling time for column data lines during correlated double sampling and analog-to-digital conversion, affecting the accuracy and dynamic range of image data.
Innovation Solution
The image sensor device employs a method where select transistors in different rows and columns are controlled to output pixel signals through specific column lines, with an IPF operation adjusting voltage levels of non-active column lines based on reset voltage levels from adjacent pixels, thereby minimizing settling time and ensuring consistent voltage levels across columns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of pixels is increased to improve resolution, then image quality is improved, but the time taken to read out data decreases
Solution Approach 1:
The pixel array is divided into multiple banks, with each bank having its own dedicated data line. This segmentation allows parallel readout operations across different banks, effectively reducing the overall data readout time while maintaining high pixel density and resolution.
2Productivity
If high frame rate operation is implemented to improve productivity, then data output speed is improved, but settling time of column data line becomes insufficient
Solution Approach 1:
The voltage stabilization operation is performed in advance during the period when the previous row's select transistor is still active. By preparing the column data line voltage before the next readout operation begins, the settling time requirement is eliminated, enabling high frame rate operation without compromising signal stability.
3Measurement precision
If settling time is extended to improve measurement precision, then data accuracy is improved, but the time available for high speed operation decreases
Solution Approach 1:
The voltage stabilization operation continues during the active period of the previous row's select transistor, overlapping with the ongoing readout operation. This continuous utilization of time resources allows voltage stabilization to occur without interrupting or extending the overall operation cycle, maintaining both accuracy and high speed operation.
Data Source
AI summary
An image sensor device includes a first pixel that is located at a first row and a first column and comprising a first select transistor and is configured to output a first pixel signal through a first column line, and a second pixel that is located at a second row different from the first row and the first column and comprising a second select transistor and is configured to output a second pixel signal through a second column line. During a first time period, the first select transistor is turned on and the first pixel signal is output, and during a second time period, the second select transistor is turned on, and a first voltage is applied to the second column line through the second select transistor, the second time period including the first time period.