CMOS Image Sensor Column Readout Circuit Switching
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Solution Overview
Problem
Conventional image sensors face limitations in achieving high frame rates due to throughput constraints in the column bus and signal readout circuits, leading to reduced light sensitivity and increased manufacturing costs, as well as crosstalk artifacts from capacitive coupling between parallel column lines.
Innovation Solution
The integration of a switching device that alternates the connection of column lines between precharge and readout circuits, allowing for simultaneous charging and discharging of one line while reading out another, reduces the number of required column readout circuits and minimizes crosstalk by arranging lines closer together without additional shielding, thus enhancing frame rate and light sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple parallel column lines are used to increase throughput rate, then frame rate is improved, but crosstalk between lines increases due to capacitive coupling
Solution Approach 1:
The patent implements periodic switching between precharge and readout operations on alternating column lines. During each time period, odd column lines perform precharge while even column lines perform readout, then they switch roles in the next period. This periodic alternation ensures that adjacent lines are never simultaneously active, eliminating capacitive coupling interference while maintaining high throughput through parallel processing across multiple lines over time.
2Area of stationary object
If column lines are arranged closer together to reduce space requirements, then chip area is reduced, but crosstalk between lines increases
Solution Approach 1:
By implementing periodic switching where adjacent column lines alternate between precharge and readout operations, the patent eliminates simultaneous signal activity on neighboring lines. This temporal separation allows the lines to be positioned closer together without incurring crosstalk penalties, as the capacitive coupling only matters when both lines are actively switching or holding signals simultaneously.
3Productivity
If more column readout circuits are provided to handle more column lines, then throughput rate is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent makes each column readout circuit universal by enabling it to serve multiple column lines through time-multiplexed operation. A single readout circuit can sequentially or alternatively service multiple column lines depending on which lines are currently in readout mode versus precharge mode. This multi-functionality reduces the total number of readout circuits needed while maintaining the ability to process signals from all column lines, thereby reducing device complexity and cost while preserving throughput capability.
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 solution enables higher frame rates with reduced crosstalk and light sensitivity loss, while also decreasing the surface requirements for column readout circuits, thereby lowering manufacturing costs and improving chip yield.
Implementation Method 1
crosstalk artifacts from capacitive coupling between parallel column lines
Data Source
AI summary
An image sensor, in particular a CMOS image sensor, for electronic cameras includes a plurality of light-sensitive pixels arranged in rows and columns for generating exposure-dependent pixel signals. A plurality of column lines, at least one precharge circuit for charging or discharging the column lines and at least one column readout circuit for reading out the pixel signals of the respective column are associated with a respective column. The image sensor has at least one switching device which is adapted to couple, in a first switch state, one of the column lines of a respective column to the precharge circuit and another one of the column lines of the respective column to the column readout circuit.