Image Sensor Column Routing Wire Length Equalization
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Solution Overview
Problem
In image sensors, differences in wire lengths from the pixel array to the readout circuit cause variations in settling times, leading to fixed pattern noise due to differing capacitances and time constants among column routing wires.
Innovation Solution
The implementation of a spider routing structure with protrusion portions and partial wires in diagonal directions for column routing wires, ensuring that the sum of lengths of connection and protrusion portions of one wire equals the length of another, thereby minimizing capacitance differences and settling time deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional routing structures are used, then wiring layout is simple, but differences in wire lengths cause variations in settling times and capacitances
Solution Approach 1:
The column routing wire is divided into multiple segments: a first column routing wire with a first connection wiring portion and a protrusion portion, and a second column routing wire with a second connection wiring portion. This segmentation allows independent optimization of each segment's length to achieve uniform total lengths and minimize settling time variations.
Solution Approach 2:
The routing structure introduces asymmetric protrusion portions that extend in specific directions to compensate for length differences. The protrusion portions are strategically designed with different lengths and orientations to balance the total wire lengths from the pixel array to the readout circuit, creating an asymmetric layout that achieves symmetric performance in terms of settling time uniformity.
2Reliability
If wire lengths are equalized, then capacitance differences are reduced, but wiring structure becomes more complex
Solution Approach 1:
Different portions of the routing wires are designed with different local characteristics. The protrusion portions are locally added to specific wires to extend their lengths, while other wires maintain their original connection wiring portions. This local modification approach allows precise control of individual wire lengths to achieve uniform capacitance values without redesigning the entire routing structure.
Solution Approach 2:
The routing wires are extended not only in the column direction but also in diagonal directions through the protrusion portions. This multi-dimensional routing approach provides additional degrees of freedom for length adjustment, enabling equalization of wire lengths by utilizing spatial dimensions beyond the simple column-wise extension.
3Manufacturing precision
If protrusion portions are added to equalize wire lengths, then settling time deviation is minimized, but manufacturing complexity increases
Solution Approach 1:
The protrusion portions are pre-designed and pre-positioned in the routing structure during the layout phase. By calculating the required protrusion lengths in advance based on the pixel array and readout circuit positions, the manufacturing process is simplified as the protrusion portions can be directly fabricated without requiring complex post-processing or adjustment steps.
Data Source
AI summary
An image sensor includes: a pixel array outputting a pixel signal; and a column wiring unit including at least one first column routing wiring extending from the pixel array and including a first connection wiring portion and a protrusion and at least one second column routing wiring including a second connection wiring portion, wherein a sum of lengths of the at least one first connection wiring portion and the protrusion is substantially identical to a length of the at least one second connection wiring portion; and a readout circuit receiving the pixel signal from the column wiring unit.