Image Sensor Voltage Drop Correction Line for FPN Reduction
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Solution Overview
Problem
In-pixel correlated double sampling (CDS) in image sensors results in residual fixed pattern noise (FPN) due to voltage drops across column lines, affecting signal quality and requiring post-processing correction, which is critical for high-speed and large-array image sensors.
Innovation Solution
An image sensor design incorporating a voltage drop correction line that extends along the column of pixels, providing a correction voltage signal to compensate for voltage drops, thereby reducing FPN and improving dynamic range by adding the correction voltage to the CDS signal during read-out.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If in-pixel CDS is used to achieve high-speed readout, then readout speed is improved, but residual FPN remains due to voltage drops across column lines
Solution Approach 1:
A correction voltage line is introduced as an intermediary element to compensate for voltage drops in the column lines. This separate correction path allows the pixel signal to be adjusted without affecting the primary readout speed, thereby eliminating residual FPN while maintaining high-speed operation.
Solution Approach 2:
The invention changes the voltage parameter by introducing a correction voltage that dynamically compensates for the voltage drops occurring in the column lines. This parameter adjustment occurs in the analog domain before digital conversion, improving signal quality without impacting readout speed.
2Measurement precision
If column line resistance is reduced to minimize voltage drop, then FPN is reduced, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The voltage compensation function is segmented from the primary column line by creating a separate correction voltage line. This segmentation allows the original column line to maintain its simple structure for high-speed signal transmission, while the correction line handles the FPN compensation independently, avoiding increased manufacturing complexity.
3Productivity
If in-pixel CDS is implemented instead of column-level CDS, then readout speed is improved, but FPN removal capability is reduced
Solution Approach 1:
The invention merges the benefits of both in-pixel CDS and column-level CDS by combining the fast in-pixel sampling with an additional correction voltage line that provides column-level FPN removal. This hybrid approach achieves high readout speed while effectively eliminating residual FPN that would otherwise remain with in-pixel CDS alone.
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
The solution effectively reduces FPN and eliminates the need for post-processing corrections, enhancing the dynamic range and signal quality of image sensors by compensating for voltage drops across column lines, particularly beneficial for high-speed and large-array sensors.
Implementation Method 1
there will be a voltage drop affecting the pixel signal received by the column line and the voltage drop is varying in dependence of a position of the pixel in the column
Data Source
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AI summary
An image sensor (100), comprises: an array of pixels (110) for detecting light incident on the pixel, wherein each pixel (110) in the array comprises a photodetector (112) and an in-pixel correlated double sampling, CDS, circuitry (114) to output a CDS signal representative of a difference between a photointegrated signal and a reset signal; a column line (130), which extends along and is associated with a column of pixels (110) in the array; a voltage drop correction line (134), which extends along and is associated with the column of pixels (110), wherein the voltage drop correction line (134) is configured to provide a correction voltage signal to a pixel (110) such that the correction voltage signal is added to the CDS signal for forming the pixel signal received by the column line (130) and corrects for voltage drop of the pixel signal in read-out through the column line (130).