Image Sensor Black Level Correction Using Shielded Pixels
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Solution Overview
Problem
The black level of an image sensor varies due to heat generated by signal processing circuits, which is difficult to compensate for and correct, especially in multi-layered semiconductor chips.
Innovation Solution
An image sensor with a pixel array, black level processing unit, and memory that calculates and applies a correction factor (Slope) based on light-shielded and imaging area outputs to adjust for temperature variations and heat distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If signal processing circuits are placed on the layer below the image sensor in a multi-layered structure, then integration density and device functionality are improved, but heat generation increases causing black level variation that is difficult to correct
Solution Approach 1:
The pixel array is divided into imaging areas and light-shielded areas, allowing separate measurement and correction of black level variations caused by heat from signal processing circuits. The light-shielded areas serve as reference regions to detect temperature-induced black level shifts independently from light signal variations.
Solution Approach 2:
The system dynamically adjusts the black level parameter based on detected temperature variations. By calculating the difference between black level values in light-shielded areas and reference values, the system computes a correction value that compensates for heat-induced black level shifts, thereby maintaining accurate black level despite temperature changes.
2Reliability
If black level correction is applied to compensate for heat variation, then image quality consistency is improved, but processing complexity and computational load increase
Solution Approach 1:
Reference black level values are pre-measured and stored for each pixel under known conditions. During imaging, these pre-stored reference values are compared with current black level measurements from light-shielded areas, allowing rapid correction without complex real-time calculations. The correction value is derived by simple subtraction and scaling operations.
Solution Approach 2:
The light-shielded areas serve as intermediary reference regions that isolate black level measurements from light signal interference. By using these intermediate measurement points, the system can detect temperature-induced black level variations without the complexity of analyzing full image data, simplifying the correction process.
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
Enables accurate black level correction across the image sensor, compensating for temperature and heat-related variations, ensuring consistent image quality.
Implementation Method 1
Signal processing circuits generate heat during their operation, and the amount of heat varies depending on the load on the signal processing circuits. The black level varies in accordance with heat
Data Source
AI summary
An image sensor includes a pixel array including at least one light-shielded area where no light enters and an imaging area where light enters, wherein each pixel includes a photoelectric conversion element, a black level processing unit that corrects an output of each pixel in the imaging area, and a memory that stores a predetermined black level reference for each pixel in the imaging area. The processing unit calculates a Slope, which is determined by an average output value at imaging of pixels in the at least one light-shielded area taken during imaging and a reference average output value of pixels in the at least one light-shielded area under certain conditions taken prior to imaging, and correct an output of each pixel in the imaging area using the predetermined black level reference and the Slope.