Image Sensor Dark Current Compensation via Dual Sub-Array Segmentation
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Solution Overview
Problem
In image sensor arrays, the increase in pixel density leads to smaller pixel sizes, resulting in reduced signal-to-noise ratio due to proportional dark current levels, and variations in signal processing channels cause inaccuracies in low-light conditions.
Innovation Solution
A method involving a dual sub-array image sensor system where one sub-array measures dark current signals while the other captures images, allowing for location-based dark current compensation and channel difference calibration to adjust image signals accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of pixels in an image sensor array is increased to achieve higher resolution, then the resolution is improved, but the size of individual pixels must be reduced which results in decreased signal-to-noise ratio
Solution Approach 1:
The image sensor array is divided into multiple processing channels (e.g., red, green, blue color channels), and dark current compensation is performed separately for each channel. This segmentation allows targeted compensation for channel-specific variations, improving overall image quality while maintaining high pixel density
Solution Approach 2:
The patent applies location-based dark current compensation where compensation values are adjusted according to pixel position within the sensor array. This parameter change approach accounts for spatial variations in dark current characteristics, effectively improving signal-to-noise ratio without requiring larger pixel sizes
2Area of stationary object
If the size of individual pixels is reduced to keep the die size small, then the die size is controlled, but the signal-to-noise ratio decreases due to reduced photogenerated charge
Solution Approach 1:
Location-based compensation values are calculated and applied to each pixel based on its position in the array. This allows the system to maintain small pixel sizes while compensating for the reduced signal level through software-based correction, effectively improving signal-to-noise ratio without increasing physical pixel area
Solution Approach 2:
A dark current reference array is used to create a model of dark current characteristics that is then copied and applied to compensate the main image sensor array. This allows accurate dark current subtraction from the captured images, improving signal-to-noise ratio while maintaining compact pixel design
3Adaptability or versatility
If different processing channels are used for different color bands, then color image capture capability is improved, but channel variations due to processing differences and temperature cause measurement inaccuracies
Solution Approach 1:
The patent implements separate dark current compensation for each processing channel (red, green, blue) based on location-based measurements. This channel-specific segmentation allows the system to account for and correct inter-channel variations, maintaining accurate color capture while compensating for processing differences and temperature effects
Solution Approach 2:
The system uses a dark current reference array to continuously monitor and measure dark current characteristics across all channels. This feedback mechanism allows real-time adjustment of compensation values for each channel, correcting for variations caused by processing differences and temperature changes, thereby improving measurement precision
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 approach enhances image clarity in low-light conditions by accurately compensating for dark current and channel variations, improving the signal-to-noise ratio without increasing chip size or cost.
Implementation Method 1
The leakage current in the pixel is often referred to as the dark current of the device, i.e., the current through the light sensitive element in the absence of any light
Implementation Method 2
Each pixel in an image sensor array converts the light incident on that pixel into electronic charge
Data Source
AI summary
A method for compensating for dark current in an image sensor array. In a representative embodiments, the method includes determining a nominal average dark current for the image sensor array, determining location of each pixel in the image sensor array, obtaining a nominal dark current associated with each pixel based on the nominal average dark current and on the location of the pixel, and subtracting the associated nominal dark current from the image signal for each pixel. At least two of the pixels have differing associated nominal dark currents. In other representative embodiments compensation values for dark currents and for differences in channel processing are determined during the same time period.