Global Shutter CMOS Image Sensor Light Noise Compensation
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Solution Overview
Problem
Global shutter CMOS image sensors experience image quality degradation due to light noise, such as leakage and dark currents, during the storage of accumulated charges in charge storage devices, leading to image distortion and quality issues.
Innovation Solution
A method of driving the image sensor that involves concurrently transferring charges from the photoelectric conversion device to the charge storage device, performing correlated double sampling operations to read out image and light noise signals, and generating a compensated image signal by subtracting a multiplied light noise value from the image signal, with the compensation ratio determined by the scan sequence of the unit pixel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If accumulated charges are stored in a charge storage device during photoelectric conversion, then global shutter functionality is achieved, but light noise (leakage current, dark current) accumulates causing image quality degradation
Solution Approach 1:
The patent extracts the harmful light noise component from the accumulated charge signal by performing a second correlated double sampling operation specifically to read out and separate the light noise signal, which is then subtracted from the image signal to eliminate its harmful effects
Solution Approach 2:
The patent changes the temporal parameter by introducing a second read-out period with different timing characteristics compared to the first read-out period, allowing differentiation between image signals and light noise signals through their distinct temporal patterns
2Loss of time
If light noise signal is read out during the same period as image signal, then read-out time is reduced, but light noise contamination occurs in image signal
Solution Approach 1:
The patent segments the read-out process into two distinct periods: a first read-out period for reading image signals and a second read-out period for reading light noise signals. This temporal segmentation allows separate acquisition of both signal types without mutual contamination, maintaining signal purity while managing read-out time
3Manufacturing precision
If compensation ratio is applied to light noise signal, then image quality is improved, but calculation complexity increases
Solution Approach 1:
The patent applies a compensation ratio parameter that adjusts the light noise signal based on the scan sequence position of unit pixels. This parameter change compensates for variations in light noise accumulation across different scan lines, improving image quality through a relatively simple multiplicative operation rather than complex algorithms
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 effectively prevents image quality degradation by accurately accounting for light noise variations across scan sequences, resulting in improved image quality and reduced distortion in global shutter CMOS image sensors.
Implementation Method 1
accumulated charges generated by a photoelectric conversion device
Data Source
AI summary
An image sensor includes a pixel array including at least one unit pixel configured to generate accumulated charges, a correlated double sampler configured to perform a correlated double sampling operation to extract an effective signal component based on a signal component and a reset component from the unit pixel for at least first and second read-out periods, the correlated double sampler configured to read out an image signal during the first read-out period and to read out a light noise signal during the second read-out period, an analog-digital converter configured to convert the image signal into a first digital signal and to convert the light noise signal into a second digital signal and an image compensator configured to generate a compensated image signal based on the second digital signal and the first digital signal.