Divided Pixel Sensor for Wide Dynamic Range Imaging
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Solution Overview
Problem
Existing solid-state image sensing devices face challenges in maintaining a wide dynamic range without losing details in high-brightness areas, leading to issues like shifts in centers of gravity and deteriorated signal-to-noise ratio (S/N) due to variations in sensitivity and exposure among pixels, resulting in false colors and noise.
Innovation Solution
A solid-state image sensing device with a pixel matrix where adjacent pixels are divided into regions with different photosensitivity or exposure conditions, set to opposing conditions in diagonal directions, and an AD conversion part that multiplies the output by an optimal factor to maintain linear output and maximize S/N.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If pixels are divided into regions with different photosensitivity to expand dynamic range, then sensitivity in low-light conditions is improved, but shifts in centers of gravity and false colors occur
Solution Approach 1:
Each pixel is divided into multiple divided pixels with different photosensitivity characteristics (high-sensitivity divided pixels and low-sensitivity divided pixels). This segmentation allows the sensor to capture both low-light and high-light information simultaneously, expanding the dynamic range while maintaining proper center of gravity alignment through symmetric arrangement.
Solution Approach 2:
The patent employs asymmetric arrangement where divided pixels with opposite photosensitivity characteristics are positioned diagonally opposite to each other. This asymmetric positioning around the pixel center maintains the center of gravity at the pixel center, preventing false colors while utilizing different sensitivity characteristics for wide dynamic range imaging.
2Illumination intensity
If pixels with different sensitivity characteristics are used to capture high-brightness information, then dynamic range is expanded, but signal-to-noise ratio deteriorates
Solution Approach 1:
The patent implements feedback mechanisms where the control circuit selectively reads out signals from high-sensitivity or low-sensitivity divided pixels based on the actual lighting conditions. This feedback-based selection ensures optimal signal-to-noise ratio by using high-sensitivity pixels in low-light conditions and low-sensitivity pixels in high-light conditions, while maintaining expanded dynamic range capability.
Solution Approach 2:
The patent changes the photosensitivity parameter of divided pixels within the same pixel structure by controlling impurity concentrations differently in high-sensitivity and low-sensitivity divided pixels. This parameter change enables the same pixel to adapt to different lighting conditions, expanding dynamic range while maintaining high signal-to-noise ratio through appropriate pixel selection.
3Illumination intensity
If multiple divided pixels with different exposure times are used, then saturation in high-brightness areas is prevented, but device complexity increases
Solution Approach 1:
The patent merges multiple divided pixels with different photosensitivity characteristics and exposure times into a single pixel structure. By combining high-sensitivity and low-sensitivity divided pixels within one pixel, the system prevents saturation in high-brightness areas while maintaining a relatively simple overall device structure that can be integrated into standard CMOS or CCD architectures.
4Ease of operation
If divided pixel signals are added after AD conversion, then processing flexibility is improved, but external memory requirements increase
Solution Approach 1:
The patent extracts the signal addition operation from external memory storage and performs it directly in the signal processing circuit before final output. By taking out the addition function from the memory system and implementing it in the readout circuitry, the patent maintains processing flexibility while eliminating the need for additional external memory to store divided pixel signals temporarily.
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 prevents shifts in centers of gravity, maximizes S/N, and achieves a wide dynamic range with higher sensitivity in low light and lower sensitivity in high light conditions without saturation, eliminating the need for external memory and improving S/N at saturation points.
Implementation Method 1
a photoelectric conversion element that converts incident light into signal charge in an amount in response to the amount of light
Data Source
AI summary
A solid-state image sensing device includes: a pixel part in which pixels are arranged in a matrix; and a pixel signal readout part including an AD conversion part that analog-digital (AD)-converts a pixel signal read out from the pixel part. Each of the adjacent pixels or one of the pixels of the pixel part is formed as divided pixels divided into regions with different photosensitivity or amounts of accumulated charge, photosensitivity or exposure time conditions are set for the divided pixels and the photosensitivity or exposure time conditions of the divided pixels provided to be opposed in diagonal directions are set to the same conditions, the pixel signal readout part reads out divided pixel signals of the respective divided pixels of the pixel, and the AD conversion part obtains a pixel signal of one pixel by AD-converting the respective read out divided pixel signals and adding the signals.