Solid-State Image Sensor Reset Control for Low-Light Dynamic Range
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Solution Overview
Problem
Existing solid-state imaging elements fail to effectively convert small amounts of photoelectrically-converted electric charges into image signals, leading to reduced dynamic range and potential signal deterioration under low illumination, with threshold values varying across pixels.
Innovation Solution
A solid-state imaging element with a photoelectric conversion unit, a first electric charge holding unit, a comparator, a reset unit, and a counting unit, where the reset potential changes in time series, allowing for accurate conversion and counting of electric charges, and includes a read-out circuit and signal processing units to generate digital signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a fixed threshold value is used for detecting electric charges, then the detection method is simple, but the signal deteriorates under low illumination and the threshold varies across pixels
Solution Approach 1:
The patent applies dynamics by making the threshold value variable rather than fixed. The threshold is dynamically adjusted based on the potential change amount detected during the accumulation period, allowing the system to adapt to different illumination conditions and maintain accurate detection across varying light levels.
Solution Approach 2:
The patent changes the parameter of threshold value from a static fixed value to a dynamic value that varies according to the potential change amount. This parameter change enables the threshold to adapt to different accumulation conditions and illumination levels, resolving the contradiction between simplicity and accuracy.
2Device complexity
If a fixed accumulation capacity is used in the photoelectric conversion unit, then the device structure is simple, but the dynamic range is limited
Solution Approach 1:
The patent applies dynamics by enabling the accumulation capacity to be virtually extended through multiple accumulation periods. Instead of increasing the physical capacity, the system dynamically accumulates charges across multiple cycles and uses potential change detection to represent the total amount, thereby expanding the dynamic range without increasing device complexity.
Solution Approach 2:
The patent transitions from a single-dimension accumulation approach (single capacity) to a multi-dimensional approach by accumulating charges across multiple time periods. The accumulation capacity is extended into the time dimension, allowing the system to handle a wider range of light intensities without increasing the physical storage capacity.
3Adaptability or versatility
If the accumulation capacity is enlarged to increase dynamic range, then the dynamic range improves, but the photoelectric conversion unit size increases
Solution Approach 1:
The patent uses dynamics to achieve virtual capacity expansion through time-based multi-cycle accumulation. The system maintains a fixed physical capacity but achieves effective capacity enlargement by accumulating charges across multiple periods and using potential change detection, avoiding any increase in photoelectric conversion unit size.
Solution Approach 2:
The patent changes the approach from increasing physical capacity to changing the operational parameters (accumulation period count and potential change detection). This allows the dynamic range to be enlarged through parameter optimization rather than physical expansion, maintaining compact device dimensions.
4Ease of operation
If small amounts of electric charges are not converted to image signals, then the device operation is simple, but the signal is lost under low illumination
Solution Approach 1:
The patent replaces the conventional mechanical/threshold-based detection system with a potential change detection system. Instead of using a fixed voltage threshold, the system detects changes in potential during accumulation, enabling it to reliably detect even small amounts of electric charges while maintaining operational simplicity.
Solution Approach 2:
The patent changes the detection parameter from fixed threshold voltage to potential change amount. This parameter change enables the system to detect small charge amounts that would be missed by fixed threshold methods, improving reliability under low illumination without complicating the operation.
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 enables the conversion of small electric charge amounts into image signals, maintaining dynamic range and accuracy across varying illumination levels by adjusting reset potentials and coefficients, thereby enhancing image quality.
Implementation Method 1
a photoelectric conversion unit that generates electric charges according to an amount of received light
Data Source
AI summary
[Object] To provide a solid-state imaging element and an imaging device that can enlarge the dynamic range and convert even a small amount of photoelectrically-converted electric charges into an image signal. [Solving Means] According to the present disclosure, provided is a solid-state imaging element including a photoelectric conversion unit that generates electric charges according to an amount of received light, a first electric charge holding unit that is connected to the photoelectric conversion unit via a first node, a comparator that outputs a first signal when a potential of the first node and a predetermined potential coincide with each other, a reset unit that sets the first node to a reset potential according to the first signal, and a counting unit that counts and outputs the first signal, and in a first mode, the reset potential applied to the first node changes in time series.