Image Sensor Variable Conversion Gain Pixel Array
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Solution Overview
Problem
Current image sensors face challenges in achieving a wide dynamic range, particularly in capturing images with both low-illumination and high-illumination regions simultaneously, as they struggle to balance sensitivity and noise reduction across varying light conditions.
Innovation Solution
The image sensor employs a pixel array with first and second pixels, each connected to different conversion gain control lines, allowing for variable conversion gains based on the amount of incident light, enabling improved sensitivity in low-illumination regions and reduced noise in high-illumination regions by adjusting the capacitance of the charge detection node.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed conversion gain is used in the image sensor, then the circuit design is simple, but the dynamic range is limited and cannot capture both low-illumination and high-illumination regions simultaneously
Solution Approach 1:
The patent implements variable conversion gain by dynamically switching the connection between the charge detection node and capacitive element through control signals. The capacitance value changes from a first value to a second value based on incident light intensity, enabling the sensor to adapt to different illumination conditions and expand dynamic range without requiring multiple fixed-gain circuits
Solution Approach 2:
The patent changes the capacitance parameter of the charge detection node to achieve variable conversion gain. By controlling the capacitance value to switch between a first capacitance value and a second capacitance value, the system optimizes sensitivity for low-illumination regions while reducing noise for high-illumination regions, thereby expanding dynamic range
2Measurement precision
If high conversion gain is used to improve sensitivity in low-illumination regions, then sensitivity is improved, but noise increases in high-illumination regions
Solution Approach 1:
The patent applies different conversion gains to different spatial regions of the image sensor based on local illumination conditions. Low-illumination regions use high conversion gain (first capacitance value) to improve sensitivity, while high-illumination regions use low conversion gain (second capacitance value) to reduce noise, achieving optimized performance for each local area
Solution Approach 2:
The patent dynamically adjusts the conversion gain for each pixel based on the incident light intensity. The control circuit switches the capacitance value in real-time according to the illumination level detected by each pixel, enabling the system to maintain optimal sensitivity-to-noise ratio across varying light conditions
3Adaptability or versatility
If variable conversion gain is implemented to capture wide dynamic range, then both bright and dark regions are clearly represented, but the device complexity increases due to additional control circuits and capacitive elements
Solution Approach 1:
The patent designs the capacitive element and switching circuitry to serve multiple functions: they act as both the charge storage element and the variable gain control mechanism. The same control lines that manage pixel selection also control the capacitance switching, reducing the need for separate control circuits and minimizing additional complexity
Solution Approach 2:
The patent integrates the capacitive element within the existing pixel structure, nesting it alongside the photoelectric conversion element and readout circuit. The variable gain functionality is embedded within the standard pixel architecture rather than adding separate external circuits, thereby minimizing overall device complexity while achieving wide dynamic range
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 allows for a clear representation of both bright and dark regions in an image, effectively enlarging the dynamic range and improving image quality by optimizing conversion gains for varying light conditions.
Implementation Method 1
a photoelectric conversion element configured to generate and accumulate photocharges
Data Source
AI summary
An image sensor includes a pixel array including a plurality of unit pixels arranged along a plurality of rows and a plurality of columns. Each of the unit pixels includes a photoelectric conversion element generating and accumulating photocharges, a charge detection node receiving the photocharges accumulated in the photoelectric conversion element, a readout circuit converting the photocharges accumulated in and output from the charge detection node into an electrical pixel signal, the readout circuit outputting the electrical pixel signal, a capacitive element, and a switching element controlling connection between the charge detection node and the capacitive element. Each of the rows of the pixel array includes first pixels connected to a first conversion gain control line and second pixels connected to a second conversion gain control line.