X-ray Detector Pixel With Dynamic Capacitance Switching
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Solution Overview
Problem
X-ray detectors face limitations in dynamic range and signal-to-noise ratio due to fixed sensitivity settings, leading to degraded image quality and increased exposure to harmful radiation, as they struggle to handle a wide range of x-ray signals effectively.
Innovation Solution
A radiation detector pixel with an actuator device that automatically shifts electric charges between capacitances, allowing for adjustable sensitivity settings during exposure, enabling both high and low sensitivity range imaging without losing information, and using a field effect transistor for precise control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a low sensitivity setting is chosen to detect strong radiation signals, then the dynamic range is sufficient to avoid saturation, but the signal to noise ratio is degraded due to readout noise dominating weak signals
Solution Approach 1:
The patent implements dynamic sensitivity adjustment by switching between different capacitor configurations (single capacitor for low sensitivity, dual capacitors in parallel for high sensitivity) based on the radiation signal strength. This allows the system to adapt its sensitivity in real-time, using high sensitivity for weak signals to improve signal-to-noise ratio and low sensitivity for strong signals to avoid saturation.
Solution Approach 2:
The invention changes the electrical parameters of the pixel by altering the total capacitance value dynamically. By switching between different capacitance configurations (C1 alone vs. C1+C2 in parallel), the system adjusts its sensitivity parameter to match the radiation intensity, thereby optimizing both dynamic range and signal-to-noise ratio across different operating conditions.
2Measurement precision
If a high sensitivity setting is used to improve signal to noise ratio for weak radiation, then the signal to noise ratio is improved, but the dynamic range is exceeded causing saturation of the readout chain
Solution Approach 1:
The system dynamically switches between high and low sensitivity modes based on the detected signal strength. For weak radiation signals, the dual capacitor configuration provides high sensitivity to improve signal-to-noise ratio. For strong signals, the system switches to single capacitor mode to reduce sensitivity and prevent saturation, thus adapting to different radiation levels in real-time.
Solution Approach 2:
The invention dynamically changes the capacitance parameter to control sensitivity. By switching between different capacitance values (higher total capacitance for high sensitivity, lower total capacitance for low sensitivity), the system adjusts its operating parameter to match the radiation intensity, preventing both saturation and noise domination.
3Device complexity
If a fixed sensitivity setting is used for all pixels, then the device complexity is reduced, but the ability to handle a wide range of x-ray signals is limited
Solution Approach 1:
The patent segments the capacitance function into multiple independent capacitors (C1 and C2) that can be selectively connected in parallel or individually. This segmentation allows each capacitor to serve different sensitivity ranges, with C1 handling high sensitivity measurements and C2 providing additional capacitance for low sensitivity measurements, thereby expanding the overall signal range handling capability.
Solution Approach 2:
The invention makes the pixel structure multi-functional by enabling it to operate in multiple sensitivity modes using the same physical components. The same pixel with switched capacitor configurations can handle both weak and strong radiation signals, eliminating the need for separate pixels for different sensitivity ranges while maintaining adaptability across a wide signal 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 solution allows for improved dynamic range and signal-to-noise ratio, enabling better image quality with reduced exposure to x-ray radiation by automatically adjusting sensitivity settings, allowing for the selection of optimal images based on radiation levels, and minimizing the loss of information during readout.
Implementation Method 1
Each pixel may contain a collection device for the signal in form of e.g. a photodiode to convert the optical photons into electrons
Implementation Method 2
X-ray converters transform x-ray radiation into optical photons either using the indirect conversion with scintillators, by converting x-ray radiation into light
Data Source
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AI summary
An x-ray detector and its pixel circuit are described, that allow to cover a large dynamic range with automatic selection of the sensitivity setting in each pixel, thus providing improved signal to noise ratio with all exposure levels. X-ray detectors are required to cover a large dynamic range. The largest exposure determines the required pixel capacitance. However, a large pixel capacitance gives a bad signal to noise ratio with small exposures e.g. in the dark parts of the image. This invention disclosure describes several approaches to provide automatic sensitivity selection in the pixels. This ensures that low signals are stored in a small capacitor or read out with a high sensitivity with corresponding good signal to noise ratio, while larger signals are stored in larger capacitors or are read out with lower sensitivity so that no information is lost.