X-ray Detector Pixel With Multiple Charge-Storage Capacitors
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Solution Overview
Problem
Current digital X-ray imaging systems face limitations in reducing electronic noise, particularly at low dose X-ray imaging applications, due to the structure of the pixel in detectors like CMOS detectors.
Innovation Solution
The implementation of a digital X-ray detector with multiple pixels, each equipped with a pinned photodiode and at least two charge-storage capacitors, along with control circuitry that selectively directs photocharge to these capacitors based on radiation dose, utilizing correlated double sampling to separate and remove reset noise from the signal, thereby reducing electronic noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional pixel structure with a single charge-storage device is used, then the device complexity is low, but electronic noise cannot be effectively reduced at low dose X-ray imaging applications
Solution Approach 1:
The pixel structure is segmented into multiple charge-storage devices (first charge-storage device and second charge-storage device) coupled to a single photodiode. This segmentation allows separate storage of signal and reset noise, enabling effective noise reduction while managing device complexity through structured division of functions.
Solution Approach 2:
A transfer gate is introduced as an intermediary component between the photodiode and the multiple charge-storage devices. This transfer gate mediates the selective routing of photocharge to different storage devices based on timing signals, enabling correlated double sampling without requiring direct complex connections from the photodiode to multiple capacitors.
2Measurement precision
If multiple charge-storage capacitors are added to each pixel, then electronic noise can be reduced through correlated double sampling, but the device complexity increases
Solution Approach 1:
The pixel structure is segmented into multiple charge-storage devices (first charge-storage device and second charge-storage device) coupled to a single photodiode. This segmentation allows separate storage of signal and reset noise, enabling effective noise reduction while managing device complexity through structured division of functions.
Solution Approach 2:
The multiple charge-storage devices serve multiple functions: one stores the photocharge signal while another stores the reset noise for subtraction. This multi-functionality allows a single pixel structure to perform both signal integration and noise characterization, improving measurement precision without requiring separate dedicated circuits for each function.
3Measurement precision
If correlated double sampling is implemented with multiple charge-storage devices, then reset noise can be separated and removed from the signal, but the device complexity and control requirements increase
Solution Approach 1:
The control circuitry employs periodic action through timing signals that rhythmically control the transfer gates. During integration, the first transfer gate is activated to store photocharge in the first charge-storage device. During readout, the second transfer gate is activated to transfer charge to the second charge-storage device for noise measurement. This periodic switching enables correlated double sampling with manageable control complexity.
Solution Approach 2:
The pixel structure performs self-service by using its own multiple charge-storage devices to automatically separate and store both the signal and reset noise components. The correlated double sampling process is self-contained within each pixel, eliminating the need for external complex noise characterization equipment or additional processing circuits.
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 reduces electronic noise and improves image quality by accurately separating and correcting noise components, enhancing the dynamic range and temporal resolution of X-ray imaging systems.
Implementation Method 1
a scintillator configured to absorb radiation emitted from the X-ray source and to emit optical photons in response to the absorbed radiation
Implementation Method 2
each pinned photodiode is configured to generate a photocharge in response to the absorbed optical photons
Data Source
AI summary
A digital X-ray imaging system is provided. The digital X-ray imaging system includes an X-ray source and a digital X-ray detector. The digital X-ray detector includes a scintillator configured to absorb radiation emitted from the X-ray source and to emit optical photons in response to the absorbed radiation. The digital X-ray detector also includes multiple pixels, each pixel including a pinned photodiode and at least two charge-storage capacitors coupled to the pinned photodiode, wherein each pixel is configured to absorb the optical photons emitted by the scintillator and each pinned photodiode is configured to generate a photocharge in response to the absorbed optical photons. The digital X-ray detector further includes control circuitry coupled to each pixel of the multiple pixels and configured to selectively control a respective flow of the photocharge generated by the pinned photodiode to a respective charge-storage capacitor of the at least two charge-storage capacitors during integration.