CMOS Dental X-Ray Sensor Pixel Array Architecture
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Solution Overview
Problem
Conventional dental x-ray systems using film expose patients to high x-ray doses, are costly, and pose environmental disposal issues, while solid-state sensors face challenges in constructing large pinned photodiodes for optimal pixel size and sensitivity, leading to increased exposure times and costs due to reduced fill-factor and increased readout times.
Innovation Solution
The image sensor employs a two-dimensional array of pixel sensors with capacitors, light sensors, and a controller that allows controlled charge transfer and conversion, varying the number of photodiodes contributing to each capacitor to prevent saturation and optimize light intensity computation, and includes distributed analog-to-digital converters and gain control mechanisms to enhance dynamic range and readout efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional film is used for dental x-ray imaging, then the equipment is simple and cost is low, but the patient is exposed to high x-ray doses and film processing chemicals pose environmental disposal problems
Solution Approach 1:
The patent replaces the mechanical film-based imaging system with a solid-state CMOS sensor system. The film is substituted by an array of pixel elements with photodiodes that convert x-ray induced light directly into electrical signals, eliminating the need for chemical processing and reducing patient exposure while maintaining imaging functionality.
Solution Approach 2:
The patent employs a composite structure combining scintillation material (for x-ray to light conversion) with CMOS photodiode arrays (for light detection and signal processing). This composite approach enables the sensor to efficiently convert x-ray energy into detectable electrical signals with high sensitivity and reduced dosage requirements.
2Measurement precision
If the pixel size is reduced to increase the number of pixels for higher resolution, then the image detail improves, but the fill-factor decreases and readout time increases
Solution Approach 1:
The patent divides the imaging array into multiple pixel elements, each with its own photodiode and readout circuitry. This segmentation allows parallel readout of multiple pixels simultaneously, maintaining high resolution while reducing total readout time compared to sequential readout methods.
Solution Approach 2:
The patent implements dynamic control of the readout process through programmable gain amplifiers and variable readout rates. The system can adaptively adjust readout parameters based on imaging conditions, optimizing the balance between resolution and readout speed for different clinical scenarios.
3Measurement precision
If the pixel size is reduced to increase the number of pixels for higher resolution, then the image detail improves, but the fill-factor decreases leading to reduced sensitivity
Solution Approach 1:
The patent merges the photodiode, amplifier, and readout circuitry into an integrated pixel element structure. This integration allows smaller pixel sizes while maintaining adequate fill-factor by combining multiple functions within each pixel, preventing sensitivity loss that would normally accompany pixel size reduction.
Solution Approach 2:
The patent employs programmable gain amplifiers that can dynamically adjust the amplification factor based on the detected signal level. This parameter adjustment compensates for the reduced fill-factor in smaller pixels, maintaining overall sensitivity while enabling higher resolution through increased pixel count.
4Reliability
If larger pinned photodiodes are constructed for optimal pixel size and sensitivity, then the fill-factor improves, but manufacturing difficulty increases
Solution Approach 1:
The patent segments the large photodiode structure into multiple smaller photodiode elements within each pixel. This segmentation makes manufacturing more feasible while maintaining overall sensitivity through the combined response of multiple elements, avoiding the difficulties of constructing and handling large single photodiodes.
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 reduces x-ray exposure times, improves image quality, and decreases the cost and environmental impact by optimizing pixel sensitivity and readout efficiency, while maintaining high image quality and reducing the need for extensive lens systems.
Implementation Method 1
a layer of scintillation material is used to convert the x-rays to visible light
Implementation Method 2
The photodiode generates and stores a charge that is related to the amount of light that was received by the photodiode
Data Source
AI summary
An image sensor and a method for using the same to capture an x-ray image are disclosed. The image sensor includes an output bus, a two dimensional array of pixel sensors that receives light from a layer of scintillation material and a controller. Each pixel sensor includes a capacitor, a plurality of light sensors, a charge converter and a transfer gate. Each of the light sensors includes a photodiode and a photodiode transfer gate that connects the photodiode to the capacitor. During readout, the charge on selected ones of the photodiodes is transferred to the capacitor. The charge on the capacitor is converted to a signal that is coupled to the output bus through the transfer gate by the controller. The number of photodiodes that are connected to the capacitor during the readout can be controlled to assure that the charge converter does not saturate.