Active Pixel Sensor With Dynamic Conversion Gain for Low-Dose Imaging
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Solution Overview
Problem
In medical and industrial flat panel detectors, the reduction in pixel size and X-ray dose leads to a degraded signal-to-noise ratio due to reduced signal intensity, which existing active pixel sensors struggle to adapt to, resulting in compromised imaging quality.
Innovation Solution
An active pixel sensor design that includes a light sensing device, an amplification sub-circuit, an adjustment sub-circuit, and a read sub-circuit, where the adjustment sub-circuit dynamically adjusts the conversion gain in response to control signals, allowing for adaptable sensitivity to varying light intensities by modifying capacitance values or using components like voltage-controlled liquid crystal capacitors and varactor diodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel size is reduced to increase the number of pixels in the array, then the spatial resolution is improved, but the signal intensity is reduced leading to degraded signal-to-noise ratio
Solution Approach 1:
The patent implements a dynamic gain adjustment mechanism where the conversion gain of the photodiode is adaptively changed based on the detected light intensity. When signal intensity is low (as in small pixels), the gain is increased to amplify the signal. This dynamic adaptation resolves the contradiction by allowing small pixels to maintain high signal-to-noise ratio through gain compensation, while large pixels operate with appropriate gain to avoid saturation.
Solution Approach 2:
The patent changes the electrical parameter (conversion gain) of the photodiode based on operating conditions. By adjusting the conversion gain parameter according to light intensity levels, the system optimizes signal-to-noise ratio for small pixels while preventing saturation in large pixels, thus resolving the trade-off between pixel size and signal quality.
2Object-affected harmful factors
If the X-ray dose is reduced to lower the radiation risk, then the safety is improved, but the signal intensity is reduced leading to degraded signal-to-noise ratio
Solution Approach 1:
The dynamic gain adjustment mechanism allows the system to compensate for reduced signal intensity caused by lower X-ray doses. By increasing the conversion gain when signal levels are low, the system maintains adequate signal-to-noise ratio even with reduced radiation exposure, thus resolving the contradiction between safety and image quality.
Solution Approach 2:
The system uses feedback from the detected signal intensity to adjust the conversion gain. When the signal from reduced X-ray dose is detected to be weak, the feedback mechanism increases the gain to maintain signal-to-noise ratio, allowing safe low-dose operation without compromising image quality.
3Device complexity
If a fixed conversion gain is used in the active pixel sensor, then the device complexity is reduced, but the adaptability to varying light intensities is worsened
Solution Approach 1:
The patent introduces dynamic gain adjustment capability to the active pixel sensor, allowing the conversion gain to vary with light intensity conditions. This dynamic feature improves adaptability across different imaging scenarios while adding controlled complexity only where needed for gain adjustment, resolving the contradiction between simplicity and versatility.
Solution Approach 2:
The conversion gain parameter is made variable rather than fixed, allowing the system to adapt to different light intensity conditions. This parameter change enables the sensor to optimize performance across various scenarios from low-light to high-light conditions, achieving versatility without excessive complexity.
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 active pixel sensor effectively enhances sensitivity and extends the detection range, preventing signal saturation and improving imaging quality across different light intensity scenarios, thereby addressing the degradation of signal-to-noise ratio.
Implementation Method 1
a light sensing device configured to convert light sensed by the light sensing device into charges
Implementation Method 2
using components like voltage-controlled liquid crystal capacitors and varactor diodes
Implementation Method 3
adjustment sub-circuit configured to adjust, in response to a first control signal, a conversion gain
Data Source
AI summary
The present disclosure provides an active pixel sensor and a flat panel detector. The active pixel sensor includes: a light sensing device configured to convert light sensed by the light sensing device into charges and supply the charges to a floating diffusion node; an amplification sub-circuit configured to amplify a signal according to a potential at the floating diffusion node and output the amplified signal through the output terminal; an adjustment sub-circuit configured to adjust, in response to a first control signal, a conversion gain from an amount of the light sensed by the light sensing device to the potential at the floating diffusion node; and a read sub-circuit configured to transmit a voltage of the input terminal of the read sub-circuit to the output terminal of the read sub-circuit according to a scan signal provided by the scan line.