Radiation Imaging System Transistor Threshold Stabilization
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Solution Overview
Problem
Radiation imaging systems face challenges in maintaining image quality due to threshold voltage shifts in transistors, which result in fixed pattern noise when OFF voltages are applied for extended periods, and this noise cannot be correctly removed if the imaging and offset states differ.
Innovation Solution
The system incorporates a scanning circuit that supplies different OFF voltages to transistors during a conditioning mode, ensuring a duty ratio not lower than the lowest in image capturing modes, to stabilize the threshold voltage and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If an OFF voltage is applied to the gate of the transistor for a long time, then the transistor can maintain its state, but a threshold shift occurs causing fixed pattern noise
Solution Approach 1:
The patent applies periodic switching between different OFF voltages (first OFF voltage and second OFF voltage) to the transistor gate. This periodic action prevents threshold shift by avoiding prolonged exposure to a single voltage level, thereby eliminating fixed pattern noise while maintaining the transistor in its OFF state during imaging periods.
Solution Approach 2:
The patent changes the voltage parameter by switching between multiple OFF voltage levels (first OFF voltage and second OFF voltage) rather than maintaining a constant OFF voltage. This parameter change approach stabilizes the transistor threshold voltage and prevents the accumulation of charge that would otherwise cause threshold shift and fixed pattern noise.
2Adaptability or versatility
If the state of the radiation imaging apparatus differs between radiation image and offset image acquisition, then operational flexibility is maintained, but noise components cannot be correctly removed
Solution Approach 1:
The patent performs preliminary conditioning of the transistor threshold voltage by applying alternating OFF voltages before actual imaging. This preliminary action ensures that the transistor is in a stable, known state, allowing accurate offset image acquisition and subsequent noise removal even when transitioning between different imaging modes or conditions.
Solution Approach 2:
The patent uses offset image acquisition and processing as a feedback mechanism to measure and correct for noise components. By acquiring offset images under controlled conditions and using them to subtract noise from radiation images, the system maintains measurement precision despite operational flexibility and state changes.
3Device complexity
If the scanning circuit scans all rows in conditioning mode like in image capturing modes, then the process is simple, but the duty ratio is too low to effectively condition the threshold voltage
Solution Approach 1:
The patent segments the row scanning process by applying different scanning strategies: in conditioning mode, it scans rows in units of at least two rows simultaneously, whereas in image capturing modes it scans in units of at least one row. This segmentation approach increases the duty ratio during conditioning to effectively stabilize threshold voltage, while maintaining simplicity through systematic row-group processing.
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 suppresses threshold voltage shifts, improving image quality by maintaining consistent noise removal across varying imaging states.
Implementation Method 1
each pixel includes a converter configured to generate an electric signal corresponding to radiation
Data Source
AI summary
A radiation imaging system includes pixel array, scanning circuit to scan rows of the pixel array, and readout circuit to read signals from the pixel array. Each pixel includes converter to generate electric signal corresponding to radiation and transistor connected to the converter. The readout circuit reads signal from the converter via the transistor. The system performs image capturing modes and conditioning mode of conditioning a threshold voltage of the transistor. In the conditioning mode, the scanning circuit supplies, to a gate of the transistor, an OFF voltage different from OFF voltages in the image capturing modes. The scanning circuit scans the rows in units of at least one row in the image capturing modes, and scans the rows in units of at least two rows in the conditioning mode.