Dual Gate TFT Pixel Multiplexing for Digital X-Ray Detectors
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Solution Overview
Problem
Digital X-ray detectors require a reduction in the number of readout integrated circuits (ROICs) to lower costs while maintaining signal-to-noise ratio (SNR) and frame-rate performance, as current multiplexing schemes do not provide SNR benefits and require two readout times for each row.
Innovation Solution
A dual gate TFT structure is used to multiplex charge from adjacent pixels onto a common data line, allowing for a 2× reduction in the number of data lines and enabling horizontal charge binning with improved SNR, frame-rate in 2× and 4× charge bin modes without reducing full resolution frame-rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the number of readout integrated circuits (ROICs) is reduced to lower costs, then manufacturing cost decreases, but signal-to-noise ratio (SNR) deteriorates and frame-rate performance is compromised
Solution Approach 1:
The patent merges multiple pixel signals onto a single shared data line using a dual-gate TFT switch structure. The first gate controls pixel selection while the second gate controls charge transfer timing, enabling multiple pixels to share one data line without signal interference. This merging approach reduces the number of ROICs needed while maintaining signal integrity and SNR through controlled charge transfer.
Solution Approach 2:
The patent employs dynamic control of the dual-gate TFT switches to manage signal routing. The first gate dynamically selects which pixel to readout, while the second gate dynamically controls when charge transfers to the shared data line. This dynamic switching enables time-multiplexed readout that maintains high SNR despite signal sharing, resolving the contradiction between cost reduction and performance maintenance.
2Device complexity
If multiplexing schemes are used to reduce the number of data lines, then device complexity decreases, but signal-to-noise ratio (SNR) deteriorates and readout time increases
Solution Approach 1:
The patent merges multiple pixel signals onto a single shared data line using a dual-gate TFT switch structure. The first gate controls pixel selection while the second gate controls charge transfer timing, enabling multiple pixels to share one data line without signal interference. This merging approach reduces the number of ROICs needed while maintaining signal integrity and SNR through controlled charge transfer.
Solution Approach 2:
The dual-gate TFT switch acts as an intermediary between the pixel and the shared data line. The second gate serves as a mediator that controls charge transfer timing, ensuring that charge is transferred only when the shared data line is ready to receive it. This intermediary control prevents signal conflicts and maintains high SNR despite the reduced number of data lines.
3Productivity
If charge is transferred from multiple pixels simultaneously onto a single data line, then productivity increases through faster readout, but manufacturing precision requirements increase
Solution Approach 1:
The patent segments the control function into two separate gates: the first gate handles pixel selection and the second gate handles charge transfer timing. This segmentation allows independent optimization of each control function, reducing the impact of threshold voltage variations. By separating these functions, the system achieves high-speed simultaneous readout without requiring extremely tight manufacturing precision.
Solution Approach 2:
The patent utilizes the second gate to dynamically change the transfer threshold parameter. By adjusting the second gate voltage, the system can control when charge transfers to the shared data line, compensating for manufacturing variations in TFT threshold voltages. This parameter control enables simultaneous charge transfer from multiple pixels while maintaining signal integrity and achieving high frame rates.
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 reduces the number of external ROICs, enhances SNR through reduced data line capacitance, and improves frame-rate in multiplexing modes compared to standard readout schemes, achieving lower-cost DXDs with maintained performance.
Implementation Method 1
The diode element collects light that is converted from Xrays incident on a scintillator material
Data Source
AI summary
A detector having an array of pixels arranged in columns and rows. Each of the pixels has a photosensor and a switch device. The switch devices in each pair of row-adjacent pixels are connected to a common data line and a common bottom gate line. A pair of top gate lines are each connected to one of the pair of row-adjacent pixels.