Pixel Circuit Threshold Voltage Compensation for X-Ray Detectors
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Solution Overview
Problem
In X-ray flat panel detectors, the consistency of thin-film transistors in each pixel is severely affected by technological limitations and size, leading to noise susceptibility in accumulated electric charges, low signal-to-noise ratio, and varying noise amplitudes across pixels, which degrade image quality.
Innovation Solution
A pixel circuit that includes a photoelectric conversion circuit, reset circuit, amplifying circuit, control circuits, and storage circuit, capable of compensating the threshold voltage of the amplifying transistor, allowing for internal integration of electric charges and reduced noise, thereby enhancing readout accuracy and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the pixel circuit uses thin-film transistors for photoelectric conversion and signal processing, then the detector can be manufactured with planar technology and integrated structures, but the transistor consistency deteriorates due to technological limitations and size constraints
Solution Approach 1:
The patent implements a feedback mechanism where the pixel circuit measures its own threshold voltage offset and automatically compensates for it. The circuit includes a threshold voltage compensation unit that detects the actual threshold voltage of the amplifying transistor and adjusts the operating point accordingly, creating a closed-loop system that eliminates the need for high transistor consistency while maintaining signal quality
Solution Approach 2:
The pixel circuit performs self-diagnosis and self-correction by internally measuring its own threshold voltage characteristics and automatically adjusting its operation to compensate for deviations. This self-service approach allows each pixel to independently correct its own threshold voltage errors without requiring external calibration or high manufacturing precision
2Measurement precision
If the pixel circuit accumulates electric charges to improve signal detection, then the signal-to-noise ratio should improve, but noise susceptibility increases due to transistor inconsistency
Solution Approach 1:
The circuit uses feedback to continuously monitor and correct threshold voltage drift that would otherwise cause noise accumulation during charge integration. By dynamically adjusting the operating point based on actual transistor characteristics, the circuit maintains optimal signal-to-noise ratio throughout the accumulation period
Solution Approach 2:
The patent performs preliminary threshold voltage compensation before the signal accumulation process begins. By pre-calibrating and correcting the threshold voltage offset at the start of each integration period, the circuit prevents noise susceptibility from developing during charge accumulation, ensuring clean signal integration
3Adaptability or versatility
If the pixel circuit uses varying transistor characteristics across pixels, then manufacturing flexibility increases, but noise amplitude varies across pixels degrading image quality
Solution Approach 1:
The patent implements local quality by providing each pixel with its own dedicated threshold voltage compensation unit that independently measures and corrects the specific transistor characteristics of that pixel. This localized approach allows each pixel to be optimized for its own unique characteristics while maintaining uniform image quality across the entire detector array
Solution Approach 2:
The circuit dynamically changes operating parameters based on measured threshold voltage characteristics. By adjusting the gate voltage and other operating points according to the actual transistor parameters, the circuit maintains consistent signal output across pixels with varying manufacturing characteristics, ensuring uniform image quality
4Productivity
If the pixel circuit reads out analog signals quickly to improve imaging speed, then the imaging speed increases, but readout accuracy may be compromised without proper signal conditioning
Solution Approach 1:
The patent performs preliminary signal conditioning including threshold voltage compensation and offset correction before the readout process begins. By preparing and correcting the signal in advance during the integration period, the circuit enables rapid readout without sacrificing accuracy, as the signal is already optimized for conversion
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 pixel circuit effectively compensates the threshold voltage of the amplifying transistor, reducing noise levels, improving the signal-to-noise ratio, and enabling quicker and more accurate analog signal readout, while minimizing external chip integration costs.
Implementation Method 1
the visible light is converted by the photodiode array into an analog signal of the image
Data Source
AI summary
Embodiments of the present disclosure provide a pixel circuit and a drive method thereof, and a detector including the pixel circuit. The pixel circuit includes a photoelectric conversion circuit, a reset circuit, an amplifying circuit, a first control circuit, a second control circuit, a storage circuit, and an output circuit. The photoelectric conversion circuit is configured to convert an optical signal into an electric signal. The reset circuit is configured to reset a voltage of the first node. The amplifying circuit is configured to amplify the voltage of the first node. The first control circuit is configured to control a voltage of the second node. The second control circuit is configured to control a voltage of the third node. The storage circuit is configured to store an electric charge corresponding to the voltage outputted from the amplifying circuit. The output circuit is configured to output the stored electric charge.