4T1C Pixel Driving Circuit Threshold Voltage Compensation
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Solution Overview
Problem
The existing 2T1C AM-OLED pixel unit driving circuit is affected by inconsistencies in threshold voltage, leading to non-uniform brightness across the display screen due to variations in driving current, which complicates gray scale adjustment.
Innovation Solution
A 4T1C pixel unit driving circuit structure is introduced, comprising four thin film transistors and one storage capacitor, where the third thin film transistor's threshold voltage variations are compensated, ensuring stable driving voltage and current, thereby maintaining uniformity across the display panel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a 2T1C structure is used to simplify the circuit, then device complexity is reduced, but brightness uniformity deteriorates due to threshold voltage variations
Solution Approach 1:
The patent divides the driving function into multiple transistors: T1 for switching, T2 for current driving, T3 for threshold voltage compensation, and T4 for emission control. This segmentation allows each transistor to perform a specific function, with T3 specifically dedicated to compensating threshold voltage variations, thereby resolving the contradiction between circuit simplicity and brightness uniformity.
Solution Approach 2:
The patent introduces T3 as an intermediary component between the data writing stage and the emission stage. T3 acts as a mediator that compensates for threshold voltage variations, ensuring that the driving current remains stable despite variations in transistor characteristics, thus improving brightness uniformity without significantly increasing overall circuit complexity.
2Illumination intensity
If threshold voltage compensation is implemented to improve brightness uniformity, then illumination intensity uniformity is improved, but device complexity increases
Solution Approach 1:
The patent merges the threshold voltage compensation function with the existing pixel structure by integrating T3 into the pixel unit. Rather than adding a completely separate compensation circuit, T3 is combined with the switching and driving transistors, sharing common nodes and capacitors, which reduces the overall complexity increase while achieving brightness uniformity.
Solution Approach 2:
The patent designs T3 to serve multiple functions: it compensates for threshold voltage variations, controls the timing of the emission stage, and works in conjunction with the storage capacitor to maintain stable driving current. This multi-functionality reduces the need for additional dedicated compensation components, thereby limiting the increase in device complexity.
3Illumination intensity
If more transistors are added to compensate for threshold voltage, then brightness uniformity is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent implements a self-compensation mechanism where T3 automatically adjusts for threshold voltage variations in T2 through its own threshold voltage characteristics. The compensation is inherent to the transistor operation and does not require external calibration or high-precision manufacturing, as the circuit self-adjusts to variations in transistor parameters.
Solution Approach 2:
The patent exploits the threshold voltage parameter of T3 to compensate for variations in T2. By designing T3 with specific threshold voltage characteristics, the circuit transforms the parameter variation problem into a compensation opportunity, where the threshold voltage of T3 is used to offset the threshold voltage variations in the driving transistor, reducing manufacturing precision requirements.
Data Source
AI summary
There are provided a pixel unit driving circuit and driving method, pixel unit and display apparatus. The pixel unit driving circuit is used for driving a light-emitting device to emit light, and comprises a first thin film transistor (T1), a second thin film transistor (T2), a third thin film transistor (T3) and a storage capacitor (Cs). A gate of the first thin film transistor (T1) is connected with a control line (Gate), a first electrode thereof is connected with a data line (Data), and a second electrode thereof is connected with a first node (A). One gate of the second thin film transistor (T2) is connected with the control line (Gate) and the other gate is connected with a second scan line (Scan2), a first electrode thereof is connected with the storage capacitor (Cs), and a second electrode thereof is connected with a second node (B). One gate of the third thin film transistor (T3) is connected with the first node (A) and the other gate is connected with the second scan line (Scan2), a first electrode thereof is connected with a power supply (Vdd), and a second electrode thereof is connected with the second node (B). One terminal of the storage capacitor is connected with the first node (A), and the other terminal is connected with the first electrode of the second thin film transistor (T2). One terminal of the light-emitting device is connected with the second node (B), and the other terminal thereof is grounded. The pixel unit driving circuit can reduce an influence on a driving voltage caused by variations in threshold voltage.