OLED Pixel Driving Circuit With Bootstrap Compensation for Mura
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Solution Overview
Problem
Existing OLED displays suffer from the Mura phenomenon due to differences in threshold voltages of TFTs, which cause uneven display brightness, particularly exacerbated by varying drive voltages received through impedance-laden power-supply lines, affecting visual experience.
Innovation Solution
A pixel drive circuit incorporating an energy-storage capacitor, bootstrap capacitor, and multiple switching transistors to compensate for threshold voltage and drive voltage variations, ensuring even brightness by decoupling current flow from these factors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional pixel drive circuits with threshold voltage compensation are used, then threshold voltage variations are compensated, but drive voltage variations due to power-supply line impedance are not compensated, resulting in Mura phenomenon
Solution Approach 1:
The patent introduces a feedback mechanism where the actual drive voltage at the pixel circuit is sensed and fed back to the data writing circuit. The data writing circuit adjusts the data voltage based on the feedback signal to compensate for drive voltage variations caused by power-supply line impedance, thereby eliminating the Mura phenomenon and improving display uniformity
Solution Approach 2:
The patent introduces an intermediary sensing circuit and feedback signal transmission path between the pixel circuit and the data writing circuit. This intermediary mechanism enables the system to detect and compensate for drive voltage variations without directly modifying the power-supply line, thus resolving the contradiction between threshold voltage compensation and display uniformity
2Area of stationary object
If the display panel size is increased, then display area is enlarged, but power-supply line impedance effects are amplified, worsening the Mura phenomenon
Solution Approach 1:
The patent segments the large display panel into multiple scanning zones, with each zone having independent scanning control. This segmentation allows the feedback compensation mechanism to be applied independently to each zone, enabling effective compensation for drive voltage variations even in large-scale displays, thus maintaining display uniformity across the entire panel
3Reliability
If complex compensation circuits are added to eliminate Mura phenomenon, then display uniformity is improved, but circuit complexity and power consumption increase
Solution Approach 1:
The patent designs the feedback compensation mechanism to be integrated into the existing pixel drive circuit structure, where the same data writing circuit performs both threshold voltage compensation and drive voltage compensation functions. This multi-functionality approach improves display uniformity without significantly increasing circuit complexity, as the compensation functions share common circuit elements and control logic
Data Source
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AI summary
A pixel drive circuit and a display panel are provided in the disclosure. In the pixel drive circuit (100, 100'), a pre-charge loop (L1) is configured to charge a bootstrap capacitor (C2) in a reset phase to make a voltage at a first terminal of the bootstrap capacitor(C2) reach a value of a drive voltage, and the bootstrap capacitor (C2) is configured to receive a data voltage in a data-writing phase to charge the energy-storage capacitor (C1), so that a voltage at a control terminal of a drive transistor (M) can be adjusted to reach a value of a second voltage, and the drive transistor (M) is configured to drive a light-emitting element (OLED) in the light-emitting phase to emit lights according to the second voltage received and the drive voltage, thereby eliminating uneven display brightness.