Pixel Circuit Threshold Voltage Compensation for Micro-OLED Mura
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Solution Overview
Problem
Micro-OLED panels suffer from uneven brightness due to mismatched driving transistors and OLEDs, causing the Mura effect, which existing pixel structures have not effectively addressed.
Innovation Solution
A novel pixel circuit design incorporating multiple transistors and capacitors that cancel the influence of threshold voltage offsets, allowing for uniform brightness by controlling the driving current based on input data and threshold voltage information stored in capacitors, thereby minimizing the Mura effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional pixel structures are used, then the device complexity is low, but brightness non-uniformity occurs due to transistor mismatch
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks: a first sub-pixel circuit with first and second driving transistors for threshold voltage compensation, a second sub-pixel circuit for current mirroring, and associated capacitors for voltage storage. This segmentation allows each block to perform a specific function, achieving brightness uniformity through coordinated operation while managing complexity through modular design.
Solution Approach 2:
The circuit performs preliminary threshold voltage compensation during the initialization phase before the display phase. The first driving transistor's threshold voltage is compensated in advance by controlling its gate voltage, and this compensated voltage is stored in capacitors. This preliminary action ensures that subsequent current mirroring operates with corrected reference values, eliminating brightness non-uniformity before it manifests.
2Manufacturing precision
If threshold voltage compensation is implemented, then brightness uniformity improves, but the pixel circuit complexity increases
Solution Approach 1:
The circuit merges the threshold voltage compensation function and current mirroring function into a unified pixel structure. The first driving transistor serves both as a compensation element and as part of the current mirror, while capacitors serve dual purposes of voltage storage and signal coupling. This merging reduces overall complexity compared to implementing separate compensation and driving circuits.
Solution Approach 2:
The first driving transistor performs multiple functions: it compensates for threshold voltage offsets, provides a reference voltage for the current mirror, and controls the compensation capacitor charging. The second driving transistor similarly serves multiple roles in current mirroring and output control. This multi-functionality reduces the total number of components needed while achieving brightness uniformity.
3Manufacturing precision
If current mirroring is used to improve brightness uniformity, then manufacturing precision improves, but device complexity increases
Solution Approach 1:
The circuit uses current mirroring to create a copy of the compensated reference current from the first sub-pixel circuit and apply it to the light emitting element. By copying the voltage and current characteristics through matched transistors, the circuit achieves brightness uniformity without requiring separate compensation circuits for each pixel, thereby managing complexity through efficient use of the mirroring principle.
Data Source
AI summary
A pixel circuit of a display panel includes a driving transistor, first to fifth transistors, and a light emitting device. The driving transistor includes a first terminal, a second terminal and a gate terminal. The first transistor is coupled between a power supply terminal and the first terminal of the driving transistor. The second transistor is coupled between the first terminal of the driving transistor and the gate terminal of the driving transistor. The third transistor is coupled between the second terminal of the driving transistor and the gate terminal of the driving transistor. The fourth transistor is coupled between a data input terminal and the second terminal of the driving transistor. The fifth transistor is coupled to the second terminal of the driving transistor. The light emitting device is coupled between the fifth transistor and a reference voltage terminal.