AMOLED Pixel Compensation Circuit for Brightness Uniformity
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Solution Overview
Problem
The brightness uniformity in AMOLED displays is poor due to nonuniformity in the critical voltages of transistors and threshold voltage drift during light emission, leading to display nonuniformity and other issues.
Innovation Solution
A pixel compensation circuit is introduced, comprising a data signal writing module, high voltage signal writing module, reference voltage generation modules, a driving transistor, a capacitor, and a light emitting device, which writes a voltage including the threshold voltage of the driving transistor to the capacitor and gate of the driving transistor before light emission, maintaining a constant voltage difference across the capacitor terminals during light emission, thereby isolating the driving current from threshold voltage and high voltage signal terminal variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple 2T1C pixel circuit is used for AMOLED display, then device complexity is reduced and manufacturing is simplified, but brightness uniformity deteriorates due to transistor threshold voltage nonuniformity and drift
Solution Approach 1:
The pixel circuit is segmented into multiple functional modules: a compensation module with first and second capacitors for threshold voltage compensation, a storage module with third capacitor for data signal storage, and a driving transistor module. This segmentation allows independent optimization of each module to address brightness uniformity while managing overall complexity.
Solution Approach 2:
The compensation capacitors are pre-charged during a compensation phase before the actual display phase. The first capacitor stores a voltage related to the driving transistor's threshold voltage, and the second capacitor stores a voltage related to the light emitting diode's threshold voltage. This preliminary action compensates for threshold voltage variations before they affect brightness uniformity.
2Manufacturing precision
If transistor threshold voltage compensation is implemented, then brightness uniformity is improved, but device complexity increases due to additional capacitors and circuit modules
Solution Approach 1:
The compensation function is merged into the existing pixel circuit structure by integrating compensation capacitors with the driving transistor and light emitting diode. The first capacitor is connected between the gate and source of the driving transistor, while the second capacitor is connected to the anode of the light emitting diode, combining compensation functionality with the basic pixel structure.
Solution Approach 2:
The compensation capacitors serve multiple functions: they store threshold voltage information, compensate for voltage drift during operation, and maintain stable driving currents. The first capacitor compensates for driving transistor threshold voltage variations, while the second capacitor compensates for light emitting diode threshold voltage variations, providing universal compensation across different transistor and diode variations.
3Reliability
If threshold voltage compensation is performed, then emission brightness stability is improved, but use of energy increases due to additional writing and maintaining of reference voltages
Solution Approach 1:
The compensation capacitors maintain their charged states continuously during the display phase, providing ongoing compensation for threshold voltage drift. The first capacitor maintains the driving transistor's gate-source voltage, and the second capacitor maintains the light emitting diode's anode voltage, ensuring continuous brightness stability without requiring repeated compensation cycles that would consume additional energy.
Data Source
AI summary
A pixel compensation circuit and an Active Matrix Organic Light Emitting Diode (AMOLED) display apparatus. The circuit includes a data signal writing module, a high voltage signal writing module, a first reference voltage generation module and a second reference voltage writing module; the data signal writing module and the high voltage signal writing module are connected with a first terminal of the capacitor; the first reference voltage generation module is connected with a second terminal of the capacitor and a drain of the driving transistor; a gate of the driving transistor is connected with the second terminal of the capacitor, the drain thereof is connected with an anode of the light emitting device, a source thereof is connected with the second reference voltage writing module, and connected with the high voltage signal writing module; a cathode of the light emitting device is connected with a common ground electrode.