OLED Pixel Circuit Threshold Voltage Compensation Segmentation
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Solution Overview
Problem
Organic light emitting display (OLED) devices experience non-uniform luminance due to hysteresis characteristics of driving transistors, which is exacerbated when threshold voltage compensation and data programming operations are performed simultaneously within a short time period.
Innovation Solution
A method and pixel circuit design that separates threshold voltage compensating and data programming operations for driving transistors, initializing the gate electrodes with an initial value before data programming, using a compensation capacitor to apply data voltage indirectly, and ensuring sufficient threshold voltage compensation time, thereby improving luminance uniformity and contrast ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If threshold voltage compensation and data programming operations are performed simultaneously, then data programming speed is improved, but luminance uniformity deteriorates due to insufficient compensation time
Solution Approach 1:
The patent segments the previously simultaneous operations into distinct time phases: a first phase for threshold voltage compensation and a second phase for data programming. This temporal segmentation allows each operation to complete fully without interfering with the other, resolving the contradiction between speed and precision by ensuring sufficient compensation time while maintaining efficient data programming.
Solution Approach 2:
The patent applies preliminary action by performing threshold voltage compensation before data programming. The gate electrode is initialized to a reference voltage that accounts for the transistor's threshold voltage in advance, ensuring that when data programming occurs, the transistor is already in the correct initial state. This preliminary compensation action prevents luminance uniformity issues while enabling fast data programming.
2Manufacturing precision
If threshold voltage compensation time is extended to improve luminance uniformity, then manufacturing precision is improved, but data programming speed deteriorates
Solution Approach 1:
By dividing the operation sequence into distinct compensation and programming phases, the patent achieves complete threshold voltage compensation without extending the overall frame time. The segmentation allows the compensation to occur fully in the first phase, then data programming proceeds rapidly in the second phase, maintaining both luminance uniformity and programming speed.
Solution Approach 2:
The patent changes the voltage parameter at the gate electrode from a previous frame's data voltage to a reference voltage during the compensation phase. This parameter change enables proper threshold voltage compensation. After compensation, the parameter changes again to the new data voltage for programming, allowing both precise compensation and fast programming to coexist.
Data Source
AI summary
A method of driving a pixel circuit includes initializing a driving transistor and a storage capacitor by simultaneously applying an initialization voltage and a first power voltage to a gate electrode of the driving transistor and the storage capacitor, respectively, diode-coupling the driving transistor, applying a data voltage to the storage capacitor, applying the data voltage to the gate electrode of the driving transistor by a coupling of a compensation capacitor coupled between the gate electrode of the driving transistor and the storage capacitor, and applying a current corresponding to the first power voltage and the data voltage to an organic light emitting diode that is coupled to the driving transistor.