OLED Pixel Circuit Dynamic Reference Voltage Contrast Ratio
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Solution Overview
Problem
Existing organic light emitting display devices face reduced contrast ratios due to undesired emission of light during low gray scale realization, leading to luminance deviations and shortened service life, and internal and external compensation technologies compromise aperture ratios.
Innovation Solution
An organic light emitting display device with a pixel circuit that adjusts data voltages based on varying reference voltages, shared among multiple pixels, to prevent light emission during data charging periods, thereby enhancing contrast ratio and aperture ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed reference voltage is applied to the gate electrode of the driving transistor, then the pixel circuit can be simplified, but light emission occurs during data charging periods when data voltage exceeds the organic light emitting device threshold voltage, reducing contrast ratio
Solution Approach 1:
The reference voltage is changed from a fixed value to a dynamically variable value that changes according to the display data. The data driver varies the reference voltage supplied to the gate electrode based on the gray level being displayed, ensuring that the voltage difference between gate and source electrodes never exceeds the organic light emitting device threshold voltage during data charging, thereby preventing unwanted light emission while maintaining circuit simplicity
Solution Approach 2:
The reference voltage parameter is changed from a constant fixed value to a variable value that adapts to different display conditions. By adjusting the reference voltage level according to the display data (gray level), the system prevents the gate-source voltage difference from exceeding the threshold voltage of the organic light emitting device, thus eliminating contrast ratio degradation without adding complex circuitry
2Reliability
If internal compensation technology is used to compensate for driving transistor characteristic changes, then pixel characteristic uniformity is improved, but the aperture ratio is reduced due to added compensation transistors and capacitors
Solution Approach 1:
The compensation function is extracted from the pixel-level circuit and moved to the data driver circuit. Instead of adding compensation transistors and capacitors within each pixel, the system uses a data driver that varies the reference voltage globally based on display data, achieving compensation for driving transistor characteristic changes without occupying pixel area
Solution Approach 2:
The data driver acts as an intermediary that provides compensation by adjusting the reference voltage before it reaches the pixel circuit. This external compensation mechanism mediates between the data voltage and the gate electrode, ensuring proper voltage levels without requiring additional components within the pixel structure
3Ease of operation
If data voltage is applied directly to the source electrode during data charging, then the pixel circuit operation is simplified, but undesired light emission occurs when data voltage exceeds the threshold voltage of the organic light emitting device
Solution Approach 1:
The reference voltage supplied to the gate electrode is made dynamic and variable according to the display data. This dynamic adjustment ensures that even when data voltage is applied directly to the source electrode during data charging, the gate-source voltage difference never exceeds the threshold voltage of the organic light emitting device, preventing undesired light emission while maintaining simplified circuit operation
Solution Approach 2:
The system takes preliminary action by adjusting the reference voltage before data charging occurs. By pre-setting the reference voltage level based on the display data, the system prevents the gate-source voltage difference from exceeding the threshold voltage during subsequent data charging, thereby preemptively avoiding undesired light emission
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents light emission during data charging periods, improving contrast ratio and increasing aperture ratio by dynamically adjusting data voltages according to display data, thus extending the service life and enhancing image quality.
Implementation Method 1
an organic light emitting device which emits light with a data current
Data Source
AI summary
Discussed is an organic light emitting display device. The organic light emitting display device in one embodiment includes a plurality of pixels configured to each include an organic light emitting device which emits light with a data current, and a pixel circuit that includes a driving transistor which supplies the data current, which is based on a difference voltage between a data voltage and a reference voltage, to the organic light emitting device, a plurality of data lines configured to respectively supply a plurality of the data voltages to the plurality of pixels, a plurality of gate lines configured to supply a gate signal to the pixels, and a plurality of reference lines connected to at least one of the pixels, and configured to supply the reference voltage to the connected pixel. The reference voltage is varied according to data of a pixel connected to a corresponding reference line.