Organic Light Emitting Display Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
As the resolution of display devices increases, it becomes challenging to sufficiently compensate for the variation in threshold voltages of pixel driving transistors in organic light emitting display devices, particularly during shorter horizontal periods.
Innovation Solution
The organic light emitting display device employs a specific driving method that divides a frame period into multiple phases, including initialization, threshold voltage storage, and sequential data signal supply, using a combination of transistors and capacitors to stabilize voltage and ensure consistent emission across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the resolution of display is increased, then the image quality is improved, but the horizontal period becomes shorter making it difficult to sufficiently compensate for threshold voltage variation
Solution Approach 1:
The pixel circuit is divided into multiple transistors (first transistor for current control, second transistor for data signal input, third transistor for threshold voltage compensation) and capacitors (first capacitor for threshold voltage storage, second capacitor for data signal storage). This segmentation allows each component to perform its specific function independently, enabling sufficient threshold voltage compensation even with shortened horizontal periods in high-resolution displays.
Solution Approach 2:
The third transistor is turned on before the second transistor to pre-charge the first capacitor with the threshold voltage of the driving transistor. This preliminary action ensures that the threshold voltage is stored in advance in the first capacitor, allowing for accurate compensation when the pixel is driven, even when the overall horizontal period is shortened due to high resolution requirements.
2Measurement precision
If multiple transistors and capacitors are added for threshold voltage compensation, then the compensation accuracy is improved, but the device complexity increases
Solution Approach 1:
The first capacitor serves multiple functions: it stores the threshold voltage of the driving transistor for compensation purposes and also maintains the voltage level during different operating periods (first, second, and third periods). This multi-functionality reduces the need for additional dedicated compensation components, thereby limiting the increase in device complexity while maintaining compensation accuracy.
Solution Approach 2:
The compensation mechanism is localized to specific nodes within the pixel circuit. The first capacitor is connected between the first node and the second power source, specifically targeting the storage of threshold voltage at the gate of the driving transistor. This localized approach allows precise compensation without requiring complex circuitry across the entire pixel, thus balancing accuracy with manageable complexity.
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
This approach allows for stable compensation of threshold voltages, enabling the creation of high-resolution display panels by ensuring consistent pixel operation and efficient light emission.
Implementation Method 1
An organic light emitting display generates images based on light emitted from pixels that include organic light emitting diodes. Each organic light emitting diode emits based on a recombination of electrons and holes in an organic layer.
Data Source
AI summary
An organic light emitting display device includes a plurality of pixels. A pixel on an ith horizontal line includes a first transistor coupled between a first power source and a first node and having a gate electrode coupled to a second node. An organic light emitting diode is coupled between the first node and a second power source. A second transistor is coupled between the second and third nodes and is turned on when a first scan signal is supplied to an ith first scan line. A third transistor is coupled between the third and first nodes. A first capacitor is coupled between an ith control line and the second node. A second capacitor is coupled between the third node and a data line. The pixels are simultaneously driven during first, second, and third periods of a frame period and sequentially driven during a fourth period of the frame period.