Dynamic Storage Capacitance for OLED Threshold Sensing
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Solution Overview
Problem
In organic light emitting display panels, the accuracy of sensing the threshold voltage of the driving transistor is reduced due to the increased time required for charging the source voltage to the target voltage, especially when a large storage capacitance is used to minimize noise and enhance data voltage holding, which conflicts with the need for quick sampling operations.
Innovation Solution
The storage capacitance is dynamically varied based on a storage signal, with a higher capacitance during image display and a lower capacitance during the sampling period to enhance the accuracy of threshold voltage sensing, using a capacitor unit connected between the gate and source of the driving transistor, comprising first and second storage capacitors and a storage transistor that controls the capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large storage capacitance is used to minimize noise and enhance data voltage holding, then noise characteristic and data voltage holding are improved, but the time required for charging the source voltage increases, reducing sampling operation accuracy
Solution Approach 1:
The storage capacitance is changed from a fixed value to a dynamically adjustable value. During the sampling operation, the storage capacitance is set to a first (smaller) value to enable fast charging and accurate threshold voltage sensing. During the emission operation, the storage capacitance is set to a second (larger) value to minimize noise and hold data voltage. This dynamic adjustment resolves the contradiction by optimizing capacitance for each operational phase.
Solution Approach 2:
The capacitance parameter of the storage capacitor is varied based on operational requirements. By changing the capacitance value from a constant to a variable parameter that adapts to different operation modes (sampling vs. emission), the system achieves both fast sampling response and low noise performance without compromise.
2Stability of the object's composition
If a large storage capacitance is used to enhance data voltage holding characteristic, then data voltage holding is improved, but the time taken for source voltage to reach target voltage increases, reducing productivity
Solution Approach 1:
The storage capacitance value is dynamically switched between two states: a smaller value during sampling operations to enable fast voltage changes and high productivity, and a larger value during emission operations to provide stable data voltage holding. This temporal separation of capacitance values resolves the contradiction between speed and stability.
Solution Approach 2:
The storage capacitance is periodically adjusted according to the operation cycle. During the sampling period, the capacitance is set to a smaller value for fast response. During the emission period, the capacitance is set to a larger value for stable holding. This periodic switching aligns with the display refresh cycle and resolves the speed-stability trade-off.
Data Source
AI summary
Disclosed are an organic light emitting display panel and an organic light emitting display device including the same, which decrease a level of a storage capacitance in a sampling period in which a threshold voltage of a driving transistor is sensed, and increase a level of the storage capacitance in an emission period for image display.