AMOLED Pixel Circuit Parasitic Capacitance Kickback Voltage
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Solution Overview
Problem
The response characteristics of active matrix organic light emitting display (AMOLED) pixels are adversely affected by parasitic capacitance, leading to uneven image quality due to voltage fluctuations caused by kickback voltage generated between the storage capacitor and anode electrode, resulting in degraded image quality.
Innovation Solution
Incorporating a reset transistor that supplies a constant reset voltage to the anode electrode of the organic light emitting diode during an initialization period, maintaining the kickback voltage constant for each gray level, thereby stabilizing the response characteristics and ensuring uniform image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a top-emission type AMOLED structure is used with overlapping pixel circuit and organic light emitting diode, then device integration is achieved, but parasitic capacitance is generated between storage capacitor and anode electrode causing kickback voltage
Solution Approach 1:
The patent extracts the harmful parasitic capacitance effect by separating the storage capacitor into two distinct capacitors: a first capacitor coupled to the anode electrode and a second capacitor coupled to the gate electrode of the driving transistor. This separation removes the direct parasitic coupling path between the storage function and the anode electrode, thereby eliminating the kickback voltage problem while maintaining the integrated OLED structure.
Solution Approach 2:
The storage capacitor is segmented into two functional capacitors with distinct roles. The first capacitor handles the anode electrode coupling and is initialized to a reference voltage, while the second capacitor handles the gate electrode coupling and stores the driving voltage. This segmentation isolates the parasitic capacitance effects to manageable components and prevents their harmful interaction.
2Device complexity
If parasitic capacitance is present between storage capacitor and anode electrode, then device structure is simplified, but voltage fluctuation occurs at gate electrode node causing uneven image quality
Solution Approach 1:
The harmful voltage fluctuation caused by parasitic capacitance is extracted and isolated to the first capacitor, which is separately initialized to a reference voltage. This prevents the fluctuation from propagating to the gate electrode node, ensuring stable driving voltage and uniform image quality across all pixels.
Solution Approach 2:
The first capacitor acts as an intermediary element between the anode electrode and the rest of the pixel circuit. By initializing this intermediary capacitor to a stable reference voltage, the harmful effects of parasitic capacitance are contained and isolated, preventing them from affecting the gate electrode node and subsequent image quality.
3Reliability
If kickback voltage is generated by parasitic capacitance, then previous frame gray level affects current frame display, but adding initialization transistor and capacitor increases device complexity
Solution Approach 1:
The first capacitor is pre-initialized to a reference voltage during a initialization period before the display period. This preliminary action establishes a stable baseline voltage that prevents kickback voltage from affecting the gate electrode node during subsequent frame transitions, ensuring consistent display quality regardless of previous frame content.
Solution Approach 2:
The pixel circuit is segmented into distinct initialization and display functions. The first capacitor and its associated initialization transistor handle the reference voltage establishment, while the second capacitor and driving transistor handle the image display. This functional segmentation isolates the initialization overhead to specific components, making the added complexity manageable and targeted.
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 improves the response characteristics of the pixels by maintaining a constant kickback voltage across all gray levels, preventing luminance variations and ensuring a uniform image quality across frames.
Implementation Method 1
an organic light emitting diode (OLED) coupled between a first power and a second power
Data Source
AI summary
A pixel capable of improving response characteristics and displaying an image having a uniform image quality, and an organic light emitting display device using the same. The pixel includes an organic light emitting diode coupled between first power and second power; a pixel circuit coupled between the first power and the organic light emitting diode for supplying a driving current to the organic light emitting diode; and a first transistor for supplying a reset voltage to an anode electrode of the organic light emitting diode during a first period when a previous scan signal is supplied to a previous scan line.