OLED Pixel Storage Capacitor Kickback Voltage Compensation
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Solution Overview
Problem
Active matrix OLED displays face a reduction in luminance due to kickback voltage caused by parasitic capacitance between the control electrode and output electrode of the switching transistor, which affects the output current and overall luminance, especially in pixels with lower luminous efficiency.
Innovation Solution
The OLED display incorporates a storage capacitor with varying channel widths for driving transistors based on luminous efficiency, with the blue pixel having the largest channel width and overlapping control electrodes to enhance capacitance, and a compensation mode to adjust data voltages for uniform luminance across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If the gate-on voltage is changed to gate-off voltage in the switching transistor, then the pixel can be turned off to save power, but a kickback voltage occurs due to parasitic capacitance which decreases the luminance
Solution Approach 1:
The patent applies preliminary anti-action by introducing a compensation transistor that generates a counter-voltage to offset the kickback voltage before it can significantly reduce the luminance. The compensation transistor is activated in response to the switching transistor's state change, creating a preemptive countermeasure that maintains the driving transistor's output current and thus preserves luminance during the transition from gate-on to gate-off voltage.
2Illumination intensity
If the aperture ratio is increased in top-emission OLED to improve light emission, then the luminance is enhanced, but the thickness of the light-emitting layer becomes non-uniform due to height differences between TFT regions and other regions
Solution Approach 1:
The patent applies local quality by making the light-emitting layer's thickness and material composition vary across different regions of the pixel. Specifically, the light-emitting layer is made thicker in the TFT region compared to the emission region, compensating for the height difference caused by the underlying TFT structure. This localized adjustment ensures uniform overall thickness and consistent optical properties across the entire pixel area.
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 solution reduces kickback voltage, maintains higher output current, and ensures consistent luminance across pixels by increasing the capacitance of the storage capacitor and compensating for threshold voltage variations, thereby improving the overall brightness and color uniformity of the OLED display.
Implementation Method 1
a capacitor, connected between the control terminal of the driving transistor and the driving voltage line, when charged through the switching transistor to the threshold voltage of the driving transistor
Implementation Method 2
The injected electrons and holes are combined to form exitons and the exitons emit light as discharge energy
Data Source
AI summary
An organic light emitting diode (OLED) display includes a first pixel including a first light emitting diode, a first driving transistor connected to the first light emitting diode and having a first terminal, a second terminal, and a third terminal, and a first storage capacitor connected between the first terminal and the second terminal of the first driving transistor, and a second pixel including a second light emitting diode, a second driving transistor connected to the second light emitting diode and having a first terminal, a second terminal, and a third terminal, and a second storage capacitor connected between the first terminal and the second terminal of the second driving transistor, wherein the first storage capacitor has a different capacitance than the second storage capacitor.