Display Device Driving Voltage Control for Parasitic Capacitance Charging
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Solution Overview
Problem
Organic light emitting display devices face delays in light emission and low-gradation stains due to increased charging time of parasitic capacitance when emitting light with low-gradation luminance, as the driving current is small, causing pixels to fail in expressing intended gradations.
Innovation Solution
The implementation of a display device with a first driving voltage line and a second driving voltage line, where the first driving voltage is changed from a high-level to a low-level voltage during an initialization period, and the second driving voltage remains at a low level, reducing the impact of parasitic capacitance on the light emitting element's charging time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the driving current is reduced to achieve low-gradation luminance, then the luminance is reduced, but the charging time of parasitic capacitance increases causing light emission delay and gradation loss
Solution Approach 1:
The patent applies preliminary action by changing the driving voltage to a low level during the initialization period before the light emitting element is driven. This preliminary voltage adjustment reduces the parasitic capacitance charging time requirement, ensuring that when the element is subsequently driven at low currents for low-gradation luminance, the timing issues are already resolved. The initialization phase prepares the system in advance to handle the timing constraints of low-current operation.
2Use of energy by moving object
If the driving current is small for low-gradation luminance, then energy consumption is reduced, but the pixel fails to express the intended gradation accurately
Solution Approach 1:
The patent employs parameter changes by adjusting the driving voltage level based on the operation phase. During the initialization period, the driving voltage is changed to a low level, which modifies the electrical parameters of the light emitting element and reduces the time constant for parasitic capacitance charging. This parameter adjustment enables accurate gradation expression even when operating at low driving currents during the display phase, as the timing characteristics are optimized in advance.
Data Source
AI summary
A display device includes a data line to which a data voltage is applied, a first driving voltage line to which a first driving voltage is applied, a second driving voltage line to which a second driving voltage is applied, and a pixel connected to the first and second driving voltage lines. The pixel includes a first transistor to control a driving current according to a voltage applied to a first node, a light emitting element between the first transistor and the first driving voltage line, and a capacitor between the first node and the second driving voltage line. The first driving voltage has a first high-level voltage during a first initialization period, the first driving voltage has a first mid-level voltage lower than the first high level voltage during a threshold-voltage-storage period, and the first driving voltage has a first low-level voltage during a second initialization period.