OLED Pixel Circuit Pre-Driving Threshold Voltage Sampling
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Solution Overview
Problem
Conventional compensation methods for organic light emitting diode (OLED) display devices are insufficient in accurately sampling the threshold voltage of driving transistors within the short horizontal period required for high-resolution and high-speed driving, leading to luminance deviations and spot formation on the screen.
Innovation Solution
The display device incorporates a seventh transistor that performs a pre-driving operation to sample the threshold voltage in advance, allowing for sufficient time to compensate the threshold voltage even in high-speed or high-resolution conditions, ensuring accurate sampling and reduced luminance deviations by applying a pre-driving voltage that is lower than the high potential power supply voltage but higher than the data voltage, with a constant difference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the horizontal period is reduced to increase driving speed and resolution, then productivity is improved, but the threshold voltage sampling time becomes insufficient leading to measurement errors
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage sampling during a dedicated sampling period that occurs before the data writing period. The seventh transistor is activated during this sampling period to charge the sampling capacitor to a voltage level that reflects the threshold voltage, ensuring that the sampling is completed in advance with sufficient time even when the overall horizontal period is shortened for high-speed driving.
2Measurement precision
If the sampling time is extended to improve measurement precision, then threshold voltage sampling accuracy is improved, but the horizontal period increases reducing productivity
Solution Approach 1:
The patent segments the horizontal period into distinct functional periods: a sampling period dedicated to threshold voltage measurement, a data writing period for writing compensated data, and a light emission period. This segmentation allows the sampling operation to be completed efficiently within a limited time window, preventing the sampling time from extending into the data writing period and thus maintaining high driving speed while ensuring accurate threshold voltage sampling.
3Device complexity
If conventional compensation methods are used in high-resolution displays, then device complexity is reduced, but luminance uniformity deteriorates due to insufficient threshold voltage compensation
Solution Approach 1:
The patent uses preliminary action by sampling the threshold voltage in advance during a dedicated sampling period before data writing. The seventh transistor is turned on during this sampling period to charge the sampling capacitor to a voltage level that reflects the threshold voltage, ensuring that the sampling is completed in advance with sufficient time even when the overall horizontal period is shortened for high-speed driving.
Solution Approach 2:
The patent implements a nested structure where the sampling capacitor is integrated within the pixel circuit along with the seventh transistor, forming a compact compensation circuit that does not significantly increase device complexity. The sampling capacitor is nested within the existing pixel structure, sharing space and resources with other circuit elements.
Data Source
AI summary
A display device compensates a threshold voltage Vth of a driving transistor according to a source follower internal compensation method. The threshold voltage Vth of the driving transistor is sampled in advance before one horizontal period H, so that a sufficient time for sampling the threshold voltage Vth of the driving transistor can be obtained even in a high-speed or high-resolution display device. Furthermore, the compensation rate of the internal compensation circuit is improved to reduce luminance deviation between the pixels.