Display Device Threshold Voltage Drift Correction
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Solution Overview
Problem
Display devices with organic EL devices face image quality deterioration and gradation issues due to variations in threshold voltage and mobility over time, leading to color heterogeneity and inability to set gradations effectively.
Innovation Solution
A display device and driving method where the signal level of the write signal is set on a shorter time period side during non-emission times, correcting the threshold voltage and mobility dispersions by adjusting the signal level for entire or partial time periods, ensuring the organic EL device is driven efficiently and maintaining image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the write signal level is maintained at a normal level for the entire non-emission time period, then the writing transistor can be fully turned on for complete signal writing, but the threshold voltage of the writing transistor varies with age leading to image quality deterioration and gradation issues
Solution Approach 1:
The write signal is applied periodically with different signal levels during different phases of the non-emission time period. The signal level is changed based on the elapsed time, creating a periodic pattern that addresses threshold voltage variation while maintaining reliable signal writing throughout the display device's operation.
Solution Approach 2:
The signal level parameter of the write signal is dynamically changed during the non-emission time period based on elapsed time. By adjusting the signal level (e.g., from first level to second level), the patent compensates for threshold voltage drift and prevents image quality deterioration without requiring additional circuit components.
2Stability of the object's composition
If the write signal level is changed frequently to correct threshold voltage, then threshold voltage variation can be compensated, but the signal writing time is reduced affecting display performance
Solution Approach 1:
The write signal operates in periodic cycles, utilizing the non-emission time period (when the light emitting device is off) to apply corrected signal levels. This periodic approach allows threshold voltage compensation without interfering with the emission period, thus maintaining display performance while addressing stability issues.
Solution Approach 2:
The threshold voltage compensation is performed in advance during the non-emission time period before the next emission cycle begins. By preparing the writing transistor with the appropriate signal level during the off period, the patent ensures optimal performance during the emission period without losing display time.
3Ease of operation
If the entire non-emission time period is used for signal writing, then complete signal level setting is achieved, but threshold voltage variation accumulates causing image quality deterioration
Solution Approach 1:
The non-emission time period is segmented into multiple phases based on elapsed time. Different signal levels are applied to different segments (e.g., first half vs. second half), allowing complete signal writing while simultaneously addressing threshold voltage variation. This segmentation enables both comprehensive signal setting and quality maintenance.
Solution Approach 2:
The signal level parameter is changed at specific time points within the non-emission period. By transitioning from a first signal level to a second signal level based on elapsed time, the patent achieves both complete signal writing and threshold voltage compensation, ensuring image quality consistency throughout operation.
Data Source
AI summary
A display device includes a display portion formed by disposing pixels in matrix, in which the pixel includes: a light emitting element; a signal level holding capacitor; a writing transistor for receiving a write signal from the vertical drive circuit, and being turned ON/OFF by the write signal, thereby setting a voltage across the terminals of the signal level holding capacitor at a signal level on a signal line; and a driving transistor for driving the light emitting device; and the vertical drive circuit sets a signal level of the write signal for an entire or partial time period of a time period for which the drive for the light emitting device is not influenced in a non-emission time period for which light emission of the light emitting device is stopped at a signal level of the write signal on a shorter time period side in other time periods.