Flat Display Device Alternating Sub-Pixel Driving Periods
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Solution Overview
Problem
Conventional flat display devices experience threshold voltage shifts in driving transistors during prolonged white image rendering, leading to luminance degradation and reliability issues due to negative bias stress, with limited compensation ranges.
Innovation Solution
The implementation of a flat display device that alternates between two driving periods for sub-pixels, using different white unit data to manage threshold voltage shifts, ensuring that the threshold voltage of driving transistors is maintained within a stable range by adjusting the emission periods of red, green, and blue sub-pixels in conjunction with the white sub-pixel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a white image is rendered for a lengthened period of time using conventional four-color flat display devices, then the white sub-pixel and two of the red, green, and blue sub-pixels are continuously driven to maintain display function, but the threshold voltages of driving transistors of the non-driving sub-pixels are shifted in the negative direction due to stress applied to the driving transistors, leading to luminance increase and reliability degradation
Solution Approach 1:
The patent implements periodic switching between two driving periods (first and second driving periods) for displaying white images. During the first driving period, the white sub-pixel and two color sub-pixels are driven while the remaining color sub-pixel is non-driving. During the second driving period, the white sub-pixel and the previously non-driving color sub-pixel are driven while the other two color sub-pixels are non-driving. This periodic alternation prevents continuous stress on the same transistor, thereby preventing threshold voltage shifts and maintaining reliability over extended display durations.
2Measurement precision
If data voltage is shifted to compensate for the shifted levels of the threshold voltages, then the threshold voltage variation is partially compensated, but the range of compensation is limited and luminance may be increased when threshold voltages are continuously shifted beyond the compensation range
Solution Approach 1:
The patent applies preliminary action by proactively switching between different driving periods before threshold voltage shifts can accumulate beyond the compensation range. Instead of waiting for threshold voltage drift to occur and then attempting compensation, the system preemptively alternates which sub-pixels are driving and which are non-driving, thereby preventing the stress conditions that cause threshold voltage shifts in the first place. This eliminates the need for extensive compensation ranges.
3Illumination intensity
If the threshold voltages are continuously shifted in the negative direction beyond the compensation range, then the threshold voltage stability is lost, but luminance is increased and degradation of reliability occurs
Solution Approach 1:
The patent uses periodic switching between two driving periods to ensure that no single color sub-pixel's driving transistor is continuously stressed. By alternating which sub-pixel is non-driving (and thus which transistor bears the stress), the system maintains threshold voltage stability within the compensation range, preventing the runaway luminance increase and reliability degradation that would occur if threshold voltages shifted continuously beyond compensation capabilities.
Data Source
Figure 1
Figure 2~3
Figure 4A~4B
AI summary
A flat display device includes a display panel. The display panel includes a unit pixel, the unit pixel having a red sub-pixel, a green sub-pixel, a blue sub-pixel, and a white sub-pixel. The flat display device further includes a panel driving unit to drive the flat panel in a first driving period and a second driving period in an alternating manner to display a white image on the unit pixel. The panel driving unit generates first white unit data, to enable two of the red, green, and blue sub-pixels and the white sub-pixel to be driven in the first driving period. The panel driving unit generates second white unit data, to enable three of the sub-pixels, which include the sub-pixel not driven in the first driving period, to be driven in the second driving period.