Scan Driver Reset Circuit for Display Luminance Stability
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Solution Overview
Problem
Display devices with variable drive frequencies face challenges in maintaining consistent gray levels and luminance due to variations in electrical characteristics of drive transistors, leading to potential image flicker and luminance changes, especially when frame rates differ non-integally.
Innovation Solution
A display device with a scan driver that includes multiple stages, where the first node of each stage is reset periodically using a separate reset signal during the blank period, ensuring a consistent light emission-off period even when frame rates vary, and the reset cycle is maintained constant regardless of changes in drive frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If all stages are reset by a scan start signal at every frame start, then the reset operation is simple to implement, but the light emission-off period is not sufficiently obtained and luminance stability deteriorates
Solution Approach 1:
The reset operation is segmented into two distinct phases: a first reset phase using the scan start signal for initial reset, and a second reset phase using a dedicated reset signal for complete reset. This segmentation allows the light emission-off period to be sufficiently obtained while maintaining operational simplicity through structured reset sequencing.
2Adaptability or versatility
If frame rate is varied to adapt to different rendering times, then the display can handle variable image processing requirements, but the vertical blank period varies causing non-constant reset periods and transistor deterioration
Solution Approach 1:
The reset operation is performed preliminarily at a fixed timing within the blank period using the scan start signal, and then a second reset is performed using a dedicated reset signal. This preliminary action ensures that the reset cycle remains constant regardless of frame rate variations, protecting transistors from deterioration while maintaining frame rate adaptability.
3Illumination intensity
If additional light emission-off period is inserted into blank period when driven at lower frame rate, then luminance decrease is prevented, but the reset cycle becomes non-constant and transistor deterioration increases
Solution Approach 1:
The reset operation is performed periodically at fixed intervals within the blank period using the scan start signal, followed by a second periodic reset using the dedicated reset signal. This periodic action maintains a constant reset cycle regardless of frame rate or additional light emission-off period insertions, preventing transistor deterioration while ensuring luminance stability.
Data Source
AI summary
A display device includes pixels connected to scan lines, sensing lines, readout lines, and data lines; a scan driver including stages to supply a scan signal and a sensing signal to the scan lines and the sensing lines; a data driver which supplies a data signal to the data lines; a timing controller which divides one frame into an active period including a scan period in which the data signal is supplied to the data lines and a display period in which the pixels emit light in response to the data signal, and a blank period including a sensing period in which electrical characteristics of the pixels are detected and a reset period in which the stages are reset; and a compensator which generates a compensation value for compensating for deterioration of the pixels based on sensing values provided from the readout lines during the sensing period.