Pixel Circuit Reset Mechanism for Flicker Suppression in Organic EL Displays
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Solution Overview
Problem
Existing organic EL display devices experience flicker during pause driving due to hysteresis characteristics in thin-film transistors, and methods to suppress flicker often increase power consumption.
Innovation Solution
A pixel circuit design that includes a drive transistor, a drive current control node, a holding capacitor, and specific transistors for threshold voltage compensation and light-emission control, along with a reset circuit that applies an off-voltage followed by an initialization voltage to the drive current control node during refresh frame periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If pause driving is implemented to reduce power consumption, then power consumption is reduced, but flicker occurs due to hysteresis characteristics in the drive transistor
Solution Approach 1:
The invention applies preliminary action by providing an off-voltage to the drive transistor before the light-emission period during refresh frame periods. This preliminary voltage application prevents hole-trap accumulation that would otherwise cause luminance variation and flicker during pause driving, while still allowing power consumption reduction during non-refresh frame periods.
Solution Approach 2:
The invention implements periodic action by alternately applying off-voltage during refresh frame periods and maintaining normal operation during non-refresh frame periods. This periodic voltage application pattern synchronizes with the display refresh rate to prevent flicker while enabling pause driving for power consumption reduction.
2Object-generated harmful factors
If periodic turn-off configuration is used to suppress flicker, then flicker is reduced, but power consumption increases during pause period
Solution Approach 1:
Instead of continuously turning off the organic EL element during pause period, the invention applies preliminary off-voltage only during refresh frame periods to prevent flicker, while allowing the element to remain on during non-refresh frame periods, thereby reducing power consumption compared to continuous turn-off approaches.
3Device complexity
If drive transistor hysteresis is not compensated, then circuit operation is simple, but luminance variations occur degrading display quality
Solution Approach 1:
The invention addresses drive transistor hysteresis by applying preliminary off-voltage during refresh frame periods, which prevents hole-trap accumulation before light emission. This preliminary action compensates for hysteresis effects and eliminates luminance variations without requiring complex compensation circuits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively suppresses flicker by maintaining a constant hole-trap occupancy in the drive transistor channel during light-emission periods, while also preventing an increase in power consumption during pause periods.
Implementation Method 1
an organic EL element configured to emit light at luminance determined based on an amount of a drive current supplied to the organic EL element
Implementation Method 2
since a thin-film transistor serving as a drive transistor in a pixel circuit has hysteresis characteristics, when pause driving is performed, flicker is still visually recognized
Data Source
AI summary
Regarding a display device that uses display elements driven by current, occurrence of flicker upon pause driving is suppressed while an increase in power consumption is suppressed. In a period, during which supply of a drive current to an organic EL element is stopped, in a refresh frame period (RF) included in a driving period, before a writing period (14) during which a data voltage is provided to the control terminal of the drive transistor, a reset circuit provided in a pixel circuit provides an off-voltage that brings a drive transistor into off state to a control terminal of the drive transistor, and then provides an initialization voltage that brings the drive transistor into on state to the control terminal of the drive transistor.