OLED Pixel Circuit On-Bias Stress and Row-Dependent Gate Drive
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Solution Overview
Problem
Organic light-emitting diode (OLED) displays face issues with brightness nonuniformity due to variations in threshold voltages of drive transistors caused by operating history effects, and capacitive loading variations in non-rectangular shaped displays.
Innovation Solution
The display employs an array of pixels with seven transistors and a capacitor, where first and second emission enable transistors are coupled in series with a drive transistor and a light-emitting diode. Individual control of these emission enable transistors allows for on-bias stress application to the drive transistor, and gate drive circuits generate row-location-dependent gate line signals to counteract capacitive loading effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If drive transistors are used to control current flow through light-emitting diodes, then display functionality is achieved, but threshold voltage variations due to operating history effects cause brightness nonuniformity
Solution Approach 1:
The patent applies on-bias stress to drive transistors during specific time periods (such as during emission enable periods or data writing periods) to preemptively compensate for threshold voltage shifts before they affect display brightness. This preliminary action stabilizes the transistor characteristics and ensures uniform brightness across the display.
Solution Approach 2:
The patent dynamically adjusts the stress voltage applied to drive transistors based on their operating history and accumulated stress levels. By changing the stress parameter (voltage magnitude and duration) according to transistor state, the system compensates for threshold voltage drift and maintains brightness uniformity.
2Adaptability or versatility
If non-rectangular display shapes are used to achieve design flexibility, then adaptability is improved, but capacitive loading variations cause brightness nonuniformity
Solution Approach 1:
The patent applies different stress conditions to drive transistors in different regions of the display based on their specific capacitive loading characteristics. Transistors in rows with higher capacitive loading receive different stress parameters than those in rows with lower loading, locally compensating for variations and achieving uniform brightness across the entire non-rectangular display.
3Reliability
If emission enable transistors are individually controlled to apply on-bias stress, then brightness uniformity is improved, but device complexity increases
Solution Approach 1:
The emission enable transistors serve multiple functions: they control the emission timing of light-emitting diodes and simultaneously provide a pathway for applying on-bias stress to drive transistors. This multi-functionality allows the same control circuitry to achieve both display timing control and transistor stress compensation without adding separate control mechanisms.
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 solution effectively minimizes brightness variations across the display by applying on-bias stress to drive transistors and adjusting gate line signals based on row-dependent capacitive loading, resulting in improved brightness uniformity.
Implementation Method 1
Each pixel includes a light-emitting diode and thin-film transistors for controlling application of a signal to the light-emitting diode to produce light
Data Source
AI summary
A display may have an array of pixels. Display driver circuitry may supply data and control signals to the pixels. Each pixel may have seven transistors, a capacitor, and a light-emitting diode such as an organic light-emitting diode. The seven transistors may receive control signals using horizontal control lines. Each pixel may have first and second emission enable transistors that are coupled in series with a drive transistor and the light-emitting diode of that pixel. The first and second emission enable transistors may be coupled to a common control line or may be separately controlled so that on-bias stress can be effectively applied to the drive transistor. The display driver circuitry may have gate driver circuits that provide different gate line signals to different rows of pixels within the display. Different rows may also have different gate driver strengths and different supplemental gate line loading structures.