Pixel Circuit Adjustment for Display Visibility in Strong Light
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Solution Overview
Problem
Existing organic EL display devices face challenges in improving visibility in strong external light environments while maintaining display quality and controlling costs, particularly due to variations in transistor characteristics and the need for external light detection systems.
Innovation Solution
The display device incorporates an adjustment circuit with a light receiving circuit and an adjustment capacitor, allowing for internal adjustment of the drive current based on external light intensity without the need for external control systems. This configuration includes a photodiode generating a photocurrent to adjust the light emission intensity and initializes the adjustment node based on an initialization potential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If external light detection systems are used to improve visibility in strong external light environments, then visibility is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the light detection function from external systems and integrates it into the pixel circuit itself using a photodiode. This eliminates the need for separate external light detection systems while maintaining the ability to detect external light intensity and adjust display brightness accordingly.
Solution Approach 2:
The pixel circuit performs self-adjustment of drive current based on external light intensity detected by its own integrated photodiode. The circuit automatically compensates for ambient light conditions without requiring external control systems, achieving self-service functionality that reduces device complexity.
2Illumination intensity
If light detection diode is connected in parallel with drive transistor to adjust light emission intensity, then visibility is improved, but unintended current flows through organic EL element degrading display quality
Solution Approach 1:
The patent uses dynamic control of the photodiode connection through a switching transistor that connects the photodiode to the drive current control node only during specific periods (when the organic EL element is not emitting light). This dynamic switching prevents unintended current flow during light emission while enabling light intensity detection and adjustment during non-emission periods.
Solution Approach 2:
The patent implements periodic adjustment of the drive current based on external light intensity. The photodiode detects light intensity during periods when the organic EL element is off, and the drive current is adjusted in preparation for the next light emission period. This periodic action separates the detection and adjustment functions from the light emission function, preventing interference and maintaining display quality.
3Reliability
If internal compensation method is used to compensate for transistor threshold voltage variations, then display quality is maintained, but additional capacitors and transistors increase device complexity
Solution Approach 1:
The patent makes the photodiode serve multiple functions: it acts as a light detection element for external light intensity measurement, and simultaneously functions as part of the threshold voltage compensation mechanism by generating photocurrent that adjusts the drive current control node potential. This multi-functionality reduces the need for separate compensation components, lowering device complexity while maintaining display quality.
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 enhances visibility in strong external light environments by adjusting the drive current accordingly, without degrading display quality or increasing costs, as it eliminates the need for external light detection systems and unintended current flow through the organic EL element.
Implementation Method 1
a light receiving circuit including a light receiving element and connected to the light emission intensity adjustment node, the light receiving circuit being configured to generate a photocurrent depending on intensity of light incident on the light receiving element
Data Source
AI summary
Regarding a display device using a display element driven by a current, visibility in an environment where external light is strong is improved while suppressing deterioration in display quality and an increase in cost.An adjustment circuit (22) and an adjustment capacitor (Cp) for adjusting an amount of drive currents are provided for each one pixel circuit (20) or every plural pixel circuits (20). As for the adjustment capacitor (Cp), a first electrode is connected to a drive current control node (NG) connected to a control terminal of a drive transistor (T4), and a second electrode is connected to a light emission intensity adjustment node (NP) in the adjustment circuit (22). The adjustment circuit (22) includes a photodiode (220) and a photocurrent control transistor (T8) provided in series with each other between a high-level power supply line and the light emission intensity adjustment node (NP), and a third initialization transistor (T9) provided between an initialization power supply line and the light emission intensity adjustment node (NP).