Organic EL Display Current Modulation for Luminance Stability
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Solution Overview
Problem
Display apparatuses using light-emitting elements face degradation issues due to increased current density and temperature variations, leading to reduced luminance and image quality, with existing techniques failing to effectively delay degradation and maintain image quality.
Innovation Solution
A display apparatus with a pixel array, data signal drive circuit, scanning signal drive circuit, and current source that modulates current within each frame period and controls gray scale levels based on average luminance to reduce luminance changes and delay degradation, using a cathode potential control circuit to measure and adjust current and voltage accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If current density of light-emitting elements is increased to improve display luminance, then peak luminance is enhanced, but degradation of light-emitting elements accelerates
Solution Approach 1:
The patent applies periodic action by modulating the current supplied to light-emitting elements within each frame period. The current is increased during specific time intervals to achieve high peak luminance when needed (e.g., for white or high gray scale levels), then reduced or interrupted during other intervals to allow degradation recovery. This periodic modulation enables the display to achieve high peak luminance levels while reducing overall degradation accumulation compared to continuous high current operation.
2Stability of the object's composition
If current density is increased to maintain luminance during temperature variations, then luminance stability is improved, but degradation accelerates
Solution Approach 1:
The patent employs feedback mechanisms where the display control circuit monitors the average luminance level of the display unit and adjusts the current supplied to light-emitting elements accordingly. When temperature variations cause luminance to deviate from desired levels, the feedback control modifies the current in real-time to compensate, maintaining luminance stability without requiring continuously high current that would accelerate degradation.
3Illumination intensity
If voltage is increased to compensate for luminance reduction due to degradation, then luminance is maintained, but degradation is accelerated
Solution Approach 1:
The patent applies dynamics by making the current supply to light-emitting elements time-dependent and variable within each frame period rather than static. The current level is dynamically adjusted based on the display requirements - higher current is supplied only when high luminance is needed for specific gray scale levels or time intervals, while lower current is used during other periods. This dynamic approach maintains necessary luminance levels while significantly reducing the cumulative degradation effect compared to continuously high voltage operation.
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 approach enhances peak luminance for high gray scale levels, reduces luminance for low gray scale levels, improves contrast and image quality, and extends the life of light-emitting elements while minimizing luminance changes due to temperature variations.
Implementation Method 1
Light-emitting (or self-luminous) elements have the characteristic that the luminance of light emitted from them is proportional to the amount of current flowing through them
Data Source
AI summary
The present invention comprises: a display unit having a plurality of pixels arranged therein, each pixel including an organic EL element 24, a switching TFT, and a drive TFT; a data signal drive circuit for receiving image data for each frame period and outputting an image signal based on the image data; a scanning signal drive circuit for outputting a scanning signal for controlling a timing at which the switching element of each of the plurality of pixels receives the image signal; and a current source (a light emission power supply unit and a cathode potential control circuit together) for outputting a current supplied to the light emitting unit of each of the plurality of pixels through its drive element; wherein the current source modulates the value of the output current within each frame period.