Electroluminescent Display Driver Current Compensation
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Solution Overview
Problem
Active matrix electroluminescent displays, such as OLEDs, face issues with voltage drops along power lines due to finite resistance, leading to luminance variations and undesirable imaging artifacts, which limit the size and luminance of displays and result in reduced image quality.
Innovation Solution
An electroluminescent display system that includes a display driver analyzing the input signal to estimate current variations along power lines and generating a converted image signal to limit these variations, using normalization constants and correction factors to reduce unintended current draw and luminance differences between neighboring regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the power lines are made longer to enable larger displays, then the display size increases, but the resistance of the power lines increases leading to larger IR drops and luminance variations
Solution Approach 1:
The display driver pre-calculates the current that would be drawn by each pixel before actually driving the display. Based on these pre-calculated current values, the driver generates correction factors that compensate for the expected IR drops. This preliminary calculation and correction approach allows the system to anticipate and counteract the voltage drops before they affect the luminance uniformity across the display.
2Illumination intensity
If the current to light emitting elements is increased to produce brighter displays, then the luminance increases, but the IR drop along power lines increases causing larger luminance variations and imaging artifacts
Solution Approach 1:
The display driver measures or calculates the actual current being drawn by the display and uses this feedback to generate correction factors. These correction factors are then applied to the pixel data to compensate for the IR drops. This feedback mechanism allows the system to dynamically adjust for voltage drops and maintain luminance uniformity even when displaying high-luminance images that draw significant current.
Solution Approach 2:
The system changes the voltage parameters applied to different regions of the display based on the calculated current draw. By adjusting the voltage compensation dynamically according to the actual operating conditions and current levels, the system maintains luminance uniformity across the display while allowing for high overall luminance output.
3Manufacturing precision
If the resistance of power lines is reduced to minimize IR drops, then the luminance uniformity improves, but the device complexity and manufacturing cost increase
Solution Approach 1:
Instead of physically modifying the power line structure (such as using thicker or lower-resistance materials that would increase device complexity), the invention substitutes a signal processing approach. The display driver electronically calculates and applies correction factors to compensate for the IR drops, replacing the need for complex physical modifications to the power distribution network.
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 effectively reduces luminance variations and power consumption, enabling the production of larger and brighter displays with improved image quality by minimizing artifacts caused by IR drops, while allowing for predictable and uniform luminance across the display.
Implementation Method 1
voltage drops along power lines due to finite resistance
Implementation Method 2
an array of light emitting elements for emitting light
Data Source
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AI summary
An electroluminescent display system, comprising: a display composed of an array of regions, current to each of the regions provided by a pair of power lines, each region including an array of light emitting elements; a pixel driving circuit for independently controlling current to each light-emitting element in response to an image signal, wherein the intensity of light output by the light emitting elements is dependent upon the current provided to each light emitting element; and a display driver for receiving an input image signal and generating a converted image signal for driving the light emitting elements wherein the driver analyzes the input signal to estimate the current that would result along at least one of the power lines providing current to each of the regions, if employed without further modification, and generates the converted signal as a function of the image signal and the estimated currents.