EL Display Current Detection Using Shared Successive Approximation ADC
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Solution Overview
Problem
Current active matrix electroluminescence (EL) display apparatuses face issues with brightness unevenness due to variations in the threshold value of thin-film transistors (TFTs), leading to reduced yield and difficulty in correcting display defects after shipment, especially with increased pixel resolution and the need for complex measurement and correction processes.
Innovation Solution
An EL display apparatus with a driving section that includes a variation detecting system to measure current variations through electroluminescence elements during blanking periods, using a successive approximation type analog-digital converter to convert current signals into digital form for rapid correction, allowing for real-time detection and correction of display variations without requiring increased camera resolution or storage capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a camera-based measurement system is used to detect brightness variation in each pixel, then display variation can be measured, but the system complexity and cost increase significantly with higher pixel resolution
Solution Approach 1:
The patent replaces the optical measurement system (camera-based brightness detection) with an electrical measurement system. Instead of using a camera to capture and analyze light emission from each pixel, the invention uses a current detection amplifier to directly measure the cathode current flowing through each EL element. This substitution of measurement method eliminates the need for complex optical systems while maintaining measurement precision.
Solution Approach 2:
The patent introduces a current detection amplifier as an intermediary device between the EL element and the measurement system. This amplifier detects the cathode current that flows through each pixel's EL element and converts it into a measurable signal. By measuring the current that directly drives the light emission, the system achieves accurate brightness variation detection without requiring complex optical measurement equipment.
2Manufacturing precision
If the number of pixels in the EL panel is increased to improve resolution, then display quality improves, but the number of measurement and correction targets increases
Solution Approach 1:
The patent replaces the camera-based optical measurement approach with direct electrical current measurement. By measuring the cathode current of each EL element through a current detection amplifier, the system can handle high-resolution panels without proportionally increasing measurement system complexity. The electrical measurement method is more scalable and efficient than optical methods for high-density pixel arrays.
3Manufacturing precision
If correction information is stored for each pixel to enable display variation correction, then display uniformity improves, but storage capacity requirements increase
Solution Approach 1:
The patent extracts only the essential correction information needed for display uniformity. Instead of storing complete correction datasets for all pixels, the system measures cathode current variations and stores only the necessary correction values. This selective extraction of correction data reduces storage requirements while maintaining display uniformity.
4Reliability
If a circuit for correcting Vth variation is incorporated in each pixel, then display variation correction capability improves, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent replaces complex in-pixel correction circuits with a centralized current measurement and correction system. Instead of incorporating Vth correction circuits within each pixel, the invention measures the actual cathode current of each EL element using a current detection amplifier and applies correction based on these measurements. This approach achieves reliable display variation correction while avoiding the complexity of in-pixel correction 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
Enables speedy measurement and correction of display variations post-shipment, reducing the complexity of measurement structures and increasing processing efficiency, while downsizing the apparatus by sharing digital-analog converters and reducing the number of amplifiers and converters needed.
Implementation Method 1
an electroluminescence element which emits light in accordance with a current that flows therethrough
Implementation Method 2
a current detection amplifier that detects a current that flows through the electroluminescence element
Data Source
AI summary
During a blanking period of a video signal, an element driving transistor for controlling a drive current supplied to an EL element is operated in its saturation region to thereby set the EL element to an emission level, and a current flowing through the EL element at that time is detected. Each current detector includes a current detection amplifier and a successive approximation type AD converter, and a DA converter of the successive approximation type AD converter is commonly shared among a plurality of the AD converters. With this arrangement, sufficient AD converting speed can be attained while using a simple structure to execute current detection for correcting display variations.