OLED Pixel Circuit Luminance Uniformity via Threshold Correction
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Solution Overview
Problem
Existing pixel circuits for organic electroluminescence (OLED) displays face challenges in maintaining uniform light emission luminance due to variations in threshold voltage and mobility of drive transistors and organic EL elements, leading to luminance unevenness across the display.
Innovation Solution
A simplified pixel circuit configuration using a drive transistor, a holding capacitor, and a sampling transistor, along with a controller for threshold correction and mobility correction, which includes an initialization transistor to minimize additional components and interconnects, ensuring constant light emission by adjusting the drive current and compensating for variations in element characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel circuit with multiple transistors and capacitors is used to compensate for threshold voltage and mobility variations, then luminance uniformity is improved, but device complexity increases
Solution Approach 1:
The invention extracts and eliminates unnecessary components from the conventional pixel circuit. By removing redundant transistors and capacitors while retaining only the essential drive transistor, sampling transistor, and holding capacitor, the circuit achieves luminance uniformity without the complexity of full compensation circuits.
Solution Approach 2:
The pixel circuit uses its own inherent characteristics and timing sequences to achieve threshold voltage and mobility correction. The sampling transistor and holding capacitor work together with the drive transistor to automatically compensate for variations through the pixel circuit's natural operation cycles, without requiring external compensation circuits.
2Reliability
If additional transistors and capacitors are added for threshold and mobility correction, then luminance uniformity is improved, but the number of components increases
Solution Approach 1:
The sampling transistor serves multiple functions: it acts as a switching element for signal input and simultaneously provides threshold voltage and mobility correction. The holding capacitor not only stores the video signal but also participates in the correction process. This multi-functionality eliminates the need for separate correction components.
Solution Approach 2:
The invention merges the signal sampling function and the correction function into a unified circuit structure. The sampling transistor and holding capacitor are integrated to perform both signal storage and parameter correction, reducing the total component count while maintaining correction effectiveness.
3Reliability
If more interconnects are added for correction signals, then luminance uniformity is improved, but device complexity and area increase
Solution Approach 1:
The invention removes unnecessary interconnect lines that would be required for separate correction circuits. By eliminating redundant transistors and capacitors, the corresponding interconnects are also removed, simplifying the overall wiring structure while maintaining correction functionality through the integrated sampling and holding mechanism.
4Device complexity
If a simplified pixel circuit with fewer components is used, then device complexity is reduced, but luminance uniformity deteriorates due to threshold voltage and mobility variations
Solution Approach 1:
The pixel circuit implements an inherent feedback mechanism where the holding capacitor stores the relationship between the drive transistor parameters and the required correction. Through the timing sequence and circuit operation, the system automatically adjusts for threshold voltage and mobility variations, maintaining luminance uniformity without complex external feedback circuits.
Data Source
AI summary
There is provided a display including: a pixel array part configured to include pixel circuits arranged in a matrix, each of the pixel circuits having a drive transistor, a holding capacitor, an electro-optical element, a sampling transistor, and an initialization transistor, a drive current based on information held in the holding capacitor being produced by the drive transistor and being applied to the electro-optical element for light emission of the electro-optical element; and a controller configured to include a write scanner, a horizontal driver, and an initialization scanner.