Organic EL Display Pixel Circuit for Luminance Uniformity
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Solution Overview
Problem
Conventional organic EL displays face challenges in accurately detecting variations in characteristics of driving transistors, leading to uneven luminance among pixels, due to the difficulty in measuring fine currents and the influence of noise from common power supplies and electrodes.
Innovation Solution
A display device with a luminescence element, a capacitor, and a driving transistor, along with a data line and switching elements, allows for accurate detection of drain currents by using a signal voltage to measure electric potential at the connection point between the luminescence element and the driving transistor, enabling correction of uneven luminance through calculation of gain coefficients and threshold voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current measurement methods are used to detect transistor characteristics, then measurement can be performed, but measurement precision deteriorates due to difficulty in measuring fine currents and noise from common power supplies
Solution Approach 1:
The patent segments the measurement process by using separate test power supply lines for each pixel during measurement, isolating the measurement path from the common power supply noise. Each pixel has its own dedicated test power line connected to the test transistor, allowing independent current measurement without interference from other pixels' power supplies.
Solution Approach 2:
The patent introduces a test transistor as an intermediary component between the data line and the organic EL element. This test transistor serves as a mediator that allows voltage measurement at the organic EL element's electrode without requiring direct current measurement through the common power supply, thereby eliminating noise interference.
2Measurement precision
If complicated pixel circuitry is used for characteristic detection, then measurement precision improves, but device complexity increases
Solution Approach 1:
The test transistor serves multiple functions: it acts as a switching element during normal display operation and as a measurement component during characterization testing. The same data line is used for both driving the organic EL element and measuring voltage at its electrode, eliminating the need for separate measurement circuitry.
Solution Approach 2:
The existing data line and organic EL element electrode structure is utilized for measurement purposes without adding separate measurement infrastructure. The system uses its own operational components (data line, electrode) to perform the measurement function, making the measurement capability self-contained within the existing architecture.
3Stability of the object's composition
If feedback compensation using representative pixel or sum of currents is used, then luminance uniformity improves, but device complexity and loss of information increase
Solution Approach 1:
The patent measures voltage at the specific electrode of each individual organic EL element, obtaining pixel-specific characteristic information. This local measurement approach captures the unique electrical characteristics of each pixel's transistor and organic EL element combination, enabling individualized compensation rather than global average compensation.
Solution Approach 2:
The measured voltage information at each pixel's electrode is fed back to the control circuitry, which then uses this information to adjust drive signals. This feedback mechanism allows real-time compensation for transistor and organic EL element variations, correcting luminance non-uniformity based on actual measured characteristics of each pixel.
Data Source
AI summary
A display device includes an organic EL element and a capacitor. A driving transistor is connected to an anode of the organic EL element and passes a current to the organic EL element. The current corresponds to a voltage held in the capacitor. A first switch is between the capacitor and a data line, and the data line supplies the voltage to the capacitor. A voltage detector is connected to the data line for detecting an anode voltage applied to the organic EL element. A second switch is between the anode and the data line. A controller turns on the first switch, causes the organic EL element to emit light, and causes the voltage detector to detect the anode voltage by turning off the first switch and turning on the second switch while the organic EL element is emitting light.