Pixel Drive Circuit for Organic EL Display Degradation
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Solution Overview
Problem
Organic EL displays face issues with degradation and burn-in due to differences in light emission intensity and frequency across pixels, leading to reduced contrast and image quality.
Innovation Solution
A pixel circuit comprising an organic EL element, a storage capacitor, and two p-channel transistors that supply drive and charge currents, with the second transistor providing a charge current to the capacitor, allowing the organic EL element to emit light for a longer period as it degrades, thereby compensating for current decreases and maintaining light emission intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the organic EL element emits light frequently with high intensity, then the light emission intensity is improved, but the degradation and burn-in of the pixel occurs
Solution Approach 1:
The pixel circuit dynamically adjusts the drive current supplied to the organic EL element based on real-time voltage monitoring. The second driving transistor continuously charges the storage capacitor, and the first driving transistor adjusts the drive current according to the voltage drop across the EL element, enabling adaptive current control that prevents excessive stress on degraded pixels while maintaining brightness for healthy ones
Solution Approach 2:
The circuit implements feedback control by monitoring the voltage drop across the organic EL element and using this information to regulate the drive current. The second driving transistor senses the voltage at the gate and adjusts the charge current to the storage capacitor accordingly, creating a closed-loop system that automatically compensates for pixel degradation without external intervention
2Illumination intensity
If the drive current is increased to maintain light emission intensity, then the illumination is improved, but the burn-in occurs more frequently
Solution Approach 1:
The circuit changes the drive parameter (current) dynamically based on the actual state of the organic EL element. By monitoring the voltage drop across the EL element and adjusting the drive current accordingly, the system ensures that pixels receive only the necessary current to maintain acceptable brightness, avoiding the harmful effect of excessive current that causes burn-in
Solution Approach 2:
The storage capacitor pre-stores charge that can be discharged to compensate for voltage drops during operation. This beforehand accumulation of energy provides a buffer that allows the circuit to maintain stable drive current even as the EL element degrades, preventing sudden current spikes that could accelerate burn-in
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 solution automatically adjusts the light emission period based on the organic EL element's degradation, maintaining image quality and reducing burn-in by extending the emission time and correcting intensity drops.
Implementation Method 1
an organic EL element which emits light in accordance with a drive current
Implementation Method 2
a storage capacitor which is charged with a data voltage
Data Source
AI summary
A pixel circuit includes an organic EL element includes a storage capacitor charged with a data voltage; a first driving transistor responsive to charged voltage of the storage capacitor to supply drive current to the organic EL element; and a second driving transistor connected the storage capacitor and a predetermined power supply responsive to potential corresponding to a voltage drop in the organic EL element, and supplies charge current to the storage capacitor, circuitry for causing the second driving transistor to supply charge current to the storage capacitor from a time when the storage capacitor is charged with data voltage and the drive current from first driving transistor flows through the organic EL element. When drive current from the first driving transistor is stopped by changes in the charged voltage of storage capacitor, the drive current supplied to the organic EL element for a period corresponding to the data voltage.