Pixel Driving Circuit for OLED Luminance Uniformity
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Solution Overview
Problem
Variation in threshold voltages of driving transistors in light-emitting devices leads to inconsistent luminance among pixels, and deterioration of the EL layer causes a decrease in luminance, affecting image quality.
Innovation Solution
A light-emitting device configuration with transistors, switches, and a capacitor that allows for independent control of gate and source/drain potentials, enabling compensation of threshold voltage variations and maintaining consistent current supply to the light-emitting elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an n-channel driving transistor is used with the light-emitting element configuration (anode-EL layer-cathode), then the device can be fabricated through a simple process, but the potential of the source increases when the voltage between anode and cathode increases, decreasing the gate voltage and reducing drain current
Solution Approach 1:
The patent inverts the conventional connection by using a p-channel transistor instead of an n-channel transistor. This inversion changes the polarity relationship between the transistor and light-emitting element, so that when the voltage between anode and cathode increases, the source potential decreases rather than increases, thereby maintaining or increasing the gate voltage and preventing drain current reduction
Solution Approach 2:
The patent changes the conductivity type parameter of the driving transistor from n-channel to p-channel. This parameter change fundamentally alters the electrical characteristics and voltage relationships in the circuit, resolving the issue where source potential increase leads to gate voltage decrease and drain current reduction
2Illumination intensity
If the voltage between anode and cathode is increased to compensate for EL layer deterioration, then the luminance can be maintained, but the source potential increases, decreasing the gate voltage and reducing the drain current
Solution Approach 1:
By inverting to a p-channel transistor, the patent reverses the voltage relationship so that increasing the voltage between anode and cathode causes the source potential to decrease, thereby increasing the gate voltage and maintaining drain current, allowing luminance compensation without operational degradation
Data Source
AI summary
A light-emitting device in which variation in luminance of pixels is suppressed. A light-emitting device includes at least a transistor, a first wiring, a second wiring, a first switch, a second switch, a third switch, a fourth switch, a capacitor, and a light-emitting element. The first wiring and a first electrode of the capacitor are electrically connected to each other through the first switch. A second electrode of the capacitor is connected to a first terminal of the transistor. The second wiring and a gate of the transistor are electrically connected to each other through the second switch. The first electrode of the capacitor and the gate of the transistor are electrically connected to each other through the third switch. The first terminal of the transistor and an anode of the light-emitting element are electrically connected to each other through the fourth switch.