Light-Emitting Device Driver Circuit Threshold Voltage Correction
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Solution Overview
Problem
In active matrix display devices with light-emitting elements, variations in threshold voltages of driving transistors lead to uneven luminance, and the high current requirements for driver circuits result in a significant load, especially when n-channel transistors are used, causing decreased luminance due to electroluminescent material deterioration.
Innovation Solution
A method involving a capacitor to hold the voltage between the gate and source of a transistor, allowing for controlled potential corrections and reduced load on the driver circuit by supplying specific potentials to the gate and source of the transistor, with a capacitance value smaller than the light-emitting element, to manage threshold voltage and anode potential corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a power supply scanner is used to control the potential of the power supply line, then threshold voltage correction can be performed, but the driver circuit requires high current supply performance and has a large load
Solution Approach 1:
The patent divides the correction process into separate phases: first applying a correction potential to the gate electrode to correct threshold voltage, then separately correcting the anode potential. This segmentation allows the driver circuit to handle correction signals independently from the main current supply, reducing the instantaneous current load on the driver circuit while maintaining correction effectiveness.
Solution Approach 2:
The patent applies threshold voltage correction to the gate electrode before the main light-emitting operation. By pre-correcting the threshold voltage in advance, the system ensures that the driving transistor operates with accurate threshold values during normal operation, eliminating the need for the driver circuit to continuously supply large correction currents during the main operation phase.
2Device complexity
If a switching transistor with n-channel is used to connect the drive transistor to the power supply line, then the structure is simplified, but the driver circuit requires sufficiently large voltage amplitude and has a large load
Solution Approach 1:
The patent applies different potential correction strategies to different parts of the circuit: the gate electrode receives threshold voltage correction, while the source electrode potential is adjusted separately. This localized correction approach allows the n-channel switching transistor to operate with standard voltage amplitudes while still achieving the desired correction效果, reducing the driver circuit's voltage supply requirements.
Solution Approach 2:
The patent introduces an intermediary correction mechanism where the gate electrode potential is adjusted to compensate for threshold voltage variations, and the source electrode potential is separately controlled. This intermediary correction approach allows the n-channel transistor to function with simpler structure while the driver circuit only needs to supply small correction currents through the intermediary correction paths.
3Duration of action of stationary object
If the voltage between anode and cathode is increased due to electroluminescent material deterioration, then the light-emitting element can maintain operation, but the gate voltage decreases and drain current decreases resulting in decreased luminance
Solution Approach 1:
The patent implements feedback correction by monitoring the actual operating conditions of the light-emitting element and adjusting the gate and source potentials accordingly. When anode potential increases due to material deterioration, the feedback mechanism detects this change and automatically adjusts the gate voltage and source voltage to maintain stable drain current and luminance output throughout the element's operational lifetime.
Solution Approach 2:
The patent dynamically changes the operating parameters (gate voltage and source voltage) to compensate for the increasing anode-cathode voltage. By adjusting these parameters in response to material deterioration, the system maintains constant drain current and luminance output, counteracting the harmful effect of electroluminescent material aging.
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 method effectively reduces the load on the driver circuit, corrects threshold voltage and anode potential, and maintains consistent luminance by supplying a potential obtained by adding the image signal voltage and threshold voltage to the gate electrode, thereby improving the efficiency and stability of light-emitting device operation.
Implementation Method 1
a voltage between a gate electrode of the transistor and a source of the transistor is held in a capacitor
Data Source
AI summary
A method for driving a light-emitting device comprises steps of: supplying a first potential to a drain of a transistor and a second potential being lower than the first potential to a cathode of a light-emitting element; supplying a third potential which is lower than a potential obtained by adding the threshold voltage of the transistor, the threshold voltage of the light-emitting element, and the second potential to a gate electrode of the transistor, and a fourth potential being lower than a potential obtained by subtracting the threshold voltage of the transistor from the third potential to the source of the transistor; stopping supply of the fourth potential to the source of the transistor; and supplying a potential of an image signal to the gate electrode of the transistor.