OLED Driving Circuit Threshold Voltage Correction
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Solution Overview
Problem
Conventional methods for driving organic electroluminescence (EL) display devices do not effectively address the visible 1-frame luminance fluctuation caused by drive transistor threshold voltage fluctuations, leading to unstable light emission.
Innovation Solution
A driving method that includes a resetting step to apply a reset voltage to the drive transistor, suppressing threshold voltage fluctuations, and adjusting voltages to ensure precise light emission by the organic EL element, using a power source circuit with a light-emitting element, drive transistor, capacitive element, and switching transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional pixel circuit configuration is used, then device complexity is reduced, but luminance stability deteriorates due to threshold voltage fluctuations
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage identification and storage before the actual light emission process. The control circuit measures the threshold voltage of the drive transistor and stores it in memory, then uses this stored value to correct the gray scale voltage before applying it to the organic EL element. This preliminary characterization and correction prevents threshold voltage fluctuations from causing luminance instability during normal operation.
Solution Approach 2:
The patent implements feedback through the threshold voltage identification process where the control circuit continuously monitors and measures the actual threshold voltage of the drive transistor. This measured feedback value is then used to correct the driving voltage applied to the organic EL element, creating a closed-loop system that compensates for threshold voltage variations and maintains stable luminance output.
2Reliability
If threshold voltage correction is applied, then luminance stability is improved, but 1-frame luminance fluctuation remains visible
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the gray scale voltage based on the identified threshold voltage. The control circuit calculates a corrected gray scale voltage by adding a compensation value derived from the threshold voltage measurement. This parameter adjustment ensures that the voltage applied to the organic EL element compensates for transistor threshold variations, reducing but not completely eliminating 1-frame luminance fluctuations.
3Reliability
If more circuit components are added to reduce threshold voltage fluctuation, then luminance stability is improved, but device complexity increases
Solution Approach 1:
The patent applies universality by making the control circuit perform multiple functions: it identifies threshold voltage, stores the threshold value in memory, corrects gray scale voltage based on the measured threshold, and controls the display output. This multi-functional approach reduces the need for separate dedicated circuit components for each function, thereby maintaining luminance stability while minimizing the increase in device complexity.
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 reduces errors in current supply to the light-emitting element, resulting in more precise and stable luminance, improving display quality by minimizing luminance fluctuations and eliminating trailing issues during scrolling displays.
Implementation Method 1
a capacitive element connected to a gate electrode of the driving transistor, for holding a data voltage
Implementation Method 2
the display device uses organic electroluminescence (EL) elements
Data Source
AI summary
A method of driving a display device including pixels in a matrix and a power source, each pixel including a light-emitting element, drive transistor, capacitance element, and switching transistor, and connected to the power source by a power line, the method including: setting a voltage across the light-emitting element smaller than or equal to its threshold voltage by adjusting a voltage outputted by the power source to the power line; (a) applying, to a gate of the drive transistor, a reset voltage with which the gate-source voltage of the drive transistor becomes larger than its threshold voltage; (c) causing a data voltage to be held in the capacitive element; and (d) causing the light-emitting element to emit light according to the data voltage by setting the voltage across the light-emitting element larger than its threshold voltage by adjusting the voltage outputted by the power source to the power line.