OLED Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
Organic light emitting displays (OLEDs) face efficiency decreases and image sticking due to prolonged carrier movement, leading to shortened lifespan and image retention issues.
Innovation Solution
The implementation of a specific organic light emitting display configuration, including switching elements, storage capacitors, and a driving transistor, which controls current supply to the OLED and compensates for threshold voltage irregularities, ensuring consistent light emission and reducing image sticking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If continuous current is supplied to OLED to maintain light emission, then display operation is maintained, but carrier accumulation occurs leading to efficiency decrease and image sticking
Solution Approach 1:
The patent applies periodic action by controlling the current supply to OLED in discrete time intervals rather than continuously. The current is supplied only during the light emission period controlled by the light emission control signal, and stopped during other periods. This periodic current supply prevents carrier accumulation at electrodes while maintaining display operation, thereby resolving the contradiction between maintaining display operation and preventing image sticking.
2Illumination intensity
If high current is supplied to OLED to maintain brightness, then light emission intensity is improved, but efficiency decreases due to carrier accumulation
Solution Approach 1:
The patent uses periodic action by controlling current supply duration through the light emission control signal. Current is supplied only when light emission is required, preventing carrier accumulation that would reduce efficiency. This maintains high light emission intensity during active periods without the negative effects of continuous high current supply.
3Device complexity
If simple current control circuit is used to reduce complexity, then device complexity is reduced, but threshold voltage compensation precision is insufficient
Solution Approach 1:
The patent applies self-service by using the pixel circuit's own components (storage capacitors, switching elements) to automatically compensate for threshold voltage variations. The circuit self-adjusts the driving current based on stored voltage values that account for transistor threshold voltage differences, eliminating the need for external complex compensation circuits while achieving precise compensation.
4Reliability
If multiple switching elements and capacitors are added to control current and compensate threshold voltage, then image sticking is suppressed and grayscale precision is improved, but device complexity increases
Solution Approach 1:
The patent applies multi-functionality by designing pixel circuit components to serve multiple purposes. The storage capacitors not only maintain voltage but also enable threshold voltage compensation. The switching elements not only control current timing but also facilitate the compensation mechanism. This integration allows image sticking suppression and grayscale precision improvement without proportionally increasing circuit 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 configuration enhances OLED efficiency, reduces image sticking, and enables high-grayscale displays by maintaining consistent current supply and compensating for threshold voltage variations, thereby extending the OLED lifespan.
Implementation Method 1
The organic light emitting display emits light by electrically exciting a fluorescent or phosphorescent compound. At the EML, the electron(s) supplied from the ETL and the hole(s) supplied from the HTL may recombine with each other, thereby generating a predetermined amount of light.
Implementation Method 2
a first storage capacitor that is electrically coupled between the first voltage line and the control electrode of the driving transistor
Implementation Method 3
a first switching element including a control electrode electrically coupled to a scan line and being electrically coupled between a data line and a first voltage line
Data Source
AI summary
An organic light emitting display includes a first switching element including a control electrode electrically coupled to a scan line and between a data line and a first voltage line, a driving transistor electrically coupled between the first voltage line and a second voltage line, a second switching element including a control electrode electrically coupled to a light emission control line and between the first voltage line and the driving transistor, a third switching element including a control electrode electrically coupled to the scan line and between the second switching element and the driving transistor, a first storage capacitor that is electrically coupled between the first voltage line and the control electrode of the driving transistor, a second storage capacitor that is electrically coupled between the first storage capacitor and the second switching element, and an OLED electrically coupled between the driving transistor and the second voltage line.