OLED Pixel Circuit Bootstrap Voltage Compensation
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Solution Overview
Problem
In organic light-emitting diode (OLED) display apparatuses, the non-uniformity of luminance occurs due to variations in the voltage across different light-emitting elements, affecting the driving current and causing display inconsistencies.
Innovation Solution
A pixel circuit comprising a driving transistor, storage capacitor, data writing module, and predetermined voltage writing module, where the storage capacitor is configured to maintain a predetermined potential and store data voltage independently of the light-emitting element's voltage, ensuring the driving current is unaffected by the voltage across the light-emitting element through a bootstrap effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the storage capacitor is directly connected to the light-emitting element terminal, then the circuit structure is simple, but the driving current is affected by voltage variations causing luminance non-uniformity
Solution Approach 1:
The pixel circuit is divided into distinct functional modules: a first writing module for storing reference voltage, a second writing module for storing data voltage, and a driving module. This segmentation allows independent control of voltage storage functions, preventing voltage variations from affecting driving current while maintaining clear functional separation.
Solution Approach 2:
The storage capacitor is introduced as an intermediary element between the light-emitting element and the voltage sources. It stores reference voltage and data voltage independently, mediating the voltage signals to ensure stable driving current without direct connection to the light-emitting element terminal, thus eliminating luminance non-uniformity.
2Duration of action of moving object
If the storage capacitor stores voltage during light emission, then the driving current is maintained, but voltage variations across light-emitting elements cause non-uniform luminance
Solution Approach 1:
The storage capacitor performs preliminary voltage storage before the light-emitting element emits light. The reference voltage is stored in advance during a pre-charge phase, and data voltage is stored during a compensation phase before light emission. This preliminary action ensures the driving current is predetermined and unaffected by voltage variations during light emission, maintaining both current stability and luminance uniformity.
Solution Approach 2:
The circuit incorporates a compensation mechanism where the storage capacitor stores data voltage that compensates for threshold voltage variations of the driving transistor. This feedback-like compensation ensures that despite process variations, the driving current remains uniform across different pixels, resolving the luminance non-uniformity issue while maintaining continuous driving current.
3Use of energy by moving object
If a conventional pixel circuit is used, then the power consumption is low, but process variations cause voltage differences leading to luminance non-uniformity
Solution Approach 1:
The invention changes the voltage storage parameters by introducing separate reference voltage storage and data voltage storage functions. The storage capacitor stores reference voltage at a predetermined level independent of light-emitting element voltage, and separately stores data voltage. This parameter separation ensures that process variations do not cause voltage differences affecting luminance uniformity, while the overall low-power operation is maintained through efficient voltage management.
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 eliminates the influence of the light-emitting element's voltage on the driving current, thereby enhancing the uniformity of luminance and stability of the OLED display, reducing issues related to aging and threshold voltage drift.
Implementation Method 1
ensuring the driving current is unaffected by the voltage across the light-emitting element through a bootstrap effect
Data Source
AI summary
There are disclosed a pixel circuit and a driving method of the same and a display apparatus. The pixel circuit comprises: a driving transistor (Tr), a storage capacitor (Cs), a data writing module (10), a light-emitting element (20) and a predetermined voltage writing module (30). A first terminal of the storage capacitor (Cs) is connected to a gate of the driving transistor (Tr) and a second terminal thereof is connected to a second electrode of the driving transistor (Tr). The predetermined voltage writing module (30) is configured to make the second electrode of the driving transistor (Tr) reach a predetermined potential in a pre-charging phase and a compensating phase; and the data writing module (10) is configured to store a data voltage of a data line into the storage capacitor (Cs) in the compensating phase. In the pixel circuit and the driving method thereof and the display apparatus, the driving current is not affected by the threshold voltage, and influence of the voltage across the light-emitting element on the driving current is eliminated, thereby the uniformity of luminance of the light-emitting element is raised and improving the display effect of the display apparatus is improved.