Organic EL Pixel Circuit Mobility Correction via Precharge
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Solution Overview
Problem
In organic EL display apparatuses, the variation in mobility correction time leads to variations in brightness, degrading image quality due to the short optimal mobility correction time and discontinuous determination of write pulse width, which is challenging to optimize effectively.
Innovation Solution
The display apparatus includes a pixel array section with write and drive transistors, and a write scan circuit that supplies a write pulse to extend the mobility correction time by precharging the gate-to-source voltage of the drive transistor, allowing for a longer optimal mobility correction time and reducing variations in brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the mobility correction time is extended to reduce brightness variations, then the optimal write pulse width can be determined more accurately, but the pixel circuit complexity increases due to additional transistors and capacitors required for mobility correction
Solution Approach 1:
The patent combines the mobility correction function with the existing pixel circuit components by having the drive transistor perform dual functions: driving the light-emitting element and enabling mobility correction through timing control. The write transistor and holding capacitor are utilized for both signal writing and mobility correction, merging multiple functions into fewer components.
Solution Approach 2:
The patent introduces dynamic timing control where the write pulse width is adjusted based on the mobility correction time. The mobility correction period is dynamically determined by the write pulse duration, allowing the circuit to adapt the correction time to match the specific mobility characteristics of each pixel without requiring additional fixed-time correction circuits.
2Manufacturing precision
If additional compensation functions are added to correct threshold voltage and mobility variations, then the emission brightness uniformity improves, but the pixel circuit structure becomes more complex with more transistors and capacitors
Solution Approach 1:
The drive transistor serves multiple functions: it acts as the switching element for the light-emitting element, the mobility correction element, and the threshold voltage compensation element. The holding capacitor similarly serves dual purposes in signal holding and mobility correction, reducing the need for separate dedicated components for each compensation function.
Solution Approach 2:
The pixel circuit uses its own internal components (drive transistor, write transistor, holding capacitor) to perform mobility correction and threshold compensation without requiring external assistance or additional dedicated correction circuits. The circuit self-corrects for manufacturing variations using its existing structure and timing control mechanisms.
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 approach ensures a relatively smaller variation in mobility correction time, suppressing brightness variations and enabling optimal write pulse width settings, thereby improving image quality by maintaining consistent emission brightness across pixels.
Implementation Method 1
The organic EL element relies on the phenomenon that the organic thin film thereof emits light when an electric field is applied thereto
Implementation Method 2
the current flowing through the light-emitting element is controlled by an active element provided together with the light-emitting element in the same pixel circuit such as insulated gate electric field effect transistor (generally TFT (Thin Film Transistor))
Data Source
AI summary
Prior to increasing the voltage level of an input signal to be sampled in a step-by-step manner and writing a signal voltage Vsig at a desired voltage level, a precharge is performed which writes a precharge voltage Vpre, lower than the signal voltage Vsig, so as to apply the same voltage Vpre to the gate of a drive transistor in advance. This not only provides a reduced gate-to-source voltage of the drive transistor at the time of writing of the signal voltage Vsig but also extends a mobility correction time required for a mobility correction operation. The extension of the mobility correction time required for the mobility correction operation ensures a relatively smaller variation in the correction time, thus suppressing the variation in brightness. The extension also permits a write pulse to be set to the optimal pulse width.