Organic EL Display Driving Circuit with Preliminary Potential Fixing
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Solution Overview
Problem
In organic EL display apparatuses, it is challenging to allocate sufficient time for reliable threshold-voltage correction and mobility correction operations due to increasing pixel counts and shorter horizontal scan periods, leading to variations in luminance across the screen.
Innovation Solution
A display apparatus with a pixel array section, write transistor, holding capacitor, and driving transistor, along with a driving circuit that performs a preparatory operation to fix gate and source potentials, allowing for a prolonged threshold-voltage correction period and ensuring reliable correction operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of pixels is increased to achieve high-resolution displays, then the display resolution is improved, but the horizontal scan period becomes shorter making it difficult to allocate sufficient time for correction operations
Solution Approach 1:
The patent applies preliminary action by performing the preparatory operation in the previous horizontal scan period before the actual threshold-voltage correction operation. Specifically, the electric potential at the source of the driving transistor is fixed at a predetermined level (Vccp) in advance, so that when the correction operation occurs in the current period, the transistor operates in a predictable region, enabling reliable correction within the shortened horizontal scan period of high-resolution displays
2Reliability
If sufficient time is allocated for reliable threshold-voltage correction and mobility correction operations, then the correction reliability is improved, but the horizontal scan period becomes longer reducing productivity
Solution Approach 1:
The patent performs the preparatory operation of fixing the source electric potential at a predetermined level (Vccp) in the previous horizontal scan period. This preliminary action ensures that during the threshold-voltage correction operation, the driving transistor operates in a predictable region, allowing the correction to be completed reliably within a shortened time frame, thus maintaining correction reliability while improving horizontal scan efficiency
Solution Approach 2:
The patent changes the electric potential parameter at the source of the driving transistor to a predetermined level (Vccp) during the preparatory operation. This parameter change ensures that the transistor operates in a predictable region (saturation region) during the correction operation, enabling reliable threshold-voltage correction to be performed within a shortened horizontal scan period, thereby resolving the contradiction between correction reliability and scan efficiency
3Device complexity
If the threshold-voltage correction operation is performed without fixing the source electric potential, then the device complexity is reduced, but the luminance uniformity deteriorates due to variations in correction accuracy
Solution Approach 1:
The patent changes the electric potential parameter at the source of the driving transistor to a predetermined level (Vccp) during the preparatory operation. This parameter change ensures that the transistor operates in a predictable region (saturation region) during the correction operation, enabling accurate threshold-voltage correction and ensuring uniform luminance across the display, while the complexity remains manageable through systematic control
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 enables reliable threshold-voltage and mobility corrections, maintaining uniform luminance and image quality even with high-resolution displays and reducing the need for additional time allocation during horizontal scan periods.
Implementation Method 1
An example of the electro-optical device of the so-called current-driven type is an organic EL device operating on the basis of a phenomenon in which a light beam is generated by the device when an electric field is applied to an organic film.
Implementation Method 2
An example of the active device is an insulated-gate type field effect transistor which is generally a TFT (thin film transistor).
Data Source
AI summary
A display apparatus and display driving method. A selective scan operation is performed on pixel circuits in row units, and a threshold-voltage correction operation is also performed to correct variations of the threshold voltage of respective pixel circuit driving transistors. Before performing the threshold-voltage correction operation in a horizontal scan period, a preparatory operation is performed in order to fix each of the electric potentials appearing on the gate and the source of the driving transistor at a predetermined level.