Organic EL Display Pixel Circuit Mobility Correction
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Solution Overview
Problem
In organic EL display apparatuses, the emitted light luminance varies due to characteristic variations of transistors, such as threshold voltage and mobility changes, leading to non-uniformity in screen images.
Innovation Solution
A display apparatus with a pixel array, writing and driving transistors, storage capacitors, and a detection section to control the mobility correction period based on detected transistor characteristic variations, ensuring consistent light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple matrix type driving method is used, then the structure is simple, but it is difficult to implement as a large-sized high definition display apparatus because the light emitting period decreases as the number of scanning lines increases
Solution Approach 1:
The pixel circuit is segmented into multiple functional components: a driving transistor for current control, a switching transistor for signal input, and a storage capacitor for maintaining the gate voltage. This segmentation allows the pixel to maintain its light-emitting state independently throughout the frame period, enabling large-sized high definition displays while keeping the overall structure relatively simple.
2Duration of action of moving object
If an active matrix type is used, then the electro-optical element continues to emit light over one frame period, but the transistor characteristic variations cause luminance non-uniformity across pixels
Solution Approach 1:
The pixel circuit incorporates a feedback mechanism where the storage capacitor maintains the gate voltage of the driving transistor throughout the frame period. This feedback loop compensates for transistor characteristic variations by keeping the driving voltage stable, thereby ensuring uniform luminance across all pixels even when transistor parameters vary due to manufacturing tolerances.
3Duration of action of stationary object
If the I-V characteristic of the organic EL element deteriorates with aging, then the gate-source voltage of the driving transistor varies, causing luminance variation
Solution Approach 1:
The storage capacitor is charged in advance during the scanning period to store the appropriate gate voltage. This preliminary action ensures that when the transistor characteristics change due to aging or temperature variations, the stored voltage compensates for these changes, maintaining stable luminance output throughout the operational lifetime of the display.
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
The solution maintains consistent emitted light luminance across pixels, enhancing display image quality by adjusting the mobility correction period in response to transistor characteristic changes.
Implementation Method 1
an organic EL (Electro Luminescence) element which utilizes a phenomenon that an organic thin film emits light when an electric field is applied thereto
Data Source
AI summary
Disclosed herein is a display apparatus, including: a pixel array section configured to have a plurality of pixels arranged in a matrix thereon, each of the pixels including an electro-optical element, a writing transistor, a driving transistor, and a storage capacitor connected between the gate electrode and the source electrode of the driving transistor for storing an image signal written by the writing transistor, each of the pixels carrying out a mobility correction process for applying negative feedback to a potential difference between the gate and the source of the driving transistor with a correction amount determined from current flowing to the driving transistor; a detection section configured to detect variation of a characteristic of any transistor in the pixels; and a control section configured to control the period of the mobility correction process based on a result of the detection by the detection section.