OLED Pixel Circuit Preventing Reset Light Emission
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Solution Overview
Problem
Conventional image display apparatuses using organic EL devices face issues with reduced contrast due to unnecessary light emission during the reset step, leading to unstable light emission conditions and impractical two-TFT configurations.
Innovation Solution
An image display apparatus with a configuration that includes a light emitting device, a drive transistor, a switching transistor, and a capacitor, where the drive transistor and capacitor are designed to prevent light emission during the reset step by controlling the potential difference across the light emitting device, ensuring it operates within specific threshold voltages to improve contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a two-TFT configuration is used to reduce device complexity, then the number of transistors per pixel is reduced, but light emission occurs during the reset step causing contrast degradation
Solution Approach 1:
The patent applies preliminary action by resetting the potential of the light emitting device before the actual reset operation. Specifically, a reset potential is applied in advance to ensure the potential difference remains below the light emission threshold during the reset step, preventing unwanted light emission while maintaining the simple two-TFT configuration
Solution Approach 2:
The patent changes the electrical parameters (potentials) applied to the light emitting device during different operation steps. By carefully controlling the reset potential and data potential values, the potential difference across the light emitting device is kept below the light emission threshold during reset, thereby preventing contrast degradation
2Ease of operation
If the potential difference during reset step is not controlled, then the reset operation is simple, but light emission occurs causing unstable light emission conditions
Solution Approach 1:
The patent implements parameter changes by applying specific reset potential and data potential values that control the potential difference across the light emitting device. This ensures the potential difference remains below the light emission threshold during reset, preventing unwanted light emission and stabilizing the light emission conditions
3Device complexity
If conventional reset operation is used, then the reset step is straightforward, but contrast is reduced due to unnecessary light emission
Solution Approach 1:
The patent changes the electrical parameters during reset by applying a reset potential that, when combined with the data potential, keeps the potential difference across the light emitting device below the light emission threshold. This prevents unwanted light emission during reset, improving contrast without significantly increasing operational complexity
Solution Approach 2:
The patent incorporates feedback by monitoring the potential difference across the light emitting device and adjusting the reset and data potentials accordingly. This ensures the potential difference remains within the safe range that prevents light emission, thereby maintaining high contrast ratio
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 effectively prevents light emission during the reset step, enhancing contrast and stability of the image display apparatus, allowing for practical implementation even with two-TFT configurations.
Implementation Method 1
organic EL (electroluminescence) devices, which have a function of generating light by emission due to recombination of holes and electrons injected in an emission layer
Data Source
AI summary
An image display apparatus includes a plurality of pixels. Each pixel includes a light emitting device; a drive transistor that has a gate electrode, a source electrode, and a drain electrode. One of the source and drain electrodes are electrically connected to one end of the light emitting device. Each pixel also includes a first switching transistor that electrically connects the gate electrode and the one electrode according to a scan signal, and a capacitor that has first and second electrodes. The first electrode is electrically connected to the gate electrode. The apparatus also includes a data line connected to the second electrode; a data line drive circuit that supplies a brightness potential and a reference potential for the brightness potential to the data line.