OLED Pixel Circuit Boost Capacitor Black Brightness
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-definition and large-sized OLED display devices face issues with non-uniform brightness due to varying threshold voltages of driving transistors, leading to reduced contrast ratios and lifetime, especially when using time division driving methods that cause charge sharing and increased black brightness.
Innovation Solution
The implementation of a pixel circuit with a driving transistor, multiple switching transistors, a storage capacitor, and a boost capacitor, which allows for differential voltage charging and voltage boosting to maintain consistent driving voltage, preventing black brightness increase and improving contrast ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If time division driving is applied for high definition and large sized OLED display devices, then productivity is improved, but the data line becomes floated causing charge sharing that increases black brightness and drops contrast ratio
Solution Approach 1:
The patent introduces a fifth switching transistor as an intermediary element to prevent charge sharing between the storage capacitor and parasitic capacitor during time division driving. This switching transistor acts as a mediator that controls the connection between the data line and storage capacitor, allowing time division driving to maintain high productivity while preventing the harmful charge sharing effect that causes black brightness increase.
2Reliability
If threshold voltage sampling is performed during time division driving, then driving transistor characteristics are compensated, but the sampling period becomes inadequate causing driving voltage to rise and drop contrast ratio
Solution Approach 1:
The patent implements preliminary action by performing threshold voltage sampling before the main data writing operation in the time division driving sequence. The fifth switching transistor enables this preliminary sampling phase, allowing the driving transistor characteristics to be compensated in advance, thus ensuring adequate sampling time while maintaining overall driving efficiency and contrast ratio.
3Adaptability or versatility
If the data line is floated during threshold voltage sampling, then time division driving is enabled, but charge sharing occurs between parasitic capacitor and storage capacitor increasing driving voltage
Solution Approach 1:
The fifth switching transistor serves as a controlled intermediary that manages the data line connection during threshold voltage sampling. It enables the data line to be properly connected or disconnected based on the operation phase, preventing uncontrolled charge sharing while maintaining the time division driving capability. This intermediary element simplifies voltage control by providing a明确的 connection control mechanism.
Data Source
AI summary
An OLED display device for improving a contrast ratio is disclosed. The OLED display device includes a pixel circuit, wherein the pixel circuit includes a driving transistor driving the light emitting device, a first switching transistor supplying a data voltage from a data line to a first node in response to a first scan signal from a first scan line, a second switching transistor connecting the driving transistor to a power line in a diode structure in response to the first scan signal from the first scan line, a third switching transistor supplying a reference voltage from a reference voltage supply line to the first node in response to a light emission control signal from a light emission control line, a fourth switching transistor connecting the driving transistor to the light emitting device in response to the light emission control signal from the light emission control line, a fifth switching transistor connecting the fourth switching transistor to the reference voltage supply line in response to a second scan signal from the second scan line, a storage capacitor connected between the first node and a second node connected to a gate electrode of the driving transistor, and a boost capacitor connected to the first scan line and the second node.