Pixel Circuit for High-Speed Writing and Threshold Compensation
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Solution Overview
Problem
The existing active-matrix organic EL display apparatus faces challenges in achieving high-speed writing operations and compensating for threshold voltage fluctuations, which limits the development of large-sized or high-definition displays due to the slow discharging speed of capacitors and the shared use of data lines for image signal and threshold voltage compensation.
Innovation Solution
The proposed display apparatus incorporates a pixel circuit structure with multiple switches and capacitors, allowing for independent control of image signal voltage, reference voltage, initialization voltage, and light emission current, enabling high-speed writing operations and effective threshold voltage compensation without relying on data lines for compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a data line is used for both image signal supply and threshold voltage compensation, then device complexity is reduced, but writing speed becomes too slow for large-sized or high-definition displays
Solution Approach 1:
The patent divides the single data line function into separate pathways: one dedicated to image signal supply and another to threshold voltage compensation. This is achieved by introducing a separate compensation line that connects to the capacitor, allowing independent operation of writing and compensation processes without time multiplexing conflicts.
Solution Approach 2:
The patent introduces an intermediate capacitor structure with multiple connection points. The capacitor serves as an intermediary element that can receive signals from both the data line (for image signals) and the compensation line (for threshold voltage compensation), enabling simultaneous or independent operation of both functions without direct conflict.
2Measurement precision
If the capacitor terminal voltage is reduced toward the threshold voltage to improve display accuracy, then image quality improves, but discharging time becomes excessively long
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor to a voltage higher than the threshold voltage through the compensation line before the actual writing operation. This preliminary charging ensures that when the image signal is written, the capacitor can quickly discharge to the precise threshold voltage level without requiring excessive discharge time, as the voltage differential is optimized from the start.
Solution Approach 2:
The patent changes the voltage parameter of the capacitor dynamically through separate control pathways. The compensation line independently adjusts the capacitor voltage to optimal levels, allowing the system to maintain high discharge speeds while achieving precise threshold voltage compensation. The voltage parameters are optimized separately for speed (higher initial voltage) and accuracy (precise final voltage level).
Data Source
AI summary
A pixel circuit has a first capacitor having a first terminal connected with a gate of a driving transistor; a second capacitor connected between a second terminal of the first capacitor and a source of the driving transistor; a first switch applying a reference voltage to a node at which the first capacitor and the second capacitor are connected; a second switch supplying an image signal voltage to the gate of the driving transistor; a third switch supplying an initialization voltage to a drain of the driving transistor and a fourth switch supplying current to the drain of the transistor for emitting light from the current light emitting device.