Pixel Circuit Segmentation for OLED Threshold Voltage Compensation
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Solution Overview
Problem
Large-sized organic light emitting displays face issues with non-uniform image quality due to threshold voltage deviations in driving transistors, leading to increased initialization time and potential unwanted light emission during initialization, which degrades contrast ratio and picture quality.
Innovation Solution
A pixel circuit design that separates initialization and threshold voltage compensation, using a specific configuration of N-type Metal Oxide Semiconductor (NMOS) transistors and capacitors to manage scanning signals and power voltages, allowing for sequential and delayed scanning signals to optimize data writing, initialization, and light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If initialization is performed simultaneously with threshold voltage compensation, then initialization time is reduced, but unwanted light emission occurs during initialization degrading contrast ratio and picture quality
Solution Approach 1:
The pixel circuit separates initialization and threshold voltage compensation into distinct time periods by using multiple scanning lines. The initialization operation is performed during a first time period when the initialization scanning line is active, while threshold voltage compensation occurs during a second time period when the compensation scanning line is active. This temporal segmentation prevents simultaneous operation and eliminates unwanted light emission during initialization.
2Reliability
If multiple scanning lines are used to separate initialization and compensation operations, then picture quality is improved, but device complexity increases
Solution Approach 1:
The circuit divides the scanning function into multiple dedicated scanning lines: a first scanning line for data writing, a second scanning line for initialization, and a third scanning line for threshold voltage compensation. Each scanning line controls specific transistors to perform its designated function independently, achieving picture quality improvement through functional segmentation while maintaining manageable circuit complexity.
Solution Approach 2:
The pixel circuit integrates multiple functions within a unified structure that shares common elements. The emission transistor serves both data writing and light emission functions, while capacitors are used for both data storage and threshold voltage compensation. This multi-functionality reduces overall device complexity despite the presence of multiple scanning lines.
3Object-affected harmful factors
If initialization and threshold voltage compensation are separated into different time periods, then unwanted light emission is reduced, but initialization time increases
Solution Approach 1:
The initialization operation is performed as a preliminary action before the threshold voltage compensation and light emission phases. By activating the initialization scanning line in the first time period to complete initialization beforehand, the circuit ensures that the organic light emitting diode is properly prepared without subsequent unwanted light emission during the compensation phase, optimizing both picture quality and time management.
Data Source
AI summary
A pixel circuit including an organic light emitting diode. Also, the pixel circuit includes: a second transistor connected to a first scanning line, a data line, and a first node; a fifth transistor connected to a third scanning line, the first node, and a second node; a fourth transistor connected to a second scanning line, a first reference voltage, and the second node; a third transistor connected to the first scanning line, a second reference voltage, and a third node; a first capacitor connected between the first node and the second node; a second capacitor connected between the second node and the third node; and a first transistor connected to the first node, a first power, and the third node, and configured to drive the organic light emitting diode.