AMOLED Pixel Circuit Hysteresis Compensation and Leakage Prevention
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Solution Overview
Problem
Existing pixel circuits for AMOLED displays face issues with image retention due to hysteresis characteristics of driving transistors and contrast deterioration from leaked light emission during non-emission periods, particularly when switching from black to white display and during capacitor reset periods.
Innovation Solution
A pixel circuit design that includes a driving transistor, a capacitor for holding threshold and data voltages, and a switch part that applies a constant voltage to the driving transistor before initializing the capacitor, ensuring secure current flow and preventing hysteresis initialization, while also using a current detour transistor to prevent leaked light emission during non-emission periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pixel circuit uses a driving transistor with hysteresis characteristic for threshold voltage detection, then the threshold voltage can be detected and compensated, but image retention occurs when switching from black to white display requiring several frames to transition
Solution Approach 1:
The invention applies a constant voltage to the driving transistor before initializing the capacitor to hold threshold and data voltages. This preliminary action ensures the transistor is in a known state with consistent current flow, preventing hysteresis initialization issues that cause image retention and enabling immediate display transition without requiring several frames.
2Reliability
If the pixel circuit flows electric current to the driving transistor during threshold voltage detection and capacitor reset periods, then the transistor remains active, but leaked light emission occurs in the OLED during non-emission periods causing contrast deterioration
Solution Approach 1:
The invention extracts the harmful function of current flow during non-emission periods by introducing a current detour transistor that redirects the current path. This allows the driving transistor to remain stable while preventing current from flowing through the OLED during capacitor reset periods, thereby eliminating leaked light emission and contrast deterioration.
Solution Approach 2:
The current detour transistor acts as an intermediary element that controls current flow paths. It enables the driving transistor to maintain stable operation while blocking current from reaching the OLED during non-emission periods, thus mediating between the need for transistor stability and the need to prevent leaked light emission.
Data Source
AI summary
To prevent image retention, the pixel circuit includes: a light emitting element; a driving transistor which supplies an electric current according to an applied voltage to the light emitting element; a capacitor part which holds the voltage containing a threshold voltage and a data voltage of the driving transistor; and a switch part which has the voltage containing the threshold voltage and the data voltage held to the capacitor part and applies the voltage to the driving transistor. Further, the switch part has a function which applies a constant voltage to the driving transistor before having the voltage containing the threshold voltage and the data voltage held to the capacitor part.