OLED Pixel Circuit Initialization Voltage Control
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Solution Overview
Problem
Display devices with organic light-emitting diodes (OLEDs) face issues with current leakage, leading to a 'black spot' phenomenon where brightness increases during black gradation due to voltage being applied to the anode of light-emitting elements, causing unwanted light emission.
Innovation Solution
A display apparatus and pixel circuit design that controls voltage during initialization using a reference voltage and initialization voltage, applied to specific electrodes of a capacitor connected to the gate electrode of a driving transistor, to prevent current leakage and minimize black spot occurrences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage is applied to initialize the pixel circuit, then the pixel circuit is properly initialized, but current leakage occurs causing black spot phenomenon
Solution Approach 1:
The pixel circuit is divided into two independent initialization paths: one path (first initialization transistor) applies initialization voltage to the gate electrode of the driving transistor, and another path (second initialization transistor) applies reference voltage to the gate electrode of the emission transistor. This segmentation allows different voltage levels to be applied to different components simultaneously, preventing current leakage while maintaining proper initialization.
Solution Approach 2:
A capacitor is introduced as an intermediary component connected between the gate electrode of the driving transistor and the gate electrode of the emission transistor. The capacitor stores and transfers charge between these two nodes, enabling precise voltage control during initialization. By using the capacitor as a mediator, the circuit can maintain proper voltage levels without direct current paths that would cause leakage.
2Measurement precision
If reference voltage is applied to the gate electrode of the emission transistor, then voltage control is improved, but circuit complexity increases
Solution Approach 1:
The capacitor serves multiple functions: it acts as a charge storage element, a voltage transfer medium, and a coupling element between the driving transistor and emission transistor gates. By making the capacitor multi-functional, the circuit achieves precise voltage control without adding numerous separate components, thus limiting the increase in circuit complexity.
Solution Approach 2:
The gate electrode of the emission transistor is pre-charged to a reference voltage level before the emission phase through the second initialization transistor. This preliminary action ensures that the emission transistor is properly biased and ready for operation, improving voltage control precision without requiring complex real-time adjustment circuits.
Data Source
AI summary
A display apparatus includes a mode controller that generates a first and second control signals, a gate drive circuit that generates a light-emitting signal, a pixel circuit comprising a driving transistor, a first and second transistor that receives the first and control signals, a first light-emitting element connected to the first transistor, a second light-emitting element connected to the second transistor, a third transistor connected between the driving transistor and the first transistor and operates responsive to the light-emitting signal, and a capacitor connected to a gate electrode of the driving transistor, and a first and second lens on the first and second light-emitting elements, wherein in an initialization period of the pixel circuit, a reference voltage is applied to a first electrode of the capacitor and an initialization voltage is applied to a second electrode of the capacitor.