N-channel pixel circuits for stable organic EL displays
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Solution Overview
Problem
Existing active matrix organic electroluminescence (EL) display devices face challenges with large-scale production due to high load on driving circuits caused by pulse-driving of common lines, limited flexibility in using different types of transistors, and inefficiencies in power management, particularly with amorphous silicon thin-film transistors.
Innovation Solution
The implementation of pixel circuits with N-channel transistors, a holding capacitor, a writing switch, a detection trigger line, and a detection trigger capacitor, along with an enable switch and a separation switch, allows for efficient current control and voltage regulation, enabling the use of both enhancement-type and depletion-type transistors and reducing power loss by eliminating series connections with the organic EL elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pulse-driving is applied to common lines to display stable images, then image stability is improved, but the driving circuit load increases significantly
Solution Approach 1:
The patent divides the common line driving function into individual transistor gate control lines, eliminating the need for pulse-driving common lines. Each transistor's gate is controlled independently through dedicated control lines, which segments the driving function and avoids the large capacitive discharge current problem of pulse-driving shared common lines.
Solution Approach 2:
The patent changes the voltage parameter applied to transistor gates dynamically through control lines, allowing precise control of transistor conduction states without requiring pulse-driving of common lines. This parameter change approach enables stable image display with reduced driving circuit load.
2Ease of operation
If enhancement-type transistors with positive threshold voltage are used, then circuit operation is simplified, but flexibility in manufacturing is reduced
Solution Approach 1:
The patent designs the pixel circuit to be universally compatible with both enhancement-type and depletion-type transistors. The control line configuration and switching mechanism work effectively with either transistor type, allowing manufacturers to choose based on process capabilities without redesigning the circuit architecture.
Solution Approach 2:
The patent employs dynamic control of transistor gates through control lines that can adapt the circuit operation to different transistor types. The control mechanism dynamically adjusts voltage application timing and levels to accommodate the different threshold voltage characteristics of enhancement-type and depletion-type transistors.
3Adaptability or versatility
If series connections are used with organic EL elements, then circuit functionality is enhanced, but power loss increases
Solution Approach 1:
The patent extracts the light-emitting function into separate organic EL elements that are connected in parallel rather than in series with other circuit components. This extraction eliminates unnecessary series connections that would cause voltage drops and power loss, while maintaining full circuit functionality through the parallel architecture and control line system.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances the flexibility and efficiency of large-scale organic EL display devices by isolating the organic EL elements from other components, reducing power loss, and maintaining image stability despite changes in threshold voltage over time.
Implementation Method 1
a detection trigger capacitor for supplying a voltage to change a source voltage of the driver transistor
Implementation Method 2
a holding capacitor for holding a voltage that determines an amount of the electric current supplied from the driver transistor
Implementation Method 3
organic electroluminescence (EL) display devices... current-driven type light-emitting elements... self-luminous organic EL elements
Data Source
AI summary
An image display device having a plurality of pixel circuits arranged in matrix, each comprising current-driven type light-emitting element, driver transistor for supplying a current to current-driven type light-emitting element, holding capacitor for holding a voltage that determines an amount of the current supplied from driver transistor, and writing switch for writing a voltage corresponding to an image signal into holding capacitor. The transistor formed in each pixel circuit is N-channel transistor. Each pixel circuit further comprises detection trigger line and detection trigger capacitor for supplying a voltage to change a source voltage of driver transistor. One terminal of detection trigger capacitor is connected to a source of driver transistor and the other terminal of detection trigger capacitor is connected to detection trigger line.