Pixel Circuit Initialization for Display Bright Spots and Black Floating
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Solution Overview
Problem
In organic EL display devices, the simultaneous occurrence of bright spots and black floating is a problem due to the use of the same initialization voltage for the gate terminal of the TFT and the anode terminal of the organic EL element, leading to either bright spots or black floating depending on the initialization voltage level.
Innovation Solution
A display device with a pixel circuit configuration where the gate terminal of the drive transistor and the anode terminal of the organic EL element are initialized to different voltage levels, using a specific transistor arrangement and initialization method to prevent both bright spots and black floating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the initialization voltage Vini is low, then the leakage current through TFT M91 increases, but the gate voltage of the drive transistor is reduced, causing the organic EL element to emit light and produce bright spots
Solution Approach 1:
The patent segments the initialization control into two independent transistors, allowing the drive transistor gate to be initialized with a voltage level optimized for preventing leakage current, while the organic EL element anode is initialized with a different voltage level optimized for preventing unintended light emission.
Solution Approach 2:
The patent changes the initialization voltage parameter from a single unified voltage to two distinct voltage levels: a first initialization voltage for the drive transistor gate and a second initialization voltage for the organic EL element anode. This parameter differentiation resolves the contradiction by allowing each voltage to be optimized for its specific function.
2Device complexity
If the same initialization voltage is used for both the gate terminal of the drive transistor and the anode terminal of the organic EL element, then the circuit configuration is simple, but either bright spots or black floating occurs depending on the voltage level
Solution Approach 1:
The patent introduces a second transistor (TFT M97) dedicated to initializing the organic EL element anode, separate from the first transistor (TFT M91) that initializes the drive transistor gate. This segmentation adds minimal circuit complexity while enabling independent voltage control to eliminate display defects.
Solution Approach 2:
The patent implements local quality control by applying different initialization voltages to different terminals: the first initialization voltage for the drive transistor gate terminal and the second initialization voltage for the organic EL element anode terminal. This local differentiation eliminates the need to compromise between conflicting voltage requirements.
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 effectively suppresses both bright spots and black floating by initializing the gate terminal of the drive transistor and the anode terminal of the organic EL element to distinct voltage levels, preventing layout area increase and maintaining image quality.
Implementation Method 1
The organic EL element is a kind of electro-optical element and emits light at brightness according to the amount of flowing current
Data Source
AI summary
A pixel circuit of a display device includes an electro-optical element, a drive transistor, a first transistor including a first conduction terminal connected to an anode terminal of the electro-optical element, a second conduction terminal to which an initialization voltage is applied, and a gate terminal connected to a scanning line, a second transistor including a first conduction terminal connected to a gate terminal of the drive transistor and a gate terminal connected to an immediately preceding scanning line selected in a horizontal interval immediately before the scanning line is selected, and a third transistor being diode-connected and including a drain terminal and a gate terminal to which an initialization voltage is applied and a source terminal connected to a second conduction terminal of the second transistor. Thus, a display device that can suppress both the bright spots and the black floating is provided.