Three-Transistor Pixel Circuit for OLED Threshold Voltage Compensation
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Solution Overview
Problem
Active matrix organic electroluminescence (EL) display devices face issues with luminance unevenness due to variation in threshold voltage of drive transistors, and existing methods either require a large number of transistors or suffer from crosstalk and power line voltage drops with increased screen size.
Innovation Solution
A display device configuration using three transistors per pixel, including a first switching transistor, a drive transistor, and a reset transistor, along with a capacitor element, to detect and compensate the threshold voltage without scanning the power source line, allowing for even luminance across the screen.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If four transistors per pixel are used for threshold voltage detection, then threshold voltage compensation is achieved, but manufacturing yield decreases due to increased transistor integration complexity
Solution Approach 1:
The patent extracts the threshold voltage detection function from a separate four-transistor circuit and integrates it into the existing three-transistor pixel structure by utilizing the gate line voltage as a reference, thereby eliminating the need for an additional transistor while maintaining compensation capability
Solution Approach 2:
The gate line is given multiple functions: it serves as both the control signal for the switching transistor and the reference voltage source for threshold voltage detection, allowing the same circuit element to perform both display control and compensation functions
2Productivity
If three transistors per pixel are used, then productivity is improved, but crosstalk occurs due to one-dimensional power source line wiring
Solution Approach 1:
The patent transitions from one-dimensional power source line wiring to two-dimensional wiring by connecting the other end of the capacitor element to the gate line through the reset transistor, creating a planar configuration that prevents voltage drops and eliminates crosstalk while maintaining high productivity
3Measurement precision
If power source line scanning is performed, then threshold voltage detection is enabled, but screen size expansion is limited due to voltage drop
Solution Approach 1:
The capacitor element acts as an intermediary that stores the threshold voltage detected at one location and makes it available at the drain terminal of the switching transistor, enabling accurate threshold voltage detection without requiring power source line scanning across the entire display
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 compensates for threshold voltage variations, reducing luminance unevenness and enabling larger screen sizes without the need for extensive power line scanning, thus improving display uniformity and productivity.
Implementation Method 1
a capacitor element having one end connected to the gate terminal of the drive transistor, and an other end connected to the one of the source terminal and the drain terminal of the drive transistor
Implementation Method 2
a luminescence element which produces luminescence according to a flow of current
Data Source
AI summary
A display device includes luminescence pixels arranged in rows and columns. Each of gate lines and reset lines correspond to one of the rows, and signals lines each correspond to one of the columns. Each luminescence pixels includes a luminescence element, a switching transistor, a drive transistor which supplies current to the luminescence element, and a reset transistor. The reset transistor includes a gate terminal connected to a corresponding reset line, one of a source and drain terminal connected to a source or drain terminal of the drive transistor, and the other of the source and drain terminal connected to a corresponding gate line. A capacitor is connected between the gate terminal and the source terminal of the drive transistor.