OLED Pixel Circuit for Brightness Uniformity via Threshold Compensation
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Solution Overview
Problem
Conventional organic light emitting displays face challenges in achieving uniform brightness due to variations in threshold voltage of driving transistors, leading to inconsistent light emission across pixels, and existing solutions complicate the process with increased wiring complexity and reliability issues.
Innovation Solution
A pixel design that minimizes wiring lines by incorporating specific transistors and capacitors to control current and voltage, including a first transistor for current control, a second transistor turned on with the fourth transistor for extended periods, and additional transistors for emission control, along with a demultiplexer to compensate for threshold voltage and supply data signals efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If additional transistors are added to compensate for threshold voltage variations, then uniform brightness is improved, but device complexity increases
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks: a first transistor block for current control, a second transistor block for data signal storage, and a third transistor block for emission control. This segmentation allows each block to perform its specific function independently, achieving uniform brightness through coordinated operation while maintaining manageable circuit complexity
Solution Approach 2:
The storage capacitor serves multiple functions: it stores data signals during the data signal period, provides voltage to the first transistor during the emission control period, and enables threshold voltage compensation. This multi-functionality reduces the need for additional separate components, balancing brightness uniformity with device complexity
2Manufacturing precision
If multiple wiring lines are coupled to the pixel, then threshold voltage compensation is improved, but process complexity increases
Solution Approach 1:
The first scan line and second scan line are merged into a single wiring line that provides both scan signals and data signals. The storage capacitor is merged with the data line to serve as both a signal storage element and a voltage source. This merging reduces the number of separate wiring lines and simplifies the manufacturing process while maintaining compensation functionality
Solution Approach 2:
The storage capacitor is charged with data signals in advance during the data signal period before the emission control period begins. This preliminary action ensures that the necessary voltage is already available for threshold voltage compensation during the emission control period, eliminating the need for additional real-time compensation wiring
3Measurement precision
If more transistors are added to control emission, then brightness control precision is improved, but reliability deteriorates
Solution Approach 1:
The third transistor is dynamically controlled based on the emission control signal, allowing precise control of the emission period. The transistor switches between conductive and non-conductive states in response to the emission control signal, enabling precise brightness control while maintaining reliable operation through clear on/off states
Solution Approach 2:
The third transistor acts as an intermediary between the emission control signal and the OLED emission. It receives the emission control signal and translates it into precise current control for the OLED, providing a reliable and controllable interface that improves brightness control precision without compromising reliability
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
The solution enables uniform brightness across pixels by compensating for threshold voltage variations and reducing process complexity, improving reliability and efficiency in organic light emitting displays.
Implementation Method 1
The organic light emitting display displays images using organic light emitting diodes (OLED) that generate light by re-combination of electrons and holes
Implementation Method 2
the storage capacitor Cst charges with the voltage corresponding to the data signal
Data Source
AI summary
A pixel capable of displaying an image with uniform brightness, the pixel including an organic light emitting diode, a first transistor to control an amount of current supplied from a first power source coupled to a first electrode to the OLED, a second transistor coupled between a data line and a third node to be turned on when a first scan signal is supplied to a first scan line, a first capacitor coupled between the gate electrode of the first transistor and a second node, a sixth transistor coupled between the second node and the third node to be turned off when an emission control signal is supplied to an emission control line, a second capacitor coupled between the third node and the first power source, a fifth transistor coupled between the first power source and the second node to be turned on when the first scan signal is supplied to the first scan line, and a fourth transistor coupled between a second electrode of the first transistor and the data line to be turned on when a second scan signal is supplied to a second scan line.