OLED Pixel Circuit Simplification via Scan Driver Extraction
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Solution Overview
Problem
Conventional organic light emitting displays face challenges in achieving uniform luminance due to variations in threshold voltage of transistors and require additional transistors for controlling current supply time, making it difficult to display images with uniform grey levels and proper white balance.
Innovation Solution
The proposed solution involves a pixel circuit with an organic light emitting diode, a first transistor connected to scan and data lines, a storage capacitor connected to a reset line, and a second transistor that controls current flow based on storage capacitor voltage, with the ability to turn off when a reset signal is supplied, allowing for digital driving mode and simplified configuration without additional transistors for light emission control. Additionally, a scan driver and data driver synchronize signals to control light emission periods and white balance by adjusting reset signal times for red, green, and blue pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional pixel circuit configuration with multiple transistors is used to control current supply time, then light emission control capability is improved, but device complexity increases
Solution Approach 1:
The patent extracts the light emission control function from the traditional multi-transistor pixel circuit and relocates it to the scan driver circuit. By removing the dedicated emission control transistor from each pixel, the patent simplifies the pixel circuit while centralizing the control logic in the scan driver, thereby reducing overall device complexity without sacrificing control capability
Solution Approach 2:
The scan driver circuit is designed to perform multiple functions: it generates scan signals for sequential pixel activation, controls light emission timing through the emission control signal, and manages reset operations. This multi-functional approach eliminates the need for separate dedicated control transistors in each pixel circuit
2Ease of operation
If additional transistors are added to control current supply time, then light emission timing control is improved, but manufacturing precision requirements increase
Solution Approach 1:
By extracting the emission timing control function from the pixel circuit transistors and placing it in the scan driver, the patent eliminates the need for precise threshold voltage matching in additional transistors. The scan driver operates at a higher level where timing control is achieved through signal timing rather than transistor parameter matching
Solution Approach 2:
The patent introduces an emission control signal as an intermediary mechanism between the scan driver and the pixel circuit. This signal acts as a mediator that controls the timing of current supply to the OLED without requiring additional transistors with precise threshold voltage characteristics within the pixel circuit itself
3Device complexity
If simplified pixel circuit is used, then device complexity is reduced, but white balance control capability deteriorates
Solution Approach 1:
The emission control signal serves as an intermediary that enables white balance control at the driver level rather than requiring complex pixel circuit modifications. By adjusting the timing and duration of this intermediary signal, the scan driver can control the light emission periods of different color sub-pixels to achieve proper white balance
Solution Approach 2:
The patent employs periodic emission control signals with adjustable duty cycles to control the light emission periods of red, green, and blue sub-pixels differently. This periodic action allows the simplified pixel circuit to achieve white balance control by varying the on-time of each color channel according to their respective luminance 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 enables uniform luminance and simplifies the pixel circuit, allowing for efficient digital driving and improved white balance by controlling light emission periods and durations based on the color of the pixels, effectively addressing the challenges of threshold voltage variations and white balance issues.
Implementation Method 1
an organic light emitting display displays an image using an organic light emitting diode which generates light by means of recombination of electrons and holes
Data Source
AI summary
A pixel of a simplified configuration, and an organic light emitting display using the same are disclosed. The pixel includes an organic light emitting diode; a first transistor connected with a scan line and a data line and turned on when a scan signal is supplied to the scan lines; a storage capacitor having one terminal connected to an electrode of the first transistor and the other terminal connected to a reset line; and a second transistor for controlling an electric current that flows from a first power source to a second power source through the organic light emitting diode according to a voltage charged in the storage capacitor, wherein the second transistor is turned-off when a reset signal is supplied to the reset line.