OLED Pixel Circuit with Initialization Transistor for Brightness Uniformity
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Solution Overview
Problem
Conventional organic light emitting displays face issues with non-uniform brightness due to threshold voltage shifts in pixels, affecting gray scale representation and leading to afterimages, as the voltage charged in storage capacitors is influenced by previous frame periods.
Innovation Solution
The proposed solution involves a pixel structure with multiple transistors and capacitors, including a storage capacitor, a first transistor for controlling current flow, and additional transistors for initializing and registering data signals, allowing for independent voltage charging and emission control, enabling uniform brightness across frames.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a conventional pixel structure with a storage capacitor is used, then the pixel can maintain voltage for light emission, but the threshold voltage of the driving transistor shifts due to voltage applied in previous frame periods, causing non-uniform brightness and afterimages
Solution Approach 1:
The pixel circuit is divided into multiple independent transistor components (first transistor for current control, second transistor for data signal registration, third transistor for scan signal response, fourth transistor for initialization). This segmentation allows each transistor to perform a specific function independently, preventing threshold voltage shifts from affecting overall brightness uniformity.
Solution Approach 2:
The fourth transistor initializes the first node before data signals are registered in the current frame period. By performing initialization in advance (in response to scan signals from previous frame), the circuit eliminates residual voltage effects from previous frames, ensuring that the storage capacitor charges to the correct voltage level without influence from prior gray scale values.
2Measurement precision
If the storage capacitor charges voltage based on data signals, then the pixel displays gray scales corresponding to data signals, but the gray scale in the current frame period is affected by the gray scale in the previous frame period
Solution Approach 1:
The fourth transistor performs initialization of the first node in advance, before data signals are registered. This preliminary action ensures that the starting voltage level is reset based on previous frame scan signals, preventing carryover effects from previous gray scale values and ensuring accurate gray scale representation in the current frame.
Solution Approach 2:
The third transistor responds to scan signals supplied through scan lines to control the charging of the storage capacitor. The circuit uses feedback from the scan signal timing to regulate when voltage is charged, ensuring that each frame's gray scale is determined independently by the current frame's data signals rather than being influenced by previous frame states.
3Reliability
If additional transistors are added to the pixel structure for initialization and data registration, then uniform brightness can be achieved, but the device complexity increases
Solution Approach 1:
The third transistor serves multiple functions: it responds to scan signals to enable data signal registration, controls the charging of the storage capacitor, and works in conjunction with the fourth transistor for initialization. By making this transistor multi-functional, the circuit achieves brightness uniformity with minimal additional components.
Solution Approach 2:
The initialization function and data registration function are merged into a coordinated sequence controlled by the same scan signals. The fourth transistor handles initialization while the second and third transistors handle data registration, with both operations timed together through the scan signal sequence, reducing the need for separate dedicated circuits.
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 allows for the display of images with uniform brightness by isolating the impact of previous frame periods on current frame brightness, preventing afterimages and ensuring consistent gray scale representation.
Implementation Method 1
The organic light emitting display has high response speed and is driven with low power consumption. The organic light emitting display display images use organic light emitting diodes (OLED) that generate light by re-combination of electrons and holes.
Data Source
AI summary
In an organic light emitting display including a pixel, and a method of driving the same, the pixel includes an organic light emitting diode (OLED), a storage capacitor coupled between a first power supply and a first node, a first transistor for controlling a current that flows from the first power supply to a second power supply through the OLED in response to a voltage applied to the first node, a second transistor coupled between a data line and a first electrode of the first transistor and turned on when a control signal is supplied through a control line, a third transistor coupled between the first node and a second electrode of the first transistor and turned on when a scan signal is supplied through an nth (n is a natural number) scan line, and a fourth transistor coupled between an initializing power supply and the first node and turned on when the scan signal is supplied through an (n−1)th scan line.