Pixel Circuit Initialization for OLED Display Uniformity
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Solution Overview
Problem
In display devices, particularly those using a 4T-1C structure with p-channel metal oxide semiconductor transistors, the lack of anode voltage initialization in pixels leads to increased non-emission time, reduced power supply stability, luminance deviation, and image uniformity issues due to sequential data writing and emission methods.
Innovation Solution
A display device with a pixel structure including a first transistor, a driving transistor, a second transistor, a third transistor, a fourth transistor, and an organic light emitting diode, where the fourth transistor, connected in parallel with the driving transistor, receives an initialization signal to simultaneously initialize the anode voltage and gate voltage during an initialization period, allowing for simultaneous emission and reducing initialization time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a 4T-1C structure with PMOS transistors is used for simultaneous emission display, then the pixel structure is simplified compared to 7T-1C progressive emission, but the anode voltage cannot be initialized leading to luminance deviation and image uniformity deterioration
Solution Approach 1:
The pixel circuit is segmented into multiple functional blocks: a driving transistor for current control, a fourth transistor specifically for anode voltage initialization, a storage capacitor for voltage holding, and other support transistors. This segmentation allows the initialization function to be independently implemented without redesigning the entire pixel structure, thus maintaining simplicity while improving image uniformity.
Solution Approach 2:
The fourth transistor is configured to initialize the anode voltage of the OLED before the emission period begins. By performing this initialization action in advance (during the initialization period), the circuit ensures stable operating conditions for subsequent data writing and emission, preventing luminance deviation caused by unstable anode voltage.
2Ease of manufacture
If sequential data writing is used to write pixel data, then the data writing process is simple, but the initialization time increases and power supply stability decreases
Solution Approach 1:
The circuit performs anode voltage initialization through the fourth transistor before the sequential data writing process begins. This preliminary action ensures that when data writing starts, the anode voltage is already stable, thereby reducing the total time required for proper pixel initialization without complicating the sequential data writing approach.
Solution Approach 2:
The pixel circuit self-initializes its anode voltage using the fourth transistor and storage capacitor configuration. This self-service mechanism eliminates the need for external initialization circuits or extended initialization periods, allowing the circuit to prepare itself quickly before receiving sequential data writes.
3Device complexity
If the anode voltage is not initialized before emission, then the pixel structure remains simple, but power supply stability is reduced causing luminance deviation
Solution Approach 1:
The power supply stability function is segmented from the main driving circuit by introducing a dedicated fourth transistor and storage capacitor configuration. This separate initialization module stabilizes the anode voltage without interfering with the simplicity of the main pixel structure, achieving both goals simultaneously.
Solution Approach 2:
The fourth transistor initializes the anode voltage to a predetermined level before the emission period begins. This preliminary stabilization action ensures that subsequent power supply variations do not cause luminance deviation, as the anode voltage is already properly conditioned for stable operation.
4Device complexity
If a 4T-1C structure is used without anode voltage initialization, then fewer transistors are needed, but non-emission time increases and display reliability decreases
Solution Approach 1:
The display device is segmented into a 4T-1C pixel structure with an added initialization transistor (making it effectively a 5T-1C structure for initialization purposes). This segmentation allows the initialization function to be added with minimal impact on the overall transistor count and circuit complexity, while significantly improving display reliability.
Solution Approach 2:
The fourth transistor performs preliminary anode voltage initialization before the emission and data writing phases. This preliminary action reduces the non-emission time by eliminating voltage stabilization delays during emission, thereby improving display reliability without substantially increasing the transistor count or circuit complexity.
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 approach reduces initialization time, eliminates voltage deviation between the anode and gate voltages, and enhances image stability by using an NMOS transistor for initialization, preventing display failures and ensuring stable, flicker-free images.
Implementation Method 1
an organic light emitting diode connected between the second node and the second power
Data Source
AI summary
A pixel includes first to fourth transistors and a driving transistor. The first transistor is connected between a data line and a first node and has a gate electrode to receive a scan signal. The driving transistor is connected between the first node and a second node and has a gate electrode connected to a third node. The second transistor is connected between the second and third nodes and has a gate electrode to receive the scan signal. The third transistor is connected between first power and the first node and has a gate electrode to receive an emission signal. The fourth transistor is connected between the first and second nodes and has a gate electrode to receive an initialization signal. An organic light emitting diode is connected between the second node and second power. A storage capacitor is connected between the first power and third node.