OLED Pixel Circuit Stabilizing Luminance via Dual Voltage Storage
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Solution Overview
Problem
Conventional organic light emitting displays face challenges in achieving desired luminance and gray scale expression due to variations in threshold voltage and mobility of driving transistors, which affect image quality and the ability to display low-level gray scales.
Innovation Solution
The proposed solution involves a pixel configuration with specific transistor and capacitor arrangements that control current and voltage signals to stabilize voltage charging and emission time, allowing for improved gray scale expression and luminance control, independent of transistor variations. This includes a scan driver, data driver, current sink unit, and pixel circuit with transistors and capacitors that manage scan and data signals to control the organic light emitting diode's light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional driving methods are used, then the display can operate, but the luminance and gray scale expression are unstable due to transistor variations
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks: a first transistor for current control, a second transistor for voltage storage, a third transistor for switching, and multiple capacitors for voltage storage. This segmentation allows independent optimization of current control and voltage storage functions, compensating for transistor parameter variations and achieving stable luminance and precise gray scale expression.
Solution Approach 2:
The patent changes the operating parameters of the pixel circuit by introducing dual voltage storage devices and multiple switching transistors that control the charging and discharging timing. This allows precise control of the emission time and voltage levels applied to the OLED, enabling accurate gray scale expression independent of transistor threshold voltage variations.
2Manufacturing precision
If simple pixel circuits are used, then the device complexity is low, but the ability to control emission time and voltage precisely is insufficient
Solution Approach 1:
The pixel circuit performs preliminary actions by storing voltages in advance in two separate capacitors before the emission period. The first capacitor stores a voltage related to the data signal, and the second capacitor stores a voltage that will be combined with the first. This preliminary voltage storage and combination enables precise control of the final emission voltage and timing without requiring complex real-time control circuits.
3Reliability
If transistor variations are not compensated, then the circuit is simple, but the image quality and luminance uniformity deteriorate
Solution Approach 1:
The pixel circuit implements a feedback mechanism where the stored voltages in the capacitors are combined and applied to control the OLED emission. The circuit structure ensures that the final emission level depends on the stored voltages rather than the instantaneous transistor parameters, providing natural compensation for transistor variations and improving image quality and luminance uniformity across the 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
The solution enables stable voltage charging and precise control over emission time, enhancing gray scale expression and luminance, thus improving the overall image quality and ability to display desired luminance levels, regardless of transistor variations.
Implementation Method 1
organic light emitting displays are configured to display images using organic light emitting diodes that emit light through recombination of electrons and holes
Data Source
AI summary
An organic light emitting display includes a scan driver, a data driver, a current sink unit, and pixels. The scan driver is configured to provide a first scan signal to first scan lines and a second scan signal to second scan lines. The data driver is configured to provide a data signal to first data lines and a voltage data signal to second data lines. The current sink unit is configured to provide a current data signal to third data lines. The pixels are configured to store a voltage corresponding to the voltage data signal and the current data signal. A light emission time of the pixels is controlled by the data signal.