OLED Display Interlaced Scanning and Reverse Bias Circuit
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Solution Overview
Problem
Organic light emitting displays face challenges in ensuring an operation margin for driving circuits when handling large-size panels, experiencing voltage drops (IR-drop) in power source lines, and suffering from degradation and non-uniform brightness due to space charge accumulation in pixel circuits.
Innovation Solution
The implementation of an interlaced scanning method that divides the data write period from the light emission period, coupled with the application of a reverse bias voltage to organic light emitting diodes, and the use of a threshold voltage compensation circuit to manage semiconductor element variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If progressive scanning method is used, then image quality in static screen is improved, but operation margin of driving circuit cannot be ensured when driving large-size panel
Solution Approach 1:
The patent applies interlaced scanning method which divides the display into two fields (odd and even lines), scanning them alternately. This segmentation of the scanning process allows the driving circuit to operate with sufficient time margins by processing half the lines in each field period, thereby ensuring reliable operation in large-size panels while maintaining image quality.
2Illumination intensity
If progressive scanning method is used, then image quality is improved, but voltage drop (IR-drop) of first power source line VDD occurs
Solution Approach 1:
The interlaced scanning method divides the panel into two separate scanning fields (odd and even lines). By scanning only half the lines in each field period, the current draw from the first power source line VDD is reduced and distributed over time, preventing voltage drops and ensuring uniform brightness across the display.
3Illumination intensity
If current flows from anode to cathode of OLED, then light emission is achieved, but space charges are stored between HTL and EML or ETL and EML
Solution Approach 1:
The patent implements periodic application of reverse bias voltage to the OLED during non-light emission periods. This periodic reverse biasing clears accumulated space charges between the hole transport layer and emitting layer, or between electron transport layer and emitting layer, preventing current degradation and maintaining uniform brightness over time.
4Duration of action of stationary object
If reverse bias voltage is applied to OLED, then degradation is reduced and lifespan is increased, but additional circuit complexity is required
Solution Approach 1:
The patent combines the reverse bias application function with the existing emission control circuitry. The same control signals that manage light emission timing are used to coordinate reverse bias application during non-emission periods, merging multiple functions into existing circuit structures and minimizing additional complexity while extending OLED lifespan.
5Reliability
If interlaced scanning method is used, then operation margin is ensured and voltage drop is prevented, but scanning rate must be divided
Solution Approach 1:
The interlaced scanning method uses periodic action by alternating between odd and even field scanning. Although the overall frame rate is maintained, each individual field is scanned at a reduced rate, allowing sufficient time margins for driving circuit operation and voltage stabilization while still achieving the required overall refresh rate through the alternating field 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
This approach ensures an operation margin for driving circuits, prevents voltage drops, reduces organic light emitting diode degradation, and enhances the uniformity and longevity of pixel brightness by applying a reverse bias voltage during non-light emission periods.
Implementation Method 1
a current corresponding to a data voltage is supplied to the organic light emitting diode and thereby the organic light emitting diode emits light correspondingly to the supplied current
Implementation Method 2
applying a reverse bias voltage to the organic light emitting diode... as current flows in one direction from an anode to a cathode of the organic light emitting diode OLED, space charges are stored between a hole transport layer HTL and an emitting layer EML or between an electron transport layer ETL and an emitting layer EML
Data Source
AI summary
An organic light emitting display including a scan signal line forwarding a scan signal, a data line sending a data signal and a pixel coupled to the scan signal line and the data line, the organic light emitting diode display, wherein the pixel includes a first switching transistor transmitting a data signal from the data line in response to the scan signal of the scan signal line, a driving transistor, coupled to the first switching transistor, controlling driving current from a first power source line, a storage capacitor coupled between the driving transistor and the first power source line, an organic light emitting diode, coupled between the driving transistor and a second power source line, displaying an image with the driving current controlled by the driving transistor, an initial switching transistor, coupled between the storage capacitor and an initial power source line, initializing the storage capacitor, and a switching transistor for applying a reverse bias, coupled between the second power source line and the initial power source line, applying a reverse bias voltage to the organic light emitting diode.