AMOLED Pixel Circuit Parameter Extraction and Compensation
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Solution Overview
Problem
Active Matrix Organic Light Emitting Diode (AMOLED) displays face issues with luminance non-uniformity due to electrical characteristic variations of drive transistors and image sticking due to differential aging of OLED devices, requiring effective methods to extract and compensate for pixel and OLED parameters.
Innovation Solution
A display system with pixel circuits comprising a drive transistor, storage capacitor, and light emitting device, where a controller drives the pixel circuit through multiple operation states, including programming and measurement states, using a readout circuit to integrate and convert current measurements into digital codes for parameter extraction and compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If drive transistors are used to control OLED devices in AMOLED displays, then the display can achieve active matrix control and high brightness, but electrical characteristic variations of drive transistors cause luminance non-uniformity
Solution Approach 1:
The patent applies preliminary action by measuring pixel circuit parameters (such as transistor threshold voltage and mobility) and OLED device parameters (such as leakage current and series resistance) before the display is put into normal operation. These measurements are stored and used to pre-calculate compensation values that are applied during programming, thereby compensating for manufacturing variations and aging effects before they cause visible defects like luminance non-uniformity
Solution Approach 2:
The patent implements feedback by using measured parameter values from pixel circuits and OLED devices to adjust programming voltages and currents. The readout circuit measures actual device characteristics, and this measurement feedback is used to modify the programming signals applied to pixel circuits, thereby compensating for deviations and maintaining luminance uniformity throughout the display's operational life
2Productivity
If OLED devices operate continuously to provide display output, then the display maintains image functionality, but differential aging of OLED devices causes image sticking
Solution Approach 1:
The patent applies preliminary action by continuously or periodically measuring OLED device parameters during operation to detect early signs of aging and differential degradation. By storing historical measurement data and comparing it against current measurements, the system can predict and compensate for aging effects before they manifest as visible image sticking, thereby maintaining image quality stability over the display's operational lifetime
Solution Approach 2:
The patent implements feedback by using the readout circuit to continuously monitor OLED device parameters and feed this information back to the controller. The controller uses this feedback to dynamically adjust programming voltages and currents for each pixel, compensating for differential aging effects and preventing image sticking while maintaining continuous display functionality
3Manufacturing precision
If parameter extraction and compensation methods are implemented, then luminance non-uniformity and image sticking are reduced, but the system requires additional measurement and control circuitry
Solution Approach 1:
The patent applies merging by integrating the readout circuit functionality directly into the existing pixel circuit structure. The same data lines and transistor components are used for both normal display operation and parameter measurement, combining multiple functions into a single integrated circuit architecture. This approach enables parameter extraction and compensation capabilities without adding separate dedicated measurement circuitry, thereby reducing the increase in device 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
Enables accurate extraction of pixel and OLED parameters, allowing for adjustments in programming voltages to maintain high image quality by compensating for degradation, thereby reducing luminance non-uniformity and image sticking in AMOLED displays.
Implementation Method 1
a light emitting device coupleable to the source terminal of the drive transistor
Implementation Method 2
Active Matrix Organic Light Emitting Diode (AMOLED) displays
Data Source
AI summary
Active Matrix Organic Light Emitting Diode (AMOLED) displays, novel pixel circuits therefor, and methods of programming the pixel circuit and measuring the current of the pixel circuit and OLED thereof are disclosed. One pixel circuit includes four TFT transistors, a storage capacitor and an OLED device and is programmed with use of voltage supplied through a data line. One method measures currents of the OLED and the pixel circuit through the data line by a readout circuit.