OLED Pixel Compensation Circuit for Brightness Deterioration
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Solution Overview
Problem
Conventional organic light emitting display devices suffer from reduced brightness over time due to the deterioration of organic light emitting diodes, which affects the display's ability to maintain desired image brightness.
Innovation Solution
The implementation of a compensation unit within each pixel, comprising a second transistor and a capacitor serially coupled between the gate and source electrode of a drive transistor, which adjusts the voltage to compensate for diode deterioration by sharing charge between initialization and data voltages, thereby increasing the current supplied to the organic light emitting diode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional pixel circuit without compensation unit is used, then device complexity is low, but brightness decreases over time due to diode deterioration
Solution Approach 1:
The compensation unit performs preliminary measurement of the voltage drop across the OLED during the initialization phase, before the actual display data is written. This advance measurement allows the system to pre-calculate and store the compensation value in the capacitor, so that when the display data is applied, the gate voltage already includes the necessary compensation to maintain correct brightness despite diode deterioration.
Solution Approach 2:
The compensation unit acts as an intermediary between the data driver and the OLED. It measures the actual voltage drop across the OLED, calculates the difference from the expected voltage, and adds this compensation value to the gate voltage before it reaches the OLED. This intermediary measurement and adjustment mechanism ensures that deteriorated OLEDs receive compensated drive voltage to maintain proper brightness.
2Reliability
If compensation unit with second transistor and capacitor is added, then brightness compensation is achieved, but manufacturing complexity increases
Solution Approach 1:
The pixel circuit is segmented into distinct functional blocks: the original drive transistor, the compensation unit (with its own transistor and capacitor), and the storage capacitor. This segmentation allows each component to be independently designed, sized, and positioned, making it easier to integrate into existing manufacturing processes and to optimize the layout for mass production while maintaining the compensation functionality.
3Illumination intensity
If higher current is supplied to compensate for deterioration, then brightness is maintained, but power consumption increases
Solution Approach 1:
The compensation unit implements a feedback mechanism by continuously measuring the actual voltage drop across the OLED and using this information to adjust the gate voltage. This feedback loop ensures that current is increased only to the extent necessary to compensate for measured deterioration, rather than using a fixed high current that would waste power. The system dynamically adjusts current based on actual diode performance.
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 solution effectively compensates for the brightness decrease caused by diode deterioration, maintaining the display's brightness by increasing the current flowing through the organic light emitting diode, thus extending the device's operational lifespan.
Implementation Method 1
organic light emitting diodes, which generate light by recombination of electrons and holes
Implementation Method 2
a compensation unit coupled between the gate electrode and a source electrode of the second transistor, the compensation unit configured to control voltage at the gate electrode of the second transistor
Data Source
AI summary
An organic light emitting display device that is capable of compensating for deterioration of organic light emitting diodes includes: a scan driver driving scan lines, compensation control lines, and light emission control lines; a data driver supplying initialization voltage to data lines during a first subperiod of a horizontal period and supplying data signals to the data lines during a second subperiod of the horizontal period; and pixels positioned at crossing areas of the scan lines and the data lines. Each pixel includes: an organic light emitting diode; a pixel circuit including a driving transistor controlling current flowing through the organic light emitting diode; and a compensation unit adjusting voltage of the gate electrode of the driving transistor based on deterioration of the organic light emitting diode. The compensation unit includes a transistor and a capacitor serially coupled between the gate and source of the driving transistor.