OLED Pixel Capacitor Current Supply for TFT Variation Compensation
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Solution Overview
Problem
Amorphous-Silicon and poly-Silicon backplane technologies in AMOLEDs face issues with TFT stability and uniformity, leading to threshold voltage variations that result in image quality degradation and reduced panel lifespan due to the digital driving method's high current stress on OLEDs.
Innovation Solution
A light emitting pixel structure with a capacitor that supplies current based on the difference between two voltages, toggling these voltages for each light emitting period to maintain consistent current supply to OLEDs, independent of driving TFT characteristics, and a driving method that uses a switching circuit to control voltage supply based on scan and data signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a digital driving method is used to drive AMOLED panels, then the threshold voltage variations of TFTs can be compensated and image quality can be maintained, but the current stress on OLEDs increases significantly reducing their lifespan
Solution Approach 1:
The patent applies periodic action by dividing the frame into multiple sub-frames and further into sub-sub-frames, with each OLED being driven in alternating periods. Each OLED is turned on for a specific period then turned off, creating a periodic driving pattern that reduces cumulative current stress while maintaining display quality through the accumulation of light emission over multiple periods.
Solution Approach 2:
The patent segments the driving period into multiple sub-frames and sub-sub-frames, assigning different driving patterns to different OLEDs within the same pixel structure. This segmentation allows each OLED to receive reduced current during specific periods while others are active, thereby reducing the current stress on individual OLEDs and extending their operational lifespan.
2Manufacturing precision
If TFT characteristics vary due to manufacturing processes, then manufacturing complexity increases, but using conventional driving methods cannot compensate for these variations leading to image quality degradation
Solution Approach 1:
The patent implements feedback mechanisms through storage capacitors that store voltage levels corresponding to different gray scales, and through the digital driving method that adjusts driving parameters based on detected OLED characteristics. This feedback allows the system to compensate for TFT characteristic variations and maintain consistent image quality despite manufacturing variations.
Solution Approach 2:
The patent changes driving parameters dynamically by adjusting the number of sub-sub-frames, the timing of voltage application, and the intensity of current pulses based on the detected characteristics of each OLED and TFT. This parameter adjustment allows compensation for manufacturing variations and maintains consistent display quality across different devices.
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 uniform output and extended OLED lifespan by reducing stress on OLEDs and maintaining constant brightness, as the light emitting pixel consistently supplies current regardless of TFT degradation.
Implementation Method 1
a capacitor (130) having a first electrode (131) and a second electrode (132), and configured to supply a current to the organic light emitting diode (140) based on a voltage difference between the first electrode (131) and the second electrode (132)
Implementation Method 2
an organic light emitting diode (140) having an anode connected to the first electrode (131) and a cathode connected to a second power supply (150), and configured to emit light in response to a current supplied by the capacitor (130)
Data Source
AI summary
A light emitting pixel includes a first organic light emitting diode (OLED) and a capacitor supplying to the first OLED current generated by an electric charge corresponding to a difference between a first voltage supplied to a first electrode of the capacitor and a second voltage supplied to a second electrode of the capacitor. The light emitting pixel further include a second OLED to supply the first voltage to the first electrode. The light emitting pixel further includes a voltage supply device to supply the first voltage to the first electrode in response to the second voltage.