OLED Pixel Compensation for Threshold Voltage Shift
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Organic light emitting display apparatuses experience a shift in transistor threshold voltage towards positive polarity at high temperatures, leading to increased leakage current and decreased luminance, resulting in display defects like crosstalk when operated for extended periods.
Innovation Solution
A pixel unit with a compensation voltage system, where transistors have an additional electrode connected to a compensation line that applies a voltage to counteract the threshold voltage shift at high temperatures, and a temperature sensor and voltage generator to determine when to apply this compensation, ensuring optimal operation by floating the electrode at normal temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the organic light emitting display apparatus is operated for a long time, then the operation temperature increases, but the threshold voltage of transistors shifts toward positive polarity causing increased leakage current and decreased luminance
Solution Approach 1:
The patent applies parameter changes by introducing a compensation voltage that dynamically adjusts the threshold voltage of transistors based on temperature conditions. When temperature exceeds a reference level, the compensation voltage modifies the gate voltage of affected transistors to counteract the positive shift in threshold voltage, thereby maintaining stable operation over extended periods despite temperature-induced parameter drift
Solution Approach 2:
The patent implements feedback through a temperature sensing mechanism that continuously monitors the operation temperature and triggers compensation actions when the temperature exceeds a reference level. The compensation voltage is applied selectively based on this feedback, creating a closed-loop control system that maintains threshold voltage stability only when needed, thus resolving the contradiction between extended operation duration and threshold voltage stability
2Reliability
If a compensation voltage is applied to transistors at high temperature, then the threshold voltage is stabilized, but the device complexity increases due to additional electrodes and control circuits
Solution Approach 1:
The patent applies local quality by adding the fourth electrode and compensation voltage mechanism only to specific transistors (first and third transistors) that are most affected by temperature-induced threshold voltage shifts, rather than uniformly modifying all transistors in the pixel circuit. This selective approach stabilizes threshold voltage where needed while minimizing the increase in device complexity
Solution Approach 2:
The patent implements partial action by applying the compensation voltage only when the temperature exceeds a reference level, rather than continuously. The temperature sensing unit triggers the compensation mechanism selectively, ensuring threshold voltage stability is maintained during high-temperature operation while avoiding unnecessary complexity activation during normal temperature conditions
3Reliability
If the fourth electrode is always connected to compensation voltage, then threshold voltage is continuously compensated, but power consumption increases and normal operation is disrupted at low temperatures
Solution Approach 1:
The patent applies periodic action by intermittently activating the compensation voltage based on temperature conditions. The temperature sensing unit monitors temperature and triggers the compensation mechanism only when the temperature exceeds a reference level, creating a conditional periodic operation pattern that maintains threshold voltage stability during high-temperature periods while consuming minimal power during normal temperature operation
Solution Approach 2:
The patent implements dynamics by making the compensation voltage application adaptive and conditional rather than static. The fourth electrode's connection state dynamically changes based on temperature feedback - connected to compensation voltage when temperature exceeds the reference level, and disconnected (floated) when temperature is within normal range, thereby optimizing both reliability and power consumption across different operating conditions
Data Source
AI summary
A pixel unit of a display device including: an OLED; a first transistor including a first electrode connected to a first node, a second electrode connected to a second node, and a third electrode connected to a third node; a capacitor including a first electrode receiving a power voltage and a second electrode connected to the first node; a second transistor including a first electrode receiving a scan signal, a second electrode receiving a data voltage and a third electrode connected to the second node; a third transistor including a first electrode receiving the scan signal, a second electrode connected to the first node and a third electrode connected to the third node, wherein at least one of the first and third transistors includes a fourth electrode, the fourth electrode receives a compensation voltage when an operation temperature is above a preset temperature and is floated when the operation temperature is equal to or more than the preset temperature.