OLED Pixel Compensating Circuit Leakage Control
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Solution Overview
Problem
Existing pixel compensating circuits for OLED displays face issues with electrical current leakage at low display grayscales, leading to poor contrast and irregular voltages due to threshold voltage drift in driving transistors, which affects display quality.
Innovation Solution
A pixel compensating circuit comprising specific transistor connections and a storage capacitor, where the drain voltage of the first transistor is set to be less than or equal to the sum of a reference voltage and the threshold voltage of the compensating transistor, ensuring the organic light-emitting diode only illuminates when the voltage difference exceeds a certain threshold, preventing leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the driving transistor threshold voltage is allowed to drift, then the circuit complexity is reduced, but the display quality deteriorates due to unstable driving current
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage compensation before the OLED illumination phase. The compensating transistor T21 and storage capacitor Cst are used to pre-adjust the gate voltage of the driving transistor T2, ensuring that the threshold voltage drift is compensated in advance. This allows the driving current to remain stable despite threshold voltage variations, resolving the contradiction between circuit simplicity and display quality.
2Use of energy by moving object
If the voltage difference across the OLED is reduced to achieve low grayscale display, then the power consumption is reduced, but electrical current leakage occurs leading to poor contrast
Solution Approach 1:
The patent introduces the compensating transistor T21 as an intermediary element between the data signal input and the driving transistor gate. This compensating transistor, controlled by the scan signal SCAN(n), acts as a mediator to precisely adjust the gate voltage of the driving transistor T2. By using this intermediary, the circuit can achieve low grayscale display with reduced voltage difference while preventing leakage currents, thus maintaining good contrast without increasing power consumption.
3Reliability
If the threshold voltage compensation is implemented, then the driving current stability is improved, but the device complexity increases due to additional transistors and capacitors
Solution Approach 1:
The patent applies universality by designing the compensating transistor T21 to serve multiple functions: it acts as a switch controlled by the scan signal, performs threshold voltage compensation, and works with the storage capacitor Cst to maintain the compensated gate voltage. This multi-functional design allows threshold voltage compensation to be achieved with minimal additional components, reducing the impact on device complexity while improving driving current stability.
Data Source
AI summary
A pixel compensating circuit comprises an organic light-emitting diode (OLED), a first transistor, a compensating transistor, a storage capacitor, a second transistor, a third transistor, and a seventh transistor. If a present-stage scan signal is at a low voltage potential, the second transistor is turned on, the gate of the first transistor and the drain of the first transistor are short-circuited. A data signal is transmitted to a source of the first transistor after the third transistor is turned on. A third reference voltage is transmitted to the source of the first transistor after the seventh transistor is turned on. An aging phenomenon and the uniformity of the driving transistor are improved.