OLED Pixel Circuit Compensation for Feedthrough Voltage
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Solution Overview
Problem
In OLED display panels, the feedthrough voltage generated by switching transistors leads to non-uniform display due to parasitic capacitance and resistance differences along scan lines, causing variations in feedthrough voltages across pixels, resulting in display non-uniformity.
Innovation Solution
A pixel circuit is designed with a compensation unit, including a compensation capacitor, that reduces feedthrough voltage by transmitting a compensation voltage to the switching transistor, thereby minimizing voltage differences across pixels, using a compensation voltage terminal that can be shared with other power or initialization signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a switching transistor is used to transmit data voltage signal in OLED pixel circuit, then the pixel circuit can be controlled to display, but feedthrough voltage is generated causing display non-uniformity
Solution Approach 1:
The patent converts the harmful feedthrough voltage effect into a beneficial compensation mechanism. By intentionally introducing a compensation transistor that generates an equal and opposite feedthrough voltage, the harmful voltage variation is canceled out. The compensation transistor is designed with specific capacitance and resistance parameters to produce a compensating voltage that offsets the original feedthrough effect, thereby transforming the problem into a solution.
Solution Approach 2:
The compensation transistor acts as an intermediary element between the data voltage signal and the driving transistor gate. It introduces a compensating voltage signal that mediates the harmful feedthrough effect. This intermediary component processes the voltage signal by adding the compensation component, thereby eliminating the non-uniformity before it affects the OLED display output.
2Adaptability or versatility
If scan lines with resistance are used to control switching transistors, then pixel array can be addressed, but resistance differences cause variations in feedthrough voltages across pixels
Solution Approach 1:
The patent applies local quality by making each pixel circuit self-compensating through its local compensation transistor. Instead of requiring global uniformity across the entire scan line, each pixel independently generates its own compensation voltage tailored to its specific feedthrough conditions. This localized approach allows each pixel to correct its own voltage variations regardless of position in the array.
Solution Approach 2:
The compensation transistor creates a feedback mechanism where the gate-drain parasitic capacitance of the switching transistor is compensated by the gate-source parasitic capacitance of the compensation transistor. This feedback loop continuously counteracts the feedthrough voltage effect, ensuring that voltage variations are corrected in real-time during the pixel operation cycle.
Data Source
AI summary
A pixel circuit and a display device are provided. The pixel circuit includes: a driving transistor; a switching transistor for transmitting a data voltage signal to a first electrode of the driving transistor; a storage capacitor having a first terminal coupled to a control electrode of the driving transistor, and a second terminal coupled to a reference voltage terminal; a threshold voltage extraction unit for coupling the control electrode of the driving transistor to a second electrode of the driving transistor through the scan signal; a light emission control unit for transmitting a second power voltage to the first electrode of the driving transistor; a light emitting device having a first electrode coupled to a second electrode of the driving transistor and a second electrode receiving a first power voltage; a compensation unit for transmitting a compensation voltage to a second electrode of the switching transistor.