Pixel Circuit with Dual-Reset for AMOLED Flicker Reduction
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Solution Overview
Problem
The current AMOLED flexible screen technology faces issues with uneven brightness due to non-uniform threshold voltage of Driving Thin Film Transistors (DTFTs), leading to problems like flickering and afterimages, especially when switching between different driving frequencies, which affect the display effect.
Innovation Solution
A pixel circuit design incorporating a first reset transistor, compensation transistor, drive transistor, data writing transistor, light emitting control transistors, and a storage capacitor, along with a specific driving method that includes phases for initialization, data writing, and light emission, ensures uniform threshold voltage and reduced flickering by using P-type and N-type transistors made of low temperature poly-silicon and metal oxide semiconductor materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional pixel circuit with DTFT is used, then the display device can be manufactured, but the threshold voltage uniformity is poor causing uneven brightness
Solution Approach 1:
The patent applies preliminary action by resetting the second electrode of the drive transistor to a high level before data writing occurs. This pre-resetting action ensures that the threshold voltage is compensated uniformly across all pixels before the actual display data is written, thereby improving threshold voltage uniformity without complicating the manufacturing process. The reset phase precedes the data writing phase in the driving method, allowing uniform threshold voltage establishment.
2Reliability
If the DTFT operates without additional control, then the circuit is simple, but flickering and afterimage problems occur
Solution Approach 1:
The patent segments the light emission control into two independent transistors: the first light emitting control transistor controls the second electrode of the drive transistor, while the second light emitting control transistor controls the first electrode of the light emitting device. This segmentation allows independent control of different circuit nodes, enabling effective suppression of flickering and afterimage effects without requiring a complete redesign of the entire pixel circuit.
Solution Approach 2:
The patent implements periodic action through the dual-reset mechanism where the second electrode of the drive transistor is reset periodically at specific phases of the driving cycle. The reset control signal operates in a periodic manner, resetting the second electrode before data writing and maintaining it at a high level during light emission. This periodic resetting compensates for threshold voltage variations that cause flickering and afterimage effects.
3Adaptability or versatility
If the driving frequency is changed, then the display can adapt to different refresh rates, but frequency-cut flicker occurs at low gray scales
Solution Approach 1:
The patent applies periodic action by implementing a dual-reset mechanism that operates at specific phases of the driving cycle. The reset control signal periodically resets the second electrode of the drive transistor before data writing and maintains it at a high level during light emission. This periodic resetting compensates for threshold voltage variations that cause frequency-cut flicker, especially at low gray scales, while allowing the display to adapt to different driving frequencies.
Data Source
AI summary
In a pixel circuit, a first reset transistor is coupled between a gate of a drive transistor and an initialization signal terminal, and a gate of the first reset transistor is coupled to a reset control terminal; a compensation transistor is coupled between the gate and a first electrode of the drive transistor, and a gate of the compensation transistor is coupled to a first scan control terminal; a data writing transistor is coupled between a second electrode of the drive transistor and a data signal terminal, and a gate of the data writing transistor is coupled to a second scan control terminal; a first light emitting control transistor is coupled between the second electrode of the drive transistor and a first power supply terminal, and a gate of the first light emitting control transistor is coupled to a light emitting control terminal.