2T2C Pixel Driving Circuit for Dynamic Frame Rate Adaptation
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Solution Overview
Problem
Traditional one transistor-two capacitor (1T2C) pixel driving circuits are not suitable for dynamic frame rate technology, as they fail to meet the requirements of both high-frequency and low-frequency display applications due to limitations in charging and image-holding abilities.
Innovation Solution
A two transistor-two capacitor (2T2C) pixel driving circuit is designed, utilizing a low-temperature polysilicon (LTPS) TFT and an oxide semiconductor TFT, where one transistor is normally turned on to maintain voltage and the other serves as a driving switch, alternately operating in low-frequency and high-frequency states to satisfy different requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If LTPS technology is used, then charging ability is improved, but image-holding ability deteriorates
Solution Approach 1:
The pixel driving circuit is divided into two separate transistors: T1 (LTPS TFT) dedicated to charging operations and T2 (IGZO TFT) dedicated to image-holding operations. This segmentation allows each transistor to specialize in its optimal function, with LTPS providing high-speed charging and IGZO providing low-leakage holding, thereby resolving the contradiction between charging ability and image-holding ability.
Solution Approach 2:
Different materials with distinct local properties are assigned to different functional roles within the circuit. LTPS material is used where high mobility and fast charging are needed (T1), while IGZO material is used where low leakage and stable holding are needed (T2). This local quality differentiation enables simultaneous optimization of both charging and holding performance.
2Stability of the object's composition
If IGZO technology is used, then image-holding ability is improved, but charging ability deteriorates
Solution Approach 1:
The circuit functionality is segmented such that IGZO-based T2 handles only the image-holding function while LTPS-based T1 handles the charging function. This prevents the IGZO material's limited charging speed from becoming a bottleneck, as charging is delegated to the faster LTPS transistor.
Solution Approach 2:
IGZO material is strategically placed in T2 where its low leakage current and high uniformity provide superior image-holding capability, while the charging function is localized to T1 where LTPS material's high mobility provides fast charging. Each material's local quality is optimized for its specific role.
3Ease of manufacture
If single-element backplane technology is used, then manufacturing simplicity is maintained, but adaptability to dynamic frame rate deteriorates
Solution Approach 1:
The pixel circuit achieves multi-functionality by integrating two different transistor technologies (LTPS and IGZO) that can adapt to different operating conditions. The circuit can dynamically switch between high-frequency mode (using LTPS for charging) and low-frequency mode (using IGZO for holding), making it universally applicable across diverse frame rate requirements.
Solution Approach 2:
The backplane combines two different semiconductor materials (LTPS and IGZO) in a composite transistor structure. This composite approach leverages the complementary strengths of both materials, enabling the circuit to adapt to dynamic frame rate requirements while maintaining manufacturability through established TFT fabrication processes.
4Speed
If high refresh rate is used, then display smoothness is improved, but logic power consumption increases
Solution Approach 1:
The circuit segments the operational responsibilities between T1 and T2, allowing the LTPS transistor to handle fast charging during high refresh rate periods while the IGZO transistor maintains low leakage during image holding. This segmentation enables high refresh rates to be achieved with reduced overall power consumption compared to using only LTPS transistors.
Solution Approach 2:
The circuit dynamically changes operational parameters by switching between different transistor configurations based on refresh rate requirements. During high refresh rates, LTPS provides fast charging; during lower refresh rates, IGZO provides low-leakage holding, thereby adapting power consumption to actual display needs and reducing waste.
Data Source
AI summary
In a pixel driving circuit and a display panel provided, a first transistor or a second transistor is controlled to maintain that the first transistor or the second transistor is normally turned on. The one of the transistors that is normally turned on is coupled to a common terminal. The other of the transistors serves as a driving switch that receives a row scan signal and a data signal to charge a liquid crystal capacitor and a storage capacitor. Thus, when the pixel driving circuit is in the low-frequency state or the high-frequency state, the first transistor and the second transistor can alternately operate to satisfy different operating requirements.