# Pixel Circuit Designs for Active Matrix Displays
## 5 Conclusions  
Displays are vital for the development of a digital society. Displays are classified into LCD, OLED, and micro-LED based on their display technologies. Displays are categorised by size into small and medium-sized displays and micro-displays. Small and medium-sized displays are typically driven by glass-based TFT, while micro-displays are usually driven by silicon-based MOSFETs. Glass-based TFTs are categorised into a-Si TFT, LTPS TFT, MO TFT, and LTPO TFT based on their semiconductor materials. In combination with the TFT device structure, TFTs are further divided into traditional single-gate TFTs and newer double-gate TFTs.  
Glass-based display technology is widely used in LCDs, OLEDs, and micro-OLEDs. LCDs are voltage-driven devices with relatively low requirements for TFTs. Therefore, a-Si TFTs are mature, inexpensive, and widely used. OLEDs and micro-LEDs are current-driven devices with high requirements for TFTs. To solve problems such as uneven display caused by poor stability, both internal and external compensation circuits have been designed. In addition, circuit structures such as mirror structures, diode-connected transistors, and synchronous emission schemes are combined to achieve low frequency, low power consumption, high resolution displays, etc. The micro-LED driving method is similar to that of OLED. Micro-LEDs adopt driving methods such as a combination of PWM and PAM to solve the problem of colour deviation caused by the shifting of its central wavelength.  
Silicon-based display technology is primarily used in micro-OLEDs and micro-LEDs. As pixel size shrinks, the device gradually suffers from decreased efficiency and increased leakage current. Therefore, MOSFETs are commonly used to drive these devices. Micro-OLEDs combine MOSFET with source followers and a capacitive voltage divider to expand the data voltage regulation range of the pixel circuit to ensure the normal work of MOSFETs. Micro-LED adopts a circuit design, such as a \"t-switch\" structure, to reduce leakage current and achieve low power consumption.  
The future display market is promising, with various display technologies gradually becoming subdivided to correspond to different device requirements. For glass-based display technology, new advancements such as LTPO technology have a broad development prospect. However, the major challenge facing LTPO technology is the compatibility with LTPS and MO processes. Silicon-based display technology is constrained by the size limitations of silicon wafer. The main direction of development is to gradually shift from micro sizes to small sizes. The key challenge in this shift lies in cost control.  
Conceptualisation, D.-M.W., H.Z., C.-H.T., W.-J.W., H.N. and B.J.; methodology, D.-M.W. and H.Z.; investigation, D.-M.W., H.Z., C.-H.T., S.Z., M.X., L.W. and B.J.; writing--original draft, D.-M.W., H.Z., C.-H.T. and B.J.; writing--review and editing, D.-M.W., H.Z., C.-H.T., S.Z., H.-D.L., L.Z., Y.C., C.W., M.X., L.W. and B.J.; visualisation, H.Z. and C.-H.T.; project administration, H.Z. and C.-H.T.; funding acquisition, H.Z., M.X. and B.J. All authors have read and agreed to the published version of the manuscript.  
This research was supported in part by the Guangdong Basic and Applied Basic Research Foundation under grant 2021B1515140053; in part by the R&D project in key areas of Dongguan City under grant 20201200300102; in part by the Guangzhou Science and Technology Program under grant 2024B01J0079; and in part by the SSL Science and Technology Commissioner Program under grant 20234368-01 KCJ-G.  
No new data were created or analyzed in this study.  
The authors declare no conflicts of interest.