# Pixel Circuit Designs for Active Matrix Displays
## 2 TFT-LCD Pixel Circuits
### TFT-LCD Novel Pixel Circuits  
1. LTPS TFT LCD pixel circuits  
The mobility of LTPS TFTs is two orders of magnitude higher than that of a-Si TFTs. LTPS TFT is usually applied to small and medium-sized LCDs with great performance. Of all the electronic modules in an LCD, the data driver is second only to the backlight in power consumption [57], with most of the power used to convert signals from digital-to-analogue. To reduce the power consumption in this part, some researchers envisioned that the pixel circuit would take on more of the driving function. [PERSON]'s team proposed a novel digital drive pixel circuit [57], which can integrate the function of a digital-to-analogue converter into a pixel. Consequently, a traditional data driver's signal conversion component can be removed, significantly lowering power usage. According to Figure 5a, the proposed pixel circuit utilises LTPS TFTs with small SS as a dynamically switched driver pixel circuit, which contains two series-connected TFIs (T2 and T3) and a resistor to form a discharge route for the pixel voltage. The pulse width of the data source controls T1 for resetting the pixel voltage and when the scanning voltage enables the pixel. The \(V_{\text{PRE}}\) is a direct current source that can be used as a common voltage for both the storage capacitor and the preset voltage. Compared with the conventional 1T1C pixel circuit, the pixel circuit is suitable for high-definition displays despite the smaller aperture. Figure 4: LCD TFT array. [PERSON], [PERSON] et al. of China Star Optoelectronics Technology (CSOT) utilised the dynamic frame rate driving method to design a pixel circuit (Figure 5c) with a boost function [58], which can achieve a 5-120 Hz wide frame rate display. The circuit can increase the current flowing through the driver TFTs by boosting the \(V\)gs of the TFTs in the active area to improve the charging performance without increasing the supply voltage. Compared to conventional IT1C circuits, this circuit increases the number of external signal lines and TFTs, resulting in a decrease in the panel's aperture ratio. To improve the applicability of this technique, the precharged TFT (T2) and the pull-down TFT (T1) in this row share settings on both sides of each row. Sharing the TFTs makes it possible to easily connect the signals of TPSW (TP switch is the switching signal needed to achieve the in-unit touch panel) and GAS1 (GAS1 is the control signal needed to achieve all gates), which avoids routing the wires in pixel areas. The charge ratio of the 120 Hz optimal circuit panel was improved by 6% compared to the normal design. Meanwhile, BOE's self-developed 4 KReal240 Hz technology effectively reduces motion trailing and improves dynamic clarity through two-frame over driving technology and optimises the charging process of the LCD unit with multi-level clock technology to significantly improve charging efficiency, further solving the display challenges at high refresh rates [62]. The above innovative circuit designs or driving techniques, such as dynamic frame rate driving, overdrive technology, and multi-stage clocking technology, are commonly used in displays with high refresh rates, low power consumption, and smooth displays to address the issues of power consumption and charging efficiency. However, increased circuit complexity brings challenges such as reduced opening rates or complex wiring. MO TFT LCD pixel circuits  
Blue phase liquid crystal display (BPLCD) applications have two key problems, namely high operating voltage and frequency effects. For BPLCD to achieve better applications, [PERSON] et al. suggested an IGZO TFT pixel circuit with an inverter topology [59]. The circuit  
Figure 5: Digital drive pixel circuit **(a)**[57], 3T1C pixel circuit with VGS boost function **(b)**[58], BPLCD pixel circuit **(c)**[59], multilevel MIP circuit **(d)**[60], MIP circuit **(e)**[61]. (Figure 5d) consists of five TFTs and two capacitors, where T2 and T3, and T4 and T5 form two sets of inverter circuits.