Active Matrix Driving and Circuit Simulation

1.1 Equivalent circuit of a pixel in LCDs The equivalent circuit of a pixel operated by active matrix driving is shown in Fig. 1. Data lines are connected to a data driver for generating the signal pulses for the picture data. Scan lines are connected to a scan driver for generating the scan pulses which enable the addressing driving. Vsig and Vg are applied to the data lines and scan lines, respectively. The thin film transistor (TFT) has three terminals of MOS transistors, and each terminal gate, drain, and source is connected to a scan line, a data line, and a pixel electrode, respectively. Cgs means the parasitic capacitance between the gate and source terminal in the TFT. Liquid crystal is injected into the gap between the pixel electrode and the counter backplane electrode, and it forms a liquid crystal cell capacitance (Clc). Clc is a variable capacitor that changes value according to the applied voltage between the pixel electrode and a counter backplane electrode. The voltage of the pixel electrode and counter backplane electrode are denoted by Vpix and Vcom, respectively. The storage capacitor is denoted Csc, and it is connected in parallel to Clc. Its function is to hold charges on a pixel electrode while the TFT is switched off.