Test Case
The equivalent circuit of a pixel operated by an active matrix driving is shown in Fig.1. Data lines are connected to a data driver generating signal pulses for picture data, and scan lines to a scan driver generating scan pulses which enable the addressing drive. Vsig, Vg are applied to data lines and scan lines respectively. A thin film transistor (TFT) is three terminals of MOS transistor 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 gate and source terminal in TFT. A liquid crystal is injected into a gap between a pixel electrode and a counter backplane electrode and it forms a liquid crystal cell capacitance (Clc). Clc is a variable capacitor which changes the value according to the applied voltage between a pixel electrode and a counter backplane electrode. Here the voltage of a pixel electrode and a counter backplane electrode are Vpix and Vcom respectively. Csc is called as a storage capacitor and parallel-connected to Clc, which has a function to hold charges on a pixel electrode while TFT is switched off.
Fig. 1. Equivalent circuit of an LCD panel operated with an active matrix driving
Timing chart for each signal pulse
Fig.2 shows wave forms applying to each bus line and electrode. The period while a pixel electrode voltage (Vpix) is higher than a common electrode voltage (Vcom) is called as a plus frame (Fig.2 (a)). Meanwhile, the period while Vpix is lower than Vcom is called as minus frame” (Fig.2 (b)). The plus frame and the minus frame are switched every frame time (Tf) .
Fig.2. Timing chart for each signal pulse applied to bus lines and electrodes
When the voltage of gate terminal connecting