1. Field of the Invention
This invention relates to a driving method and device for generating activating signals that serve to activate scan lines of a display panel.
2. Description of the Related Art
Liquid crystal displays (LCD) are well known in the art and have largely replaced cathode-ray tubes (CRT) in view of their thin profile and lightweight characteristics. The LCD may be of the twisted nematic (TN) type, the super-twisted nematic (STN) type, or the thin film transistor (TFT) type. The TFT type LCD is relatively expensive to manufacture when compared to the TN and STN type LCD. Therefore, the TN and STN type LCD are often used for mobile phones and digital cameras. FIG. 1 illustrates a conventional STN type LCD that includes a display panel 92 and a driving device 91. The display panel 92 has a plurality of scan lines (Com1 to ComN). The driving device 91 is connected to the scan lines (Cora1 to ComN) of the display panel 92, and is 2 operable so as to generate activating signals that serve to activate the scan lines (Com1 to ComN) of the display panel 92 in a progressive scanning manner.
The aforementioned conventional STN type LCD is disadvantageous in that, with further reference to FIG. 2, the driving device 91 thereof generates the activating signals such that a time point at which a pulse duration of a preceding one of the activating signals, e.g., the activating signal (Si), in a consecutive pair of the activating signals ends and a time point at which a pulse duration of a succeeding one of the activating signals, i.e., the activating signal (S2), in the consecutive pair starts occur simultaneously, e.g., at a time point (t32). However, due to non-ideal effects, e.g., uneven loading effects, of the scan lines (Com1 to ComN), the activating signals (S1, S2) are attenuated, and as a consequence, the time point (t33) at which the pulse duration of the activating signal (S1′) ends may occur after the time point (t32) at which the pulse duration of the activating signal (S2′) starts. That is, the activating signal (S2′)begins to activate one of the scan lines (Com1 to ComN), e. g. , the scan line (Com2), in an adjacent pair of the scan lines (Com1 to ComN) before the activating signal (S1′) has completely deactivated the other of the scan lines (Com1 to ComN), e.g., the scan line (Com1), in the adjacent pair. This easily arises in crosstalk between he scan lines (Com1, Com2) and results in a “shadow” appearing on the display panel 92 of the conventional STN type LCD.
Furthermore, since the scan lines (Com1 to ComN) have different lengths and therefore different non-ideal effects, the scan lines (Com1 to ComN) attenuate the activating signals at different degrees. In particular, the scan line (Com1), which has the shortest length, attenuates the activating signal (Si) the least, whereas the scan line (ComN), which has the longest length, attenuates the activating signal (Sn) the most.
To solve the above-mentioned problems, it has been proposed to gradually increase the widths of the scan lines (Com1 to ComN) from the shortest scan line (Cora1) to the longest scan line (ComN). This approach, however, results in a larger area, e.g., of a circuit board (not shown), occupied by the scan lines (Com1 to ComN). Such problem becomes even more serious for display panels having a large number of scan lines. In addition, since the degree at which the width of the scan line (Corn] to ComN) is increased is determined based on a particular type of the display panel 92, once the scan lines (Com1 to ComN) are formed, e.g., on the circuit board, the widths thereof are not capable of being altered to suit a different type of display panel.