Brightness adjusting circuit of liquid crystal matrix panel for picture display

摘要

A drive circuit drives a liquid crystal display device of the type in which liquid crystal fills a space between an X-Y matrix substrate having a number of picture elements each including a switching element, and a common electrode plate. The drive circuit provides an optimum picture displayed to an observer in accordance with ambient conditions such as light and temperature. To this end, a DC bias voltage to determine the operating point of the liquid crystal display device is applied to the common electrode. The brightness of the displayed picture may be controlled by adjusting the DC bias voltage. The DC bias is changed in accordance with a change in an amount of ambient light or ambient temperature. Furthermore, in accordance with the fall of the ambient temperature the DC voltage applied to the common electrode is made to oscillate at a frequency to which the liquid crystal is insensitive, with respect to the bias point. At this time, the amplitude of the oscillation is made large.