Abstract 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.
A brightness adjusting circuit of a liquid crystal matrix panel for picture display comprising: an X-Y matrix panel having a plurality of picture elements each connected at one terminal to a semiconductor switching element and a memory element and at another terminal to an electrode common to all the picture elements; a plurality of X electrodes and Y electrodes connected to control said semiconductor switching elements, whereby a gate signal applied to an X electrode transfers a voltage applied to said Y signal to said memory element; means for applying a video signal to said Y electrodes; means for applying a scanning gate signal to said X electrodes and for storing in said memory element the voltage corresponding to the video signal applied to said Y electrode by successively making the semiconductor switching elements conductive; means for applying a variable DC voltage to said common electrode whereby the brightness of a picture displayed may be varied; means for superimposing an AC signal with a frequency to which the liquid crystal does not respond on the variable DC voltage; means for detecting the ambient temperature of said matrix panel; and means for controlling the DC voltage applied to the common electrode in accordance with the detected temperature.
Claim 2
Dependent Claim
206 words
A brightness adjusting circuit of a liquid crystal matrix panel for picture display comprising: an X-Y matrix panel having a plurality of picture elements each connected at one terminal to a semiconductor switching element and a memory element and at another terminal to an electrode common to all the picture elements; a plurality of X electrodes and Y electrodes connected to control said semiconductor switching elements, whereby a gate signal applied to an X electrode transfers a voltage applied to said Y signal to said memory element; means for applying a video signal to said Y electrodes; means for applying a scanning gate signal to said X electrodes and for storing in said memory element the voltage corresponding to the video signal applied to said Y electrode by successively making the semiconductor switching elements conductive; means for applying a variable DC voltage to said common electrode whereby the brightness of a picture displayed may be varied; means for superimposing an AC signal with a frequency to which the liquid crystal does not respond on the variable DC voltage; means for detecting the ambient temperature of said matrix panel; and means for controlling the DC voltage applied to the common electrode in accordance with the detected temperature.
Claim 3
Dependent Claim
19 words
A brightness adjusting circuit according to claim 1, wherein said AC signal is applied during a vertical flyback period.
Claim 4
Dependent Claim
32 words
A brightness adjusting circuit according to claim 1, wherein the amplitude of said AC signal superimposed to the DC voltage applied to said common electrode is increased as the ambient temperature decreases.