Patent ID: 8026890

Claim:
A flat display device which makes drive voltage polarity of pixels of adjacent lines reversed polarity, while drives to reverse drive voltage polarity of a same line on a frame-by-frame basis, wherein the flat display device comprises common voltage generation means for supplying a common voltage signal to a facing electrode of the flat display device and means for generating a common voltage control signal supplied to the common voltage generation means, characterized in that the means for generating a common voltage control signal comprises: means for generating, based on a horizontal synchronization timing signal fh, a first signal having frequency of fh/2 which reverses lines on a line-by-line basis; means for generating, based on a vertical synchronization timing signal fv, a second signal having frequency of fv/2 which reverses frames on a frame-by-frame basis; means for generating, based on the horizontal synchronization timing signal and a clock signal, a third signal of positive polarity and a third signal of negative polarity having frequency of nth of fh; multiplication means for performing multiplication of the first and second signals and outputting a fourth signal; selection means to which the third signal having positive polarity, the third signal having negative polarity, and the fourth signal are supplied, for selecting and outputting one of said third signal having positive polarity, third signal having negative polarity and said fourth signal; selection control means for determining signal selection mode according to whether one cycle of the second signal contains odd cycles of the first signals or even cycles of the first signals; and common voltage output means for generating, based on the outputted signal obtained from the selection means, the common voltage signal.