CMOS drive system for liquid crystal display units

Claim 1

In a drive system for driving a liquid crystal unit including a common electrode, a plurality of segment electrodes, the combinations of which define display patterns, as well as liquid crystal composition between said common and said segment electrodes having a given threshold voltage value which initiates a change in the optical characteristics of said liquid crystal unit, said drive system being adapted to apply an alternating voltage higher than the threshold value to the liquid crystal unit when it is desired to be on, and to apply an alternating voltage higher than a reference potential but lower than the threshold value to the same when it is desired to be off, an improvement comprising; means for establishing first, second and third potential levels other than the reference potential, the potential difference between the third level and the reference level being selected higher than the threshold value and the potential differences of the first and second potential levels with respect to the reference level being lower than the threshold value; means for applying to the common electrode an alternating voltage alternating between the reference level and the third level and for applying to the segment electrodes an alternating voltage which alternates between the reference level and the third level in a phase opposite to the alternating polarity voltage applied to the common electrode, when the liquid crystal unit is desired to be on; and means for applying to at least one of the common electrode and the segment electrodes an alternating voltage which alternates between the first level and the second level, when the liquid crystal unit is desired to be off.