a method for driving a liquid crystal display unit is arranged to apply positive - polarity signals to drains of thin film transistors of active matrix liquid crystal elements during an interval of a 1 / n field and to apply negative - polarity signals to the drains during an interval of a next 1 / n field . this method does not need to invert a common electrode voltage v com and a signal voltage v d at each scan period . this contributes to easier design of a voltage - alternating circuit for v d or v com and reduces flicker resulting from the inversed voltage on an overall screen .