Abstract: In an active back-plane coordinate addressed liquid crystal cell whose pixels are set into one state by the application of a unidirectional potential across the thickness of the liquid crystal layer, and into the opposite state if the direction of the applied potential is reversed, refreshing is carried out in two sequential stages in order to avoid cumulative charge imbalance effects. In one stage the pixels are set to their required states, whereas in the other stage they are set to the inverse of those states.

Abstract: A co-ordinate addressed bistable liquid crystal cell is switchable between its two stable states by oppositely directed electric potential differences applied across the liquid crystal layer thickness between a front-plane electrode and the members of a co-ordinate address array of electrode pads of an active back-plane. Refresh data is compared with currently displayed data so that only those pixels scheduled for switching are subjected to switching stimuli. The electrode pad of a pixel scheduled for switching is taken from the potential of the front-plane electrode to a different potential by connection to a voltage source. It is then electrically isolated from that voltage source for a further period before its potential is restored to that of the front-plane electrode. This enables rows of pixels to be addressed with a line address time considerably shorter than the time necessary to effect full switching.