Compensative driving method for common-electrode voltage distortions in TFT-LCDs

The results of the investigation and analysis of common-electrode (counter-electrode) voltage distortions in TFT-LCDs are described. The distortions are mainly caused by voltage changes in signal bus-lines and lead to horizontal crosstalk and degradation of the contrast ratio. A new driving method, in which an ac voltage is applied independently to the storage-capacitor bus-lines, is proposed to compensate for the distortions. The effect has been confirmed by comparing it with a conventional driving method by waveform observation, horizontal-crosstalk observation, and signal-voltage-light-transmission characteristics in both common-dc and common-ac drives. It has been further confirmed that the new method can compensate for another distortion of voltages across the liquid-crystal layer, which does not occur for the common-dc drive.