Recently the technology of TFT-LCD has been developed so rapidly that 5 inch diagonal size which has been used in the pocket TV is increased to be 10 inch being used currently in computer displays and TV screens.
As the display size area becomes larger, and the resolution higher, in order to maintain the high image quality, we have to consider the degradation effects due to the incorporation of the TFT-LCD parameters such as the data-line resistance, the common electrode resistance, the data-line to common parasitic capacitance, and the output current of driver ICs.
One of the degradation effects is crosstalk resulting from the coupling between the source bus-line and common electrodes. Since a source signal which represents a large number of display data is supposed to vary frequently, the common signal level is affected through the coupling effect, resulting in the degradation of pixel drive signals.
Therefore, this thesis proposes a method to compensate for this source-common electrode coupling effect by designing and experimenting a crosstalk compensation circuit. The compensation circuit consists of the parts of detection, level shift, integration, and control. The detection part detects the distorted common electrode signal caused by the coupling effect by using differential amplifiers. The level shifting is needed to adjust the detected signal to a compensation voltage level. The integration part is a switch controlled RC integrator whose output is proportional to the amount of common electrode voltage distortion.
A newly designed compensation circuit is attached to the 9.5 inch line inversion type TFT-LCD, and the performance of the compensation circuit is investigated by measuring the wave forms of source and common electrode signals. We saw that the newly designed compensation circuit greatly reduced the crosstalk between the course and the common electrode.
In this thesis, we also conclude that the line inversion type TFT-LCD, whose usage has been limited due to the crosstalk degradation despite of its cost merit can be used in large screen LCDs by incorporating a new compensation circuit. In addition, we can suppose that by incorporating a new compensation circuit, it is possible to reduce the output swing of driver ICs, resulting in the smaller chip size driver and the lower power dissipation.
