Patent ID: 8144278

Claim:
A liquid crystal display device comprising: a plurality of pixels; a first thin film transistor at least in one of the plurality of pixels; second thin film transistors in a source driver and a gate driver; a leveling film over the first and second thin film transistors; and optically compensated bend mode liquid crystal molecules over the leveling film, wherein the first thin film transistor comprises a first semiconductor layer, a first gate insulating film over the first semiconductor layer, and a first gate electrode over the first gate insulating film; wherein the first semiconductor layer comprises a first channel formation region, a first impurity region and a second impurity region; wherein a concentration of impurity elements in the first impurity region is lower than a concentration of impurity elements in the second impurity region; wherein the first impurity region does not overlap the first gate electrode; wherein each of the second thin film transistors comprises a second semiconductor layer, a second gate insulating film over the second semiconductor layer, and a second gate electrode over the second gate insulating film; wherein the second semiconductor layer comprises a second channel formation region, a third impurity region and a fourth impurity region; wherein a concentration of impurity elements in the third impurity region is lower than a concentration of impurity elements in the fourth impurity region; wherein the third impurity region overlaps a part of the second gate electrode; wherein the first thin film transistor, the source driver and the gate driver are formed over the same substrate; wherein the liquid crystal display device is configured to conduct voltage gray scale and time ratio gray scale in one frame period by using n bit out of m bit digital data as information for voltage gray scale, and (m−n) bit as information for time ratio gray scale, wherein m and n are positive numbers equal to or greater than 2 and satisfy m>n; wherein the one frame period is divided into a plurality of sub-frame periods; wherein a display gray scale of each of the plurality of sub-frame periods is based on the information for voltage gray scale; wherein a display gray scale of the one frame period is obtained by totaling and time- averaging the display gray scale of each of the plurality of sub-frame periods; and wherein a same initialize voltage is applied to all of the plurality of pixels before starting each of the plurality of sub-frame periods.