Patent ID: 7154466

Claim:
A portable information terminal having a display device, the display device comprising: a source signal line drive circuit unit constituted by plural thin-film transistors; a gate signal line drive circuit unit constituted by plural thin-film transistors; and a pixel unit in which plural pixel thin-film transistors are arranged in a matrix shape, wherein the gate signal line drive circuit unit has at least one tristate buffer and one gate selection pulse change-over switch per a gate signal line; wherein the tristate buffer comprises a first circuit including a pair of n-channel thin-film transistor and p-channel thin-film transistor; and a second circuit including a pair of n-channel thin-film transistor and p-channel thin-film transistor, wherein the source region of the n-channel thin-film transistor in the first circuit is electrically connected, at a first connection point, to the source region of the p-channel thin-film transistor of the second circuit, wherein a first power source is electrically connected to the source region of the p-channel thin-film transistor of the first circuit, wherein a second power source having a potential lower than that of the first power source is electrically connected to the first connection point, wherein a third power source having a potential lower than the second power source is electrically connected to the source region of the n-channel thin-film transistor of the second circuit, and wherein an output signal line of the first circuit and an output signal line of the second circuit are both electrically connected to the gate signal line at a second connection point.