INVERSION VIDEO SIGNAL FORMING CIRCUIT, VIDEO SIGNAL AC CONVERTING CIRCUIT PROVIDED WITH ITS CIRCUIT, AND LIQUID CRYSTAL DISPLAY DEVICE PROVIDED WITH VIDEO SIGNAL AC CONVERTING CIRCUIT CONCERNED

摘要

PURPOSE:To obtain a negative polarity video signal from a collector of a third Tr by fetching a positive polarity video signal from an emitter of a first transistor (Tr) in which a video signal is inputted to a base, and forming a current mirror circuit with a second and a third Trs. CONSTITUTION:A video signal Vsig is inputted to an input terminal 1, positive and negative side power supply potentials V+, V- are set as the highest potential of V+ Vsig, and the lowest potential -2VBE of V-Vsig, and VBE denotes the base-emitter voltage of a transistor (VR). The emitter potential of a Tr 2 becomes Vsig -VBE and becomes a non-inversion video signal. As for Trs 4, 5, the base and the emitter are common, therefore, collector currents IC4, IC5 become equal, and when values of resistance 3, 6 are equalized, an inversion video signal whose amplitude is roughly equal to that of the non-inersion video signal is obtained in the collector of a Tr 5, and by switching it by a switch 8, an image signal VD which converts the signal Vsig to AC is obtained. In such a manner, a video signal can be converted to AC without using a level shifting circuit, and a liquid crystal panel can be driven.