Patent ID: 6650341
Filing Date: 2003-11-18
Classification: G09G

Abstract:
A liquid crystal drive circuit for AC-driving a liquid crystal panel, the liquid crystal drive circuit including a switched capacitor type D/A converter having a sample period and a hold period, the liquid crystal drive circuit comprising:a differential operational amplifier; a first reference voltage connected to one input terminal of said differential operational amplifier; a first capacitor group connected to the other input terminal of said differential operational amplifier for dividing second and third reference voltages; a second capacitor group connected between an output terminal and the other input terminal of said differential operational amplifier; and switch means for changing a connection condition of said first capacitor group and said second capacitor group to said differential operational amplifier, said switch means being on-off controlled at every predetermined period for changing said connection condition, a plurality of liquid crystal drive circuits provided to realize a multi-output, and wherein said differential operational amplifier has a non-inverted input terminal connected to a first reference voltage input terminal, wherein said first capacitor group is constituted of a plurality of unitary capacitors as a basic element, which are connected to an inverted input terminal of said differential operational amplifier, said second capacitor group is constituted of a plurality of unitary capacitors as a basic element, which are connected to said inverted input terminal of said differential operational amplifier, and wherein said switch means comprises a â€œ1Aâ€ th switch group having switches each having one end connected to a corresponding capacitor in said first capacitor group and the other end connected to a second reference voltage input terminal, a â€œ2Aâ€ th switch group having switches each having one end connected to a corresponding capacitor in said first capacitor group, a â€œ3Aâ€ th switch having one end connected to the other end of said â€œ2Aâ€ th switch group and the other end connected to said inverted input terminal of said differential operational amplifier, a â€œ4Aâ€ th switch having one end connected to the other end of said â€œ2Aâ€  the switch group and the one end of said â€œ3Aâ€ th switch and the other end connected to said output terminal of said differential operational amplifier, a â€œ5Aâ€ th switch having one end connected to the other end of said â€œ2Aâ€ th switch group, the one end of said â€œ3Aâ€ th switch and the one end of said â€œ4Aâ€ th switch and the other end connected to said first reference voltage input terminal and said non-inverted input terminal of said differential operational amplifier, and a â€œBAâ€ th switch having one end connected to the other end of said â€œ2Aâ€ th switch group and the respective one ends of said â€œ3Aâ€ th to â€œ5Aâ€ th switch and the other end connected to said third reference voltage input terminal, a â€œ1Bâ€ th switch group having switches each having one end connected to a corresponding capacitor in said second capacitor group and the other end connected to said second reference voltage input terminal, a â€œ2Bâ€ th switch group having switches each having one end connected to a corresponding capacitor in said second capacitor group, a â€œ3Bâ€ th switch having one end connected to the other end of said â€œ2Bâ€ th switch group and the other end connected to said inverted input terminal of said differential operational amplifier, a â€œ4Bâ€ th switch having one end connected to the other end of said â€œ2Bâ€ th switch group and said one end of said â€œ3Bâ€ the switch and the other end connected to said output terminal of said differential operational amplifier, aâ€œ5Bâ€ th switch having one end connected to the other end of said â€œ2Bâ€ th switch group, said one end of said â€œ3Bâ€ th switch and said one end of said â€œ4Bâ€ th switch and the other end connected to said first reference voltage input terminal and said non-inverted input terminal of said differential operational amplifier, and a â€œ6Bâ€ th switch having one end connected to the other end of said â€œ2Bâ€ th switch group and said respective one ends of said â€œ3Bâ€ th to â€œ5Bâ€ th switch and the other end connected to said third reference voltage input terminal.