Patent ID: 7511692
Filing Date: 2009-03-31
Classification: G09G,H03M

Abstract:
1. A gradation voltage selecting circuit comprising: a plurality of gradation selecting MOS transistor groups, each of which corresponds to one of plurality of gradation voltages; M-pieces (M is a positive integer) half gradation voltage generating MOS transistor groups which are connected to each other in series; a switching portion; and a control portion which supplies a first control signal in response to a first display data, and supplies a second control signal in response to a second display data, wherein a first gradation selecting MOS transistor group as one of said plurality of gradation selecting MOS transistor groups selects a first gradation voltage corresponding to said first gradation selecting MOS transistor group in response to one of said first and second control signals, a second gradation selecting MOS transistor group as one of said plurality of gradation selecting MOS transistor groups selects a second gradation voltage corresponding to said second gradation selecting MOS transistor group in response to one of said first and second control signals, said first and second gradation selecting MOS transistor groups and said M-pieces half gradation voltage generating MOS transistor groups voltage-divide a gradation voltage between said first gradation voltage and said second gradation voltage into (M+2) equal parts in response to said second control signal, and generate (M+1)-pieces half gradation voltages, said switching portion outputs said first gradation voltage selected by said first gradation selecting MOS transistor group into a display portion in response to said first control signal, and selects and outputs one of said (M+1)-pieces half gradation voltage into the display portion in response to said second control signal, and said (M+1)-pieces half gradation voltages are detennined by ON resistance of said first and second gradation selecting MOS transistor groups and said half gradation voltage generating MOS transistor groups, wherein each of said M-pieces half gradation voltage generating MOS transistor groups includes N-pieces (N is a integer equal to or more than 2) MOS transistors connected to each other in series, said M-pieces half gradation voltage generating MOS transistor groups includes a control half gradation voltage generating MOS transistor group, of which J-pieces (J is a positive integer equal to or less than N) MOS transistors receives said second control signal, (N-J)-pieces MOS transistors of said control half gradation voltage generating MOS transistor group receives a third control signal for always turning on, and N-pieces MOS transistors of said M-pieces half gradation voltage generating MOS transistor groups other than said control half gradation voltage generating MOS transistor group receives said third control signal.