Patent ID: 7425941

Claim:
A TFT-LCD source driver for driving L channels of a liquid crystal panel (where L is a positive integer), the TFT-LCD source driver comprising L DACs (digital-to-analog converters) for converting (M+N)-bit different digital signals into analog signals (where M and N are positive integers), the DAC comprising: a coarse gradation voltage generator, configured with 2 M resistors connected in series, for generating 2 M gradation voltages; a first decoder for selecting two consecutive voltages among the 2 M gradation voltages in response to M-bit digital signals; a fine gradation voltage generator, configured with 2 N resistors connected in series, for receiving output voltages of the first decoder and outputting 2 N gradation voltages; and a second decoder for selecting one of the 2 N gradation voltages in response to the N-bit digital signals and outputting the selected gradation voltage as the analog signal, wherein the L DACs share the coarse gradation voltage generator, the first decoder and the fine gradation voltage generator are connected together without a unity gain amp, and a resistance (R ch ) of the fine gradation voltage generator meets an equation R ch ≥ ( 2 M - 1 ) · L · R 2 M · 2 N , where R is a resistance of the coarse gradation voltage generator.