Source driver of liquid crystal display
View Patent ↗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 a plurality of 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 including: 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.
1. 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.
2. The source driver as recited in claim 1 , wherein if the coarse gradation voltage generator has various resistances, the resistance R is the largest resistance among the various resistances.
3. The source driver as recited in claim 2 , wherein when one resistance of the two resistors connected to the first decoder in a resistor string of the fine gradation voltage generator is added to a turn-on resistance of all switches contained in the first decoder, the added resistance meets the equation.
4. An apparatus for converting a digital signal into an analog signal, comprising:
L DACs (digital-to-analog converters) including:
a first decoder for selecting two consecutive voltages among 2 M gradation voltages in response to M-bit digital signals (where L and M are positive integers);
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 (where N is a positive integer); 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; and
a coarse gradation voltage generator, configured with 2 M resistors connected in series, for generating the 2 M gradation voltages,
wherein 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.
5. The apparatus as recited in claim 4 , wherein if the coarse gradation voltage generator has various resistances, the resistance R is the largest resistance among the various resistances.
6. The apparatus as recited in claim 5 , wherein when one resistance of two resistors connected to the first decoder in a resistor string of the fine gradation voltage generator is added to a turn-on resistance of all switches contained in the first decoder, the added resistance meets the equation.