Computer graphics processing and selective visual display system – Display driving control circuitry
Reexamination Certificate
2000-08-16
2003-05-06
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Display driving control circuitry
C345S100000
Reexamination Certificate
active
06559836
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a source driver for providing signals to source lines of a liquid crystal panel, and to a method for leveling out variations in source driver outputs.
2. Description of Related Art
FIG. 10
illustrates a configuration of a source driver
72
and an example of its connection with a liquid crystal panel
70
. Liquid crystal cells are arranged in a grid pattern in the liquid crystal panel
70
. Each liquid crystal cell includes a liquid crystal and a transistor for applying to the liquid crystal cell a voltage corresponding to colors to be displayed.
As shown in
FIG. 10
, the gate terminals of the transistors of liquid crystal cells arranged in a horizontal line are connected to a gate line
78
arranged in a horizontal direction; and the source terminals of the transistors of liquid crystal cells arranged in a vertical line are connected to a source line
74
arranged in a vertical direction. The gate lines
78
are connected to a gate driver
76
which provides signals sequentially to the gate lines
78
. The source lines
74
are connected to a source driver
72
which provides signals to the source lines
74
. When a signal is provided from the gate driver
76
to a gate line
78
, the transistors (liquid crystal cells) connected to the gate line to which signal is provided are selected. When signals are provided from the source driver
72
to the source lines
74
in this state, the selected transistors (liquid crystal cells) are driven at voltages corresponding to the provided signals.
A configuration of the source driver
72
will be briefly described hereafter. The source driver
72
comprises a shift register
86
, buffers A
84
, buffers B
85
, D/A converters (digital-to-analog converters)
82
, and output amplifiers
80
. Each source line
74
is provided with a buffer A
84
, a buffer B
85
, a D/A converter
82
, and an output amplifier
80
. The buffers A
84
each store gray scale data of the pixels of one horizontal line constituting an image to be displayed on the liquid crystal panel
70
. The gray scale data are sequentially stored in the buffers A
84
in accordance with a CLOCK signal with the use of the shift register
86
. The gray scale data stored in the buffers A
84
is sent to the buffers B
85
with the use of a LOAD signal. The D/A converter
82
converts the gray scale data (digital signals) of the buffers B
85
into analog signals. The analog signals of the D/A converters
82
are amplified by the output amplifiers
80
to be output to the source lines
74
.
FIG. 11
shows an example of a portion including adjacent four output amplifiers in the source driver
72
for the liquid crystal panel shown in FIG.
10
. Analog outputs from the D/A converters
82
are input into the four output amplifiers AmpA, AmpB, AmpC, and AmpD through wirings DALA, DALB, DALC, and DALD, respectively. The outputs from the D/A converters
82
are amplified respectively by the four output amplifiers AmpA, AmpB, AmpC, and AmpD, respectively, and output to the source lines SLA, SLB, SLC, and SLD, respectively.
If all the gray scale data sent from the buffers B
85
to the D/A converters
82
are at a uniform level, all the analog voltages converted in the converter
82
are also at a uniform level. Therefore, uniform-level voltages are considered to be provided to all the source lines
74
. However, voltage levels may vary depending on offset voltage properties, gain properties, and the like in each output amplifier
80
. For this reason, even if the gray scale data of all the pixels are at a uniform level, different voltages are provided to source lines
74
. Such voltage level differences causes gray level differences, which may often appear to us to be vertical-streak noise on the liquid crystal panel.
In order to eliminate vertical streak noise, a method of sorting out a source driver having small variations in the characteristics of the output amplifiers may be employed. If the variation in the characteristics of the output amplifiers is small and all the gray scale data are at a uniform level, substantially uniform voltages can be provided to all the source lines
74
.
However, the sorting of a source driver having small variations in the characteristics of the output amplifiers leads to the reduction of yields and the increase in costs.
SUMMARY OF THE INVENTION
An object of the present invention is to level out variations in output voltage levels caused by the difference in the characteristics of the output amplifiers of a source driver, and to reduce vertical streak noise on the display screen.
A source driver for a liquid crystal panel according to the present invention comprises output amplifier switching means for switching an output amplifier, which amplifies analog signal and provides it to source lines of a liquid crystal panel, to another output amplifier at regular time intervals. Such a source driver can level out the output variations caused by the difference between individual output amplifiers, by switching among the output amplifiers, which amplify the signal and provide it to the source lines, at regular time intervals.
A method for leveling out output variations in a source driver for a liquid crystal panel according to the present invention comprises an output amplifier switching step for switching an output amplifier, which amplifies analog signal and provides it to source lines of a liquid crystal panel, to another output amplifier at regular time intervals.
REFERENCES:
patent: 4710766 (1987-12-01), Dubois et al.
patent: 4845382 (1989-07-01), Eouzan et al.
patent: 6008801 (1999-12-01), Jeong
patent: 6014122 (2000-01-01), Hashimoto
patent: 6081112 (2000-06-01), Carobolante et al.
patent: 6208094 (2001-03-01), Morrish
F. Chau & Associates LLP
Kumar Srilakshmi
Saras Steven
Trepp Robert M.
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