Computer graphics processing and selective visual display system – Display driving control circuitry
Reexamination Certificate
1998-08-18
2001-11-06
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Display driving control circuitry
C345S087000, C345S095000, C345S098000, C345S100000, C345S101000, C345S212000, C327S530000
Reexamination Certificate
active
06313830
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display which is especially driven by a liquid crystal display driver.
DESCRIPTION OF THE RELATED ART
In the conventional display device, a liquid crystal display is used to make the display device smaller. For this liquid crystal display, a liquid crystal display (hereinafter referred to as LCD) panel of active matrix system using thin film transistor (hereinafter referred to as TFT) that functions as a switch for each pixel is frequently used.
In order to drive this TFT-LCD panel, an LCD driver has been used. This conventional LCD driver is explained in
FIGS. 1
,
2
and
3
.
FIG. 1
shows a block diagram of a conventional LCD driver.
The LCD driver in
FIG. 1
comprises a shift register
501
into which the clock signal CLK is inputted, a data register
503
into which red data DR, green data DG and blue data DB, as display data of red, green and blue are inputted, a latch
505
into which a strobe signal STB is inputted, a DAC
507
into which a strobe signal is inputted and an output amplifier
509
into which a strobe signal is inputted. And the output amplifier
509
comprises plural output amplifiers having respective output terminals.
The shift register
501
into which a clock signal CLK is inputted outputs the data into the data register
503
.
The data register
503
into which display data DR, DG and DB are inputted outputs the data into the latch
505
based on the output data from the shift register
501
.
The latch
505
into which a strobe signal STB and data from the data register
503
are inputted latches the data and also outputs the latched data to the DAC
507
.
The DAC
507
which a strobe signal STB is inputted into and which received the data from the latch
505
converts the data from digital to analog and outputs an analog signal to the output amplifier
509
.
The output amplifier
509
into which a strobe signal STB is inputted outputs the output signal from each output terminal based on the outputted data from the DAC
507
.
FIG. 2
shows a timing chart of the signals in the LCD driver, shown in FIG.
1
. These are a clock signal
601
, several data which are synchronized with this clock signal
601
such as red data
603
, green data
605
, blue data
607
, a strobe signal
609
and an analog output
611
.
FIG. 3
shows a block diagram of the conventional output amplifier shown in FIG.
2
. As shown in
FIG. 3
, this output amplifier comprises a constant current circuit
701
whose one terminal is grounded and the other is connected to a differential input circuit
703
, a differential input circuit
703
having a voltage by a power supply
705
supplied, inputting an analog input and a current outputted from a constant current circuit
701
, and outputting an output signal to a gate of a transistor
711
, a power supply
705
supplying voltage to all the output amplifier, a bias current circuit
707
inputting the analog input and outputting a bias current to a constant current circuit
709
, a constant current circuit
709
inputting a voltage from the power supply
705
and a bias current from the bias current circuit
707
, and outputting an output signal to a terminal of a transistor
711
, a transistor
711
whose one terminal is connected to the constant current circuit
709
, the other terminal is grounded and a gate is connected to the differential input circuit
703
, and an output terminal
713
which connects between the constant current circuit
709
and the transistor
711
.
The drive of the TFT-LCD panel is implemented by said LCD panel.
As mentioned above, the TFT-LCD panel is driven by the LCD driver, however the drive is transmitted to the TFT-LCD panel through a source line.
On the other hand, the TFT-LCD panel has some problem of line defect in the production process. Therefore, to increase the yield ratio, by setting wiring around the surroundings part of the LCD panel beforehand, the line defect is amended.
FIG. 4
shows an example of the TFT-LCD panel with line defects. In
FIG. 4
the conceptual diagram is indicated to show the process of amendment of the line defects in both the present invention and the conventional LCD.
As shown in
FIG. 4
, plural source lines are wired at the LCD panel
401
. The source lines which have line defects
403
are indicated as to be amended source lines
405
. These source lines are connected to the output terminal of the LCD driver.
At the amended source lines
405
, surrounded wiring
407
has been disposed.
As indicated in
FIG. 4
, at the line defect of the LCD, the yield ratio of the LCD has been increased by utilizing the surrounded wiring
407
.
In the source lines of the LCD, as shown in
FIG. 4
, two kinds of source lines exist, one being amended source lines and the other being non-amended source lines.
The electric characteristics of the amended source line and non-amended source line are not the same. In particular, the wiring resistance and capacitance of the amended source line are larger than those of the non-amended source line, and the output amplifier for that line needs higher output power.
Therefore, in the conventional device, to drive the amended source line, the output capacity of the LCD driver is designed to meet the load of the amended source line (heavy load). Thus, to drive the amended source line, the output power for the line defect needs to be higher. Therefore a size of a transistor within the output amplifier is changed so that the output power of the whole amplifier is increased.
However, in the LCD diver of the above mentioned conventional LCD, the current consumption of the output amplifier is determined by the inside bias current, and both the amended source line (heavy load) and non-amended source line (light load) are driven by high power output amplifier. Therefore, the inside bias current which needs only to drive the heavy load in the amended source line is applied for the whole output amplifier applying all source lines, and for the non-amended light load source line, the output power is too high, and is wasted current.
In particular, the conventional LCD panel can provide only about scores of surrounded wiring around the panel and most of the source lines are light load, which makes this problem remarkable.
Additionally, because the conventional LCD driver is designed for the output capacity to meet heavy load, in cases where the difference between light load and heavy load is too big, in the light load source line an over shoot or an under shoot of output wave form is generated, and there may be abnormal voltage for writing to a liquid crystal may happen.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a liquid crystal display which is capable of decreasing the current consumption and can prevent the abnormal writing to a liquid crystal.
According to a first aspect of the present invention, there is provided a liquid crystal display having a liquid crystal display driver that drives transistors through plural source lines on the substrate in which transistors and pixel electrodes are disposed in matrix, the liquid crystal display driver comprising: a shift register for inputting a clock signal; a data register for receiving the data from the shift register, and inputting display data of red, green and blue and an output power control signal designating amended source lines, the output power control signal accompanied with the display data of red, green and blue; a latch for receiving the data from the data register and inputting a strobe signal; a digital to analog converter for receiving the data from the latch and with the inputting of a strobe signal, converting the inputted digital data to analog data; and an output amplifier comprising plural output circuits which receives the data from the digital to analog converter and outputs to the plural source lines respectively. The output amplifier makes the output power for the amended source lines higher to implement the output.
According to the present invention, by appointing
Kovalick Vincent G.
NEC Corporation
Shalwala Bipin
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