Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-03-02
2001-01-09
Nguyen, Chanh (Department: 2775)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S095000
Reexamination Certificate
active
06172661
ABSTRACT:
PRIOR ART
A TFT liquid crystal display module has been known as one of TFT liquid crystal displays.
FIG. 39
is a block diagram showing the outline configuration of the conventional TFT liquid crystal display module.
In
FIG. 39
, a liquid crystal display panel (TFT-LCD) has 640×3×480 pixels and drain drivers
511
arranged at the top and bottom of the liquid crystal display panel (TFT-LCD). The top and bottom drain drivers
511
are alternately connected to drain lines (D) of the thin-film transistors TFT to supply a liquid crystal drive voltage to the thin-film transistors TFT.
Gate lines (G) of the thin-film transistors TFT are connected with gate drivers
506
arranged by the side of the liquid crystal display panel (TFT-LCD) that supply a voltage to the thin-film transistors TFT for one horizontal operation duration.
A display controller
501
comprising one semiconductor integrated circuit (LSI) receives display data and display control signals from the computer and, based on the received signals, drives the drain drivers
511
and the gate drivers
506
.
In this process, the display data from the computer are transferred one set in each unit time, the one set comprising red (R), green (G) and blue (B) data and forming one pixel.
The display data has either 12 bits, 4 for each color, or 18 bits, 6 for each color.
Because the drain drivers
511
are provided at the top and the bottom, there are provided two systems of both the control signal bus and the display data bus for sending drive outputs to the drain drivers
511
.
FIG. 40
is a block diagram showing the outline configuration of the drain driver
511
of the conventional TFT liquid crystal display module.
As shown in
FIG. 40
, the drain driver
511
consists of a data latch unit
551
for display data and an output voltage generation circuit
552
.
The drain driver
511
of
FIG. 40
is supplied 6-bit display data and 9-value grey-scale reference voltage and produces 64 levels of output voltage.
The data latch unit
551
takes in the same number of display data as that of output lines in synchronism with the data latch clock signal (CL
1
), and the output voltage generation circuit
552
selects an output voltage corresponding to the display data from the data latch unit
551
from among the 64 grey-scale output voltages generated from the externally supplied grey-scale reference voltage and outputs the selected voltage to the drain signal line.
FIG. 41
shows the circuit configuration of the output voltage generation circuit
552
of the drain driver
511
of the conventional liquid crystal display module. The figure represents only one of the output voltage generation circuits
552
, which are provided in number equal to that of the drain signal lines.
As shown in
FIG. 41
, the output voltage generation circuit divides each of the voltages (V
0
-V
8
) between the nine external grey-scale reference voltage values into eight equal sections (VO
0
-VO
64
), which are selected and output by a decoder
553
.
FIG. 42
shows the relation between the grey-scale reference voltages of FIG.
41
and the output voltages.
In
FIG. 42
a total of 65 output voltage values are obtained, of which V
064
equal to V
8
is not used.
FIELD OF INDUSTRIAL APPLICATION
The present invention relates to a liquid crystal display device and more particularly to a technology effectively applied to thin-film transistor (TFT) liquid crystal displays.
PROBLEM TO BE SOLVED BY THE INVENTION
It is known from U.S. Pat. No. 4,906,984 that, by adopting as a common electrode drive method for the TFT liquid crystal display module a common electrode AC drive method which converts the voltage applied to the common electrode into an AC voltage, it is possible to use a drain driver with a low withstand voltage.
The conventional common electrode AC drive method has a first drawback; that is, the use of a square wave form as an AC wave form causes a large peak current when a phase is switched, so the common electrode drive transistor needs to have a large current rating, which in turn increases the size of the drive circuit.
In the drive circuit of the TFT liquid crystal display, we can use a level shift circuit of a differential amplifier type.
In the level shift circuit of the differential amplifier type, when noise is superimposed on a positive power supply, it is also fed to the power supply output terminal. Because the noise superimposed on the positive power supply line has a different wave form than the noise transmitted to the output terminal, there is a second drawback that the buffer circuit, which is connected behind the level shift circuit and operates on the positive power supply as the reference, will malfunction.
Further, it is known from U.S. Pat. No. 5,250,937 that, by changing the voltage applied between the pixel electrode and an opposing electrode of the liquid crystal, the viewing angle can be adjusted. With the conventional TFT liquid crystal display module, the voltage applied to the drain signal line is changed to adjust the viewing angle.
Generally, in the TFT liquid crystal display module that performs the common electrode AC drive, there is a third drawback that the viewing angle adjustment by changing the voltage applied to the drain signal line (D) results in a complicated circuit configuration.
The relation between applied voltage and transmission factor of a liquid crystal is generally nonlinear as a typical example shows in FIG.
43
.
As shown in
FIG. 43
, the applied voltage-transmission factor characteristic is significantly nonlinear at the ends of the voltage range used and relatively linear at the center.
Normally, a desired linear grey-scale display can be obtained by supplying the drain driver with the voltage value that is corresponding to this nonlinearity.
With the drain driver
511
which generates the voltage values (VO
0
-VO
64
) by dividing each of the nine external grey-scale reference voltages (V
0
-V
8
) into eight equal parts and which selects and outputs one of the 64 shade level voltages, As shown in
FIG. 42
, however, there are only eight shade levels out of the 64 from which the user can arbitrarily select to set the output voltage.
The shade level voltages internally generated by the drain driver
511
are produced by equally dividing each of the external grey-scale reference voltages for the sake of versatility of the drain driver
511
and of simplification of its internal circuit.
For this reason, there is a fourth drawback that the shade level voltages internally generated by the drain driver
511
deviate from the linear voltages intended to be used to produce a desired grey-scale display.
Although the effects of the above-mentioned deviation are not so significant in the central portion of the voltage range that exhibits a relatively linear characteristic, they cannot be ignored at the ends of the voltage range where significant nonlinearity is observed and it is not possible to produce a good grey-scale display characteristic.
While this deviation may be reduced by increasing the number of external grey-scale reference voltages, this method has a problem of increasing the number of input leads of the drain driver
511
and complicating the configuration of the external circuit for driving the drain drivers
511
. This method, therefore, is not practical.
With the technique shown in
FIG. 39
, there is a fifth drawback that because the drain drivers
511
are arranged at the top and bottom of the liquid crystal display panel (TFT-LCD), the frame edge portions at the upper and lower portions of the TFT liquid crystal display module are required to be equal in lengths (areas).
The market needs, however, larger displays in smaller frames.
In the above-mentioned conventional technique, all the drain drivers
511
are driven by the clock signal from the display controller
501
alone.
In this case, when the number of drain drivers
511
becomes large, there is a sixth drawback that the buffer circuit
210
may become unable to drive the drain drivers
511
with the result that stable clo
Hasegawa Kaoru
Igarashi Youichi
Imajo Yoshihiro
Kondo Hironori
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Nguyen Chanh
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