Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
2001-02-05
2003-09-16
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S087000
Reexamination Certificate
active
06621489
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an LCD display unit capable of preventing turbulence of images, generated when the image on the LCD display is switched or the LCD power supply is turned off, and more specifically to an LCD display unit that prevents the turbulence of images in the reflex LCD.
2. Related Art
In replacement of the cathode-ray tube that has been used in various types of information display units, the Liquid Crystal Display (hereunder, referred to as “LCD”) has widely been employed, because it has advantages of requiring less space for installation and less power consumption. The LCD has various types. From the standpoint of structure, there is the direct-view type in which a user views the display itself directly, and the projection type in which a user views images projected on a screen. The widely used direct-view type LCD includes the transmission type LCD having a backlight, and the reflex type LCD utilizing the reflected light of natural light and/or a room lamp light. Since it is impossible to present visible images without a surrounding light source, the reflex type LCD includes a type provided with a backlight, so that backlighting can be used as needed.
Because the liquid crystal substance does not emit spontaneously, the transmission type LCD is provided with a backlight on the backside of an array substrate, which irradiates a light thereon. While the light permeates through the array substrate containing the liquid crystal substance and the liquid crystal cells, the liquid crystal produces a torsion effect on the light, whereby the transmission type LCD gives a viewer images obtained by the light transmitting through a polarization plate. In contrast to this, the reflex type LCD makes natural light being irradiated on the surface of the liquid crystal cell substrate reflect on the array substrate and the liquid crystal cell substrate to thereby give a viewer images.
Further, the LCD uses the Nematic liquid crystal substance as represented by the TN type, STN type, DSTN type, etc., which includes the passive matrix LCD as a simple matrix system using passive elements only, not using active elements, and the active matrix LCD inside of which the drive control is carried out by the active elements such as the thin film transistors and diodes represented by the TFT type LCD. In recent years, there have been strong demands for a fine color image with a good response on a wide display such as a personal computer display and a TV display, etc., so that the active matrix LCD has been adopted increasingly.
Such an active matrix LCD will be explained with a representative TFT type LCD as an example, with reference to FIG.
5
. Thin film transistors (hereunder, abbreviated as TFT) as the active elements are connected to the intersections of the longitudinal pixel electrodes X and the lateral pixel electrodes Y. One end of each TFT is supplied with a data signal and the other end thereof is connected to a storage capacitor (not illustrated) and the pixels formed by the liquid crystal substance are inserted in parallel with the storage capacitors. Further, the gate electrodes are connected to the lateral pixel electrodes Y, to which address signals are supplied from the outside, and in accordance with the address signals, the data signals are transmitted to the pixels through the TFTs.
The active matrix LCD of the TFT type formed on the foregoing principle is driven and controlled by a drive circuit as shown in
FIG. 6
, for example. This drive circuit is composed of, to classify broadly, a signal control circuit
32
, power supply circuit
34
, gradation voltage circuit
33
, facing electrode drive circuit
35
, address line drive circuit
36
as a gate driver, data line drive circuit
37
as a source driver, and the like, which drives a liquid crystal panel
31
having a structure as shown in FIG.
5
. The drive circuit including these control circuits forms a liquid crystal module
30
.
In such a drive circuit, as a power supply voltage, clock signals &phgr;
1
, &phgr;
2
, a synchronizing signal, and a data signal are supplied, the signal control circuit
32
supplies the data line drive circuit
37
as the source driver with the data signal, the control signal, and the clock signal &phgr;
1
, and supplies the address line drive circuit
36
as the gate driver with the control signal, clock signal &phgr;
2
. The power supply circuit
34
regulates the power supply supplied from the outside, and supplies a necessary power supply voltage to a driver IC of the data line drive circuit
37
and a driver IC of the address line drive circuit
36
. The gradation voltage circuit
33
supplies the data line drive circuit
37
with a gradation voltage used by the data driver for generating an output voltage. Further, the facing electrode drive circuit
35
supplies a common voltage to common electrodes facing the pixel electrodes.
In the TFT type LCD, a gate voltage from the address line drive circuit
36
turns the TFT on/off by row, and during the on interval of the TFT, the output voltage from the data line drive circuit
37
enters a source electrode
45
of a TFT
44
through a data line
43
. Through a drain electrode
46
, the output voltage is applied across a pixel electrode, which is illustrated by a capacitor
50
of the pixel portion represented by way of the equivalent circuit in the drawing, and a storage capacitor
51
that holds the supplied voltage, which is connected in parallel with the pixel electrode, whereby an image is displayed. Here, the difference between the potential of the pixel electrode and the potential of the facing electrode is the voltage applied to the liquid crystal layer, and this applied voltage presents a liquid crystal image with an appropriate gradation.
After the gate of the TFT is switched off thereafter, the voltage stored across the storage capacitor
51
maintains the displayed image as it is. In order to present the next frame image, the gate voltage is again supplied to the TFT to turn it on, and the reverse voltage to the former is supplied to the pixel and the storage capacitor. Thereby, the charges across the pixel and the charges across the storage capacitor are discharged, and next a specific reverse voltage for presenting an image of a specific gradation is stored across the storage capacitor
51
to present a next frame image. To repeat such operations presents a specific image on the whole display. Here, in
FIG. 6
, the storage capacitor
51
is connected to a Cs line
42
provided separately from the common electrode
41
, however it can be connected to the common electrode
41
without using the Cs line
42
.
In the LCD display unit that carries out the foregoing operations, to finish the liquid crystal display from the state of a normal liquid crystal display, all the power supply lines are brought into the off state. Consequently, the power supply line leading to the power supply circuit
34
is switched off, and the data signal line is switched off at the same time. Since the TFT is brought into the off state at that time, the storage capacitor
51
that stores a charge so as to continuously maintain a specific voltage for maintaining the image on each pixel will continue to maintain the state with the charge held. However, the charges are discharged gradually from leakage elements such as an internal resistance of the TFT
44
and the like, which causes uncertain turbulence of the liquid crystal in the pixel portions of the entire display, depending on characteristics such as the discharge characteristics of the elements and the characteristics of the elements that are influenced by the internal and external circuits. Here, in the reflex type LCD, for a period of time after turning off the power, the disturbed images can be seen through the uncertain turbulence of the liquid crystal, which presents blurry, irregular after-images.
With respect to this point, the backlight type LCD that has widely been used is provided with a backlight on the backside of t
Kondo Tsuyoshi
Yanagisawa Tetsuya
Alpine Electronics Inc.
Brinks Hofer Gilson & Lione
Eisen Alexander
Hjerpe Richard
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