Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2002-02-08
2004-06-08
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S098000
Reexamination Certificate
active
06747623
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device and a method of driving the same. The present invention relates particularly to an active matrix type display device having a thin film transistor (referred to as a TFT hereinafter) formed on an insulator, and a method of driving the same, more particularly to an active matrix type display device using digital signals as picture signals, and a method of driving the same.
2. Related Art
In recent years, display devices having elements formed using a semiconductor thin film on an insulator, particularly on a glass substrate, have been spreading. For example, active matrix type display devices using a TFT have been spreading. In an active matrix display device, pixels are arranged in a matrix form and TFTs are arranged onto the respective pixels (the TFTs being referred to as pixel TFTs hereinafter). The pixel TFTs are used to control the brightness of the respective pixels, thereby displaying images.
Recently, there has been developing a technique of using a polycrystal semiconductor to form not only pixel TFTs constituting pixels but also TFTs constituting a driving circuit at the same time. This technique contributes greatly to miniaturization and low power consumption of display devices. Following this, an active matrix type display device has been becoming essential for the display section of portable information-processing equipment, the applicable field of which has been markedly expanding in recent years, or the like section. Examples of the active matrix type display device include an active matrix liquid crystal display device using a liquid crystal element, and an active matrix type organic light emitting diode (OLED) display device using an OLED element. In the present specification, attention is paid mainly to the active matrix type liquid crystal display device.
The above-mentioned liquid crystal element is composed of two electrodes, oriented films formed on the respective electrodes, and a liquid crystal material sandwiched between faces of the two electrodes on which the respective oriented films are formed. As the liquid crystal material, any material having a known structure can be used.
FIG. 6
schematically illustrates a conventional active matrix type liquid crystal display device of a system in which digital picture signals are used to perform display (referred to as a digital system here in after). At the center thereof, a pixel section
1308
is arranged.
In the pixel section
1308
, plural pixels are arranged in a matrix form. Plural source signal lines and plural gate signal lines for inputting signals into the respective pixels are arranged.
A source signal line driving circuit
1301
for controlling signals to be inputted into the source signal lines is arranged over the pixel section
1308
.
The source signal line driving circuit
1301
has a shift register
1303
, the first latch circuit
1304
, the second latch circuit
1305
, D/A (digital/analogue) converter circuit
1306
, which is illustrated as DAC in
FIG. 6
, an analogue switch
1307
, and so on. Gate signal line driving circuits
1302
for controlling signals to be inputted to gate signal lines are arranged at the right and left sides of the pixel section
1308
. Only one gate signal line driving circuit
1302
may be arranged at one side of the pixel section
1308
. However, the case in which the gate signal line driving circuits are arranged at both the sides of the pixel section
1308
is more preferred from the viewpoints of driving efficiency and driving reliability.
The source signal line driving circuit
1301
has a configuration as illustrated in FIG.
7
. The source signal line driving circuit, the example of which is illustrated in
FIG. 7
, is a source signal line driving circuit corresponding to a display device which has pixels, the number of which is x in the horizontal direction, so as to display gradation by the input of 3-bit digital picture signals (the gradation being referred to as 3-bit digital gradation).
The source signal line driving circuit illustrated in
FIG. 7
has a shift register circuit (SR)
1401
, the first latch circuit (LAT
1
)
1402
, the second latch circuit (LAT
2
)
1403
, D/A converter circuit (DAC)
1404
, and so on. In
FIG. 7
, the analogue switch
1307
illustrated in
FIG. 6
is not illustrated. If necessary, a buffer circuit, a level shift circuit, and so on, which are not illustrated in
FIG. 7
, may be arranged.
Referring to
FIGS. 6 and 7
, the following will describe the operation of the display device. First, clock signals (clock pulses, inverting clock pulses) and a start pulse are inputted to the shift register
1303
, which are represented by “SR” in FIG.
7
. As a result, pulses are successively inputted from the shift register circuit
1303
to the first latch circuit
1304
, which are represented by “LAT1” in
FIG. 7
, so as to hold digital picture signals (digital data) which are similarly inputted to the first latch circuit
1304
.
The most significant bit (MSB) of the digital picture signals is represented by D
3
, and the least significant bit (LSB) of the digital picture signals is represented by D
1
. After the holding of the digital data corresponding to one horizontal term is completed in the first latch circuit
1304
, during a retrace line period the digital picture signals held in the first latch circuit
1304
are simultaneously transferred to the second latch circuit
1305
, which is represented by “LAT2” in
FIG. 7
, by the input of a latch signal (latch pulse).
Thereafter, the shift register circuit
1303
is again operated to start the holding of digital data corresponding to the next horizontal term. At the same time, the digital data held in the second latch circuit
1305
are converted to analogue signals in the D/A converter circuit
1306
, which is represented by “DAC” in FIG.
7
. The analogue signals are inputted to the source signal lines, represented by “S1” to “Sx” in
FIG. 7
, and written in the respective pixels.
FIG. 8
illustrates a configuration of the pixel section of an ordinary active matrix type liquid crystal display device.
In each of pixels, a condenser
1001
, a switching TFT
1002
, and a liquid crystal element
1003
are arranged. The gate electrode of the switching TFT
1002
in each of the pixels is connected to some line of the gate signal lines G
1
to Gy. One of the source region and the drain region of the switching TFT
1002
in each of the pixels is connected to some line of the source signal lines S
1
to Sx, and the other is connected to either electrode of the condenser
1001
and either electrode of the liquid crystal element
1003
.
The analogue signals inputted to the source signal lines S
1
to Sx are inputted to the condensers
1001
and the liquid crystal elements
1003
across the drain and the source of the switching TFTs
1002
which have become conductive by the signals inputted to the gate signal lines G
1
to Gy. Depending on the voltages of the signals, the transmittivity of the liquid crystal elements
1003
varies so that the brightness of the respective pixels is represented.
When an electric field along a given direction is constantly applied between the two electrodes of the liquid crystal element, ions in the liquid crystal material are prejudiced, thereby resulting in a problem that the liquid crystal element deteriorates. Thus, in display devices or the like wherein the ordinary liquid crystal element is used, there is used a driving method of changing, at regular intervals, the polarity of the voltage applied to the liquid crystal element so as to change the direction of the electric field applied to the two electrodes of the liquid crystal element.
For example, the following driving methods are known: a driving method called gate line inversion, a driving method called source line inversion, and a driving method called frame inversion.
In the driving method called gate line inversion, the polarities of signal voltages applied to liquid crystal elements are ma
Patel Nitin
Semiconductor Energy Laboratory Co,. Ltd.
Shalwala Bipin
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