Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-01-28
2002-07-09
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S087000, C345S090000, C345S092000, C345S093000, C345S094000, C345S096000, C345S204000, C345S209000, C345S210000, C345S211000, C345S213000, C349S042000
Reexamination Certificate
active
06417827
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device and, more particularly, to an art useful in application to video signal line driving means of a liquid crystal display device capable of providing multilevel grayscale display.
2. Description of the Related Art
Liquid crystal display devices are widely used as display devices for OA equipment such as personal computers. The liquid crystal display devices are mainly classified into a simple matrix type in which pixels are formed at the intersections of stripe-shaped electrodes disposed to intersect with one another, and an active matrix type which has an active element such as a thin-film transistor (TFT) for each pixel and turns on and off the active element.
The active matrix type of liquid crystal display device includes a TFT liquid crystal panel, scanning signal line driving means and video signal line driving means for supplying a scanning voltage and a video signal voltage, respectively, to scanning signal lines (gate lines) and video signal lines (drain lines) all of which are disposed over this liquid crystal panel, and a display control unit as well as an internal power supply circuit for supplying various control signals and display data outputted from a host side such as a personal computer, to the scanning signal line driving means and the video signal line driving means as displaying signals.
FIG. 28
is a schematic block diagram illustrating the construction of a liquid crystal display device to which the present invention is applied. A liquid crystal panel
281
which constitutes this liquid crystal display device is a thin-film transistor type of active matrix liquid crystal display device (TFT-LCD), and a plurality of video signal line driving circuits (hereinafter referred to also as drain drivers)
282
and a plurality of scanning signal line driving circuits (hereinafter referred to also as gate drivers)
283
are arranged over the top side of the liquid crystal panel
281
.
The liquid crystal panel
281
is made of, for example, 1024×768 picture elements (pixels: Pix) each of which is formed by three color pixels of red (R), green (G) and blue (B).
A control signal, which is made of three color display data (video signals) for red (R), green (G) and blue (B), a clock signal, a display timing signal and a synchronizing signal all of which are outputted from the host side such as a personal computer, is inputted to a display control device
285
via an interface connector
284
.
The display control device
285
generates display data of a form displayable on the liquid crystal panel on the basis of the control signal, and supplies the display data to the drain drivers
282
via a data bus. At the same time, the display control device
285
supplies timing signals, (a carry input, CLK
1
, CLK
2
) such as a display start timing clock, a line clock and a pixel clock to the drain drivers
282
.
An internal power supply circuit
286
generates a reference voltage (V
9
to V
0
) for producing a display grayscale and supplies the reference voltage to the drain drivers
282
, and also applies a scanning voltage (a gate voltage) to the gate drivers
283
.
Each of the drain drivers
282
is assigned to a predetermined number of video signal lines (drain lines), and is arranged to serially give a carry output to the next drain driver after a predetermined number of counts.
Each of the drain drivers
282
is provided with a grayscale generation circuit for generating a grayscale voltage corresponding to display data for the drain lines and an amplifying circuit for amplifying the generated grayscale voltage and outputting a video signal voltage corresponding to the display data to each of the drain lines.
In addition, in the TFT type of liquid crystal display device, to prevent burn-in on a liquid crystal layer, the grayscale voltage to be applied to the drain lines needs to be inverted in polarity with respect to a counter electrode (hereinafter, VCOM) for each frame. As methods of realizing this, there are VCOM alternating current driving which varies the polarity of the counter electrode as well, and dot inversion driving which varies the drain lines to a great extent with the counter electrode being retained in a fixed potential.
This kind of driving of a liquid crystal display device is disclosed in, for example, Japanese Patent Laid-Open No. 281930/1997.
SUMMARY OF THE INVENTION.
In recent years, the trend in TFT types of active matrix liquid crystal display devices has been toward larger screen sizes in liquid crystal panels (TFT-LCD), higher resolution, higher image quality and lower power consumption. In addition, in order to omit a useless space and improve the appearance of a display device, it has been demanded that the size of its frame portion be made as small as possible.
In other words, as the market becomes more mature, it is becoming more indispensable to lower the prices of liquid crystal display devices, and further reductions in the mounting areas of drain drivers as well as reductions in the sizes of frame portions are demanded. In addition, as notebook personal computers become more widely used, the necessity for long-time driving using batteries increases and lower power consumption in liquid crystal display devices is demanded.
As described above, a grayscale voltage to be applied to a drain line needs to be inverted in polarity with respect to the voltage VCOM of a counter electrode for each frame. However, while the gate voltage of a TFT is changing from its on state to its off state, the gate-fo-source capacitance (Cgs) of the TFT assumes a depletion state, so that the voltage applied to the liquid crystal, i.e., the output voltage of a drain driver penetrates into this depletion portion.
Therefore, for example if the TFT is of an n type, the voltage at the gate electrode is lower during the off state than during the on state, so that since a positive voltage penetrates into a drain side, an effective voltage to be applied to the liquid crystal is lower than the output of the drain driver. Accordingly, in view of this penetration, in the n-type of TFT, it is necessary that during the application of a negative side (a low voltage side) relative to VCOM, the output voltage of the drain driver be made higher than the voltage required in the absence of the penetration.
For the above-described reason, to equalize the effective voltages of negative and positive sides relative to VCOM, it is necessary to adopt asymmetric driving in which the output voltage of the drain driver is asymmetric with respect to VCOM between the negative side (low voltage side) and the positive side (high voltage side).
In a dot inversion driver, a reductions in chip size is needed by disposing low-voltage-dedicated circuits and high-voltage-dedicated circuits, respectively, by numbers each equal to not the total number of output terminals but ½ of the same, by taking advantage of the fact that a negative side (a to voltage side) and a positive side (a high voltage side) are alternately outputted from adjacent output terminals.
Since the construction of the low-voltage-dedicated circuits and the high-voltage-dedicated circuits (a decoder construction) aims at reducing chip size, it is necessary that the switching elements of grayscale voltage selection circuits, amplifier circuits and output selection circuits be formed of only NMOSs for the low-voltage-dedicated circuits as well as of only PMOSs for the high-voltage-dedicated circuits so that the number of elements can be reduced.
FIGS. 29
to
32
are circuit diagram illustrating specific examples of the constructions of a low-voltage-dedicated circuit and a high-voltage-dedicated circuit of a drain driver.
FIGS. 29 and 30
show the low-voltage-dedicated circuit, while
FIGS. 31 and 32
show the high-voltage-dedicated circuit. Incidentally, each pair of
FIGS. 29 and 30
and
FIGS. 31 and 32
show the corresponding circuit in the form of two divided sections, because both circuits have fin
Agata Kentaro
Fujioka Takahiro
Goto Mitsuru
Nagao Shoji
Nakayasu Yozo
Hjerpe Richard
Lesperance Jean
LandOfFree
Liquid crystal display device having a wide dynamic range... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Liquid crystal display device having a wide dynamic range..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid crystal display device having a wide dynamic range... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2823259