Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
2001-09-26
2004-03-02
Mengistu, Amare (Department: 2673)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S214000
Reexamination Certificate
active
06700571
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device for displaying an image by using a display panel of the matrix type, with picture elements disposed in an array of matrix intersections, such as a matrix-type liquid-crystal panel or a matrix-type electroluminescent display panel; more particularly, it relates to a matrix-type display device for use in mobile information-terminal equipment, such as a mobile telephone set, that displays moving images.
2. Description of Related Art
Display devices employing matrix-type liquid crystals and the like have hitherto been used in portable information-processing equipment such as mobile telephone sets and mobile information-terminal equipment.
A basic requirement of recent mobile telephones, for example, is a battery-driven operating time of several hundred hours in the state in which a so-called standby screen is displayed. In the matrix-type display devices used in mobile telephones, therefore, a frame memory, separate from the graphics memory that has the role of input buffering of image data, is often built into the circuit for driving the liquid-crystal display panel, to reduce power consumption by making image data transfer unnecessary when a still image is displayed. That is, when a still image is displayed, these devices do not consume power by transferring data to the circuit for driving the liquid-crystal display panel; large numbers of lower-power liquid-crystal matrix-type display devices configured in this way have been used in mobile telephones in recent years.
Low-cost STN (super-twisted birefringent) liquid-crystal panels with built-in frame memories as described above, which are still lower in power consumption, have frequently been used as liquid-crystal display panels for mobile telephones. However, a videophone function is expected to be added in the future, together with the start of moving-picture distribution service conforming to the IMT-2000 standard. A moving-image display will then be necessary, and since the conventional STN liquid-crystal panel has inadequate response speed, a changeover to display panels that support moving-image displays is foreseen for mobile telephones. Specifically, it is foreseen that active-matrix liquid-crystal panels such as TFT (Thin Film Transistor) liquid-crystal panels and MIM (Metal Insulator Metal) liquid-crystal panels, which have a high response speed and good image quality, will be primarily used.
The active-matrix liquid-crystal panels that are expected to be used in the future are not, in general, as low in power consumption as the STN liquid-crystal panels that have been used in the past. Active-matrix liquid-crystal panels with power consumption reduced to a level permitting use in mobile telephones have been developed in recent years, however.
As for STN liquid-crystal panels, although their future use has become uncertain because of their comparatively slow response speed, fast-response STN liquid-crystal panels with response speeds increased to enable the display of moving images are being developed.
Organic electroluminescent (EL) panels, which employ a display method in which the picture-element section itself is made to emit light, have a much faster response speed than liquid-crystal panels, and since these displays panels are of the self-luminous type, they do not require illumination such as back-lighting or front-lighting, so their power consumption is not very high. Accordingly, organic EL display panels are considered suitable as display panels for mobile telephones because they can be slimmed and lightened by the amount taken up by back-lighting or other illumination.
The general response speeds of the display panels described above are about 300-500 msec for the STN liquid-crystal panels that have been used in mobile telephones, about 30-50 msec for an active-matrix liquid-crystal panel such as a TFT, about 70-80 msec for a fast-response STN liquid-crystal panel, and on the order of several microseconds for an organic EL panel.
FIG. 9
is a block diagram showing the structure of a conventional matrix-type display device with a built-in frame memory.
In the matrix-type display device
9
in
FIG. 9
, reference numeral
70
denotes an input control section that controls the timing etc. of input image data, and reference numeral
80
denotes a display-panel module that displays the input image data.
The input control section
70
has a graphics memory
11
that can temporarily store input image data at least in frame units, a data-write control circuit
12
comprising a microprocessor or the like with an address bus, a data bus, control signal lines, and the like, that carries out control when the input image data are written in the graphics memory
11
, and a data-read control circuit
13
that reads the image data temporarily stored in the graphics memory
11
and transfers the data to the display-panel module
80
.
The display-panel module
80
has: a frame memory
21
that can store image data transferred from the input control section
70
in at least frame units; a display panel
22
in which picture-element units are provided at intersections in a matrix formed by a plurality of signal lines laid out in parallel columns and a plurality of signal lines laid out in parallel rows; a signal-electrode driving circuit
23
that generates a clock signal as a reference for displaying an image on the display panel
22
and, based on the clock signal, generates control signals for reading image data from the frame memory
21
and driving the signal lines of the display panel
22
, and generates a frame synchronization signal and a line synchronization signal of the display panel
22
; and a scan-electrode driving circuit
24
that generates control signals based on the frame synchronization signal and line synchronization signal to drive the scanning lines of the display panel
22
. The display panel
22
is, for example, a liquid-crystal display panel with liquid-crystal display elements disposed in a matrix array.
The image data input to the matrix-type display device
9
from the outside and written in the graphics memory
11
are GD
1
; the image data read from the graphics memory
11
and transferred to the frame memory
21
are GD
2
; the image data read from the frame memory
21
and input to the signal-electrode driving circuit
23
are GD
3
. The frame synchronization signal output from the signal-electrode driving circuit
23
to the scan-electrode driving circuit
24
is FS; the line synchronization similarly output from the signal-electrode driving circuit
23
to the scan-electrode driving circuit
24
is LS; the read control signal likewise output from the signal-electrode driving circuit
23
to read the stored contents of the frame memory
21
is RC.
The operation of the matrix-type display device
9
will be described with reference to the image-data transfer timing diagram in
FIG. 10
, as well as to FIG.
9
.
Image data GD
1
are input to the input control section
70
of the matrix-type display device
9
from the outside by a communication function or the like and stored temporarily in the graphics memory
11
under control of the data-write control circuit
12
. When the process of storing the image data GD
1
in the graphics memory
11
ends at timing t1, those image data are immediately read out by the data-read control circuit
13
and transferred to the frame memory
21
as image data GD
2
, as shown in FIG.
10
.
In the display-panel module
80
, the image data stored in the frame memory
21
are read out periodically by the signal-electrode driving circuit
23
as image data GD
3
, in a refresh cycle based on an independently generated clock signal, as shown in
FIG. 10
, and are input to the signal-electrode driving circuit
23
. Using the independent clock, the signal-electrode driving circuit
23
generates the read control signal RC and sends it to the frame memory
21
, generates and outputs control signals for the signal electrodes of the matrix display panel
22
, and gener
Nakatani Hidehiko
Sugiyama Kazuhiro
Birch & Stewart Kolasch & Birch, LLP
Mengistu Amare
Mitsubishi Denki & Kabushiki Kaisha
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