Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-04-17
2002-12-17
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S100000, C345S214000
Reexamination Certificate
active
06496174
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of driving a display device, a display device and an electronic apparatus and, in particular, to a technique for reducing the power consumption of the display device.
BACKGROUND ART
Since passive matrix type liquid-crystal display devices need no costly switching elements and are less expensive than active matrix type liquid-crystal display devices, the passive matrix type liquid-crystal display devices find widespread use as monitors of portable computers and portable electronic apparatuses.
The following methods are known as the methods of driving the passive matrix type liquid-crystal display device.
(1) APT method (IEEE TRANSACTIONS OF ELECTRON DEVICE, VOL, ED-21, No.2, FEBRUARY 1974 P146-155 “SCANNING LIMITATIONS OF LIQUID-CRYSTAL DISPLAYS” P. ALT, P. PLESHKO, ALT&PLESHKO TECHNIC).
(2) Smart Addressing (LCD International '95, Liquid-Crystal Display Seminars held under the sponsorship of Nikkei BP, C-4 Lecture No. (1), by Matsushita of Tottori SANYO Electric, Co., Ltd).
(3) Multi-line driving methods (for example, Japanese Patent Application 4-84007, Japanese Unexamined Patent Publication No. 5-46127, and Japanese Unexamined Patent Publication No. 6-130910).
Besides the demand for miniaturization and light weight, there is a growing demand for longer time of displaying without the need for battery replacement in the field of the portable electronic apparatuses such as cellular telephones and pagers. Therefore, a low power consumption feature is rigorously required of the display device used in such portable electronic apparatuses.
The inventor of this invention has extensively studied the passive matrix type liquid-crystal display device with a view to reducing power consumption.
The study has shown that prior art passive matrix liquid-crystal display devices have to supply an alternating current of 20 V or higher in amplitude to both scanning lines and signal lines even during a display-off time, that the power consumption in the power supply circuit for generating that alternating current is considerably large, and that currents flowing between the scanning lines and the data lines via liquid crystals are also considerably large.
The present invention has been developed with a view to resolving such problems.
DISCLOSURE OF INVENTION
One of the primary objects of the present invention is to reduce power consumption of a display device such as a passive matrix type liquid-crystal display device.
In a preferred embodiment of the display device of the present invention, the number of voltage levels of scanning lines during a non-selection period is only one, and to set a display element to a display-off state, the voltage level of the data line corresponding to that display element is set to the voltage level of the scanning lines during a non-selection period.
In such a driving method, if image presentation is performed with the polarity of the selection voltage to the scanning lines being periodically alternated, the voltage level during a non-selection period remains unchanged (at a single level) regardless the polarity of the selection voltage for the scanning lines. By employing the voltage level of the data line as the non-selection voltage level of the scanning line, display-off state is easily performed.
The display-off state means a disabled state of the display. The screen of the display-off state corresponds to the screen in a display-off mode. The display-off mode is a mode available to achieve an extremely low power consumption. In the description that follows, the terms “display-off state”, “display-off mode”, and “display-off mode screen” are frequently used.
In the present invention, when a scanning line is set to a non-selection voltage with a data line set to the same voltage, no voltage difference between both lines appears activating a display-off state (display-off mode).
Since the number non-selection voltage levels is only one, the power supply circuit for generating the non-selection voltage is simple, and the power consumption of the power supply circuit is reduced. Compared with the method where the non-selection voltage is changed periodically, equalizing the data line voltage to the scanning line voltage is easy, and the power consumption with a display panel attributed to the voltage difference between the scanning line and the data line is reduced. Thus, power consumption of the display device is accordingly reduced.
Even when a selection pulse enters the scanning line with the voltage level at the data line kept to the non-selection voltage level of the scanning line, the display-off state is maintained. This is because simply selecting a scanning line during a selection-period is not sufficient enough to exceed the threshold of liquid crystal and keeps the display-off state.
Based on this principle, one area in one screen is set to the display-off mode while the remaining area is allowed to present a predetermined image such as icons by controlling properly the voltage applied to the data line.
In a preferred embodiment of the present invention, a display control signal is applied to each of a plurality of ICs to drive the data lines, and by the display control signals, at least parts of data line drive outputs from the ICs are set to the voltage level of the scanning lines during a non-selection period.
A plurality of ICs are arranged as data line drivers, and the data line drive outputs from the ICs on a per IC basis is kept to the voltage level of the scanning lines during the non-selection period. In this way, the area covered by that IC is set to the display-off state (display-off mode).
In a preferred embodiment of the present invention, when at least parts of data line drive outputs are set to the voltage level of the scanning lines during the non-selection period, the supply of, at least, either display data or a high-frequency clock for transferring the display data to the IC is suspended.
By suspending the display data in the area in display-off state (the area in the display-off mode) or the high-frequency clock to be used for the transfer of the display data, low power consumption design-is further promoted.
In a preferred embodiment of the present invention, a display control signal is applied to the driving circuit for the data lines to individually control the data-line drive outputs and to selectively set a desired drive output to the voltage level of the scanning lines during the non-selection period.
With this arrangement, the area in the display-off state is flexibly set.
In a preferred embodiment of the present invention, the data-line driving circuit, constructed of a plurality of blocks, is supplied with the display control signal, which controls the data line drive outputs on a block by block basis so that the data line drive outputs within any block are set to the voltage level during the non-selection period.
In this way, the area in display-off state is flexibly set on a block by block basis.
In a preferred embodiment of the present invention, h scanning lines out of the plurality of scanning lines (h is an integer equal to or greater than 2) are simultaneously selected, and each of the selected scanning lines is supplied with a scan voltage based on a predetermined selection voltage pattern, while each of the data lines is supplied with a voltage that is determined by comparing the selection voltage pattern with the display data representative of the display status of each display element so that a desired display is presented, and to activate no image presentation state (display-off mode screen), the display control signal fed to the data-line driving circuit sets, at least, parts of the data line drive outputs to the voltage level of the scanning lines during the non-selection period.
The driving method of activating the display-off state (display-off mode screen) is applied to a display device which features a known multi-line driving technique.
In this case, along with the advantage of the multi-line driving method that the level of the selection vol
Ikeda Masuhide
Isozaki Shingo
Ito Akihiko
Katase Makoto
Kurumisawa Takashi
Harness & Dickey & Pierce P.L.C.
Said Mansour M.
Shalwala Bipin
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