Computer graphics processing and selective visual display system – Display driving control circuitry
Reexamination Certificate
2002-01-08
2004-09-21
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Display driving control circuitry
Reexamination Certificate
active
06795066
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to reduction of electricity consumption of a matrix-type display apparatus.
BACKGROUND OF THE INVENTION
Recently, there has been a rapid acceleration in application of liquid crystal display apparatuses in apparatuses, such as word processors, lap top-type personal computers, and pocket-sized televisions. Among the liquid crystal display apparatuses, especially, a reflection-type liquid crystal display apparatus (LCD) draws an attention. Because display of the reflection-type LCD is carried out by reflecting incident light from an outside, the reflection-type LCD requires no back light, thus contributing to low electricity consumption and thin thickness, which leads to a light weight of apparatuses using the LCD of the reflection type.
Conventional LCDs of the reflection type are broadly classified into (a) one using a segment display method, (b) one using a simple multiplex driving method, and (c) one using an active matrix driving method. By using the segment display method, it is possible to display only simple numbers or pictorial symbols, which are used in watches and the like. The simple multiplex driving method and the active matrix driving method, which uses an active element such as a Thin Film Transistor (TFT), can be used for complicated displays of personal computers, portable information terminals and the like. It is desired commonly for all the three methods to have a lower electricity consumption.
As a method of reducing the electricity consumption of the segment display method, Japanese Unexamined Patent Application, Tokukaihei, No. 5-232447 (published on Sep. 10, 1993) discloses that identical potential is applied into a common electrode and a segment electrode so as to acquire a stable display totally in white or black color during a standby time, that is, while no image is displayed and displayed is an all-while display or an all black-display. Moreover, Japanese Unexamined Patent Application, Tokukaihei, No. 2-210492 (published on Aug. 21, 1990) discloses a method for making a high impedance state in an MOS transistor, which directly drives a liquid crystal during the standby time, so that electricity consumption of a driving circuit is reduced. Because the prior arts are for the LCD using the segment display method, the prior arts are limited to display the simple numbers and pictorial symbols, and cannot be applied to those apparatuses such as the personal computers and the portable information terminals, which display complicated information.
Furthermore, it is difficult to employ those driving methods in a matrix-type liquid crystal display apparatus. Going into details, for example, a matrix-type LCD of 4×4 size as shown in
FIG. 15
have scanning signals as shown in FIG.
16
. The scanning signals are respectively supplied to scanning signal lines G(
0
) to G(
3
), so that a selective voltage is applied in order into the scanning signals G(
0
) to G(
3
). In a synchronizing manner with the scanning signals of the thus selected respective scanning lines, data signals are supplied to data signal lines S(
0
) to S(
3
), so as to write in each pixel an electric charge, which is in accordance with a data. After scanning of a bottom line and a vertical blanking period of a short time, scanning is started again from a first line, as shown in FIG.
17
. An original reason why the vertical blanking period is provided is to have a period during which an electron beam from an electron gun, which is provided inside a CRT, can return to its original position. Therefore, LCDs actually requires no vertical blanking period. However, in order to reproduce a general television image or the like on LCDs, the vertical blanking period is provided to LCDs so as to give a compatibility to LCDs with respect to television images according to NTSC (National Television System Committee) or the like.
As discussed above, in case of the matrix-type LCD, it is necessary to drive plural pixels on data signal lines aligned in a vertical direction on a screen. Thus, the matrix-type LCD has no such data signal output to drive single pixel alone, unlike a segment output of the segment display method. Therefore, although application of a driving method of the segment display method in the matrix-type LCD keeps the data signal lines and opposite electrode of the pixels at the high impedance state after electric charges are written in pixels on a bottom line on one picture (one picture in one frame), the pixels other than the pixels in a bottom line of the screen does not maintain an electric charge written therein, thereby failing to achieve a stable display on the matrix-type LCD.
Among such matrix-type LCDs, a matrix-type LCD using the simple multiplex driving method has a size of 2-inch and consumes electricity in a range of from 10 mW to 15 mW, which is sufficiently small. However, the matrix-type LCD of the simple multiplex driving method is disadvantaged in its low brightness and contrast and slow responding speed, which are fundamental display qualities. On the other hand, the matrix-type LCD employing the active driving method, in which the TFT or the like is used, is excellent in brightness and contrast, and has a fast responding speed, thereby being satisfactory in terms of the fundamental display qualities. However, even the matrix-type LCD of 2-inch size consumes electricity in a range of from 100 mW to 150 mW, which is unsatisfactorily high.
In view of the above problems, intensive research and developments have been carried out, aiming to attain sufficiently low electricity consumption and good display qualities. For example, Japanese Unexamined Utility Model Application, Jitsukaisho, No. 60-50573 (published on Apr. 9, 1985), and Japanese Unexamined Patent Application, Tokukaihei, No. 10-10489 (published on Jan. 16, 1998) disclose methods of achieving low electricity consumption. The methods in those publications, taking note of how television signals are transmitted, take advantage of the vertical blanking period, during which no data exists, so as to stop operation of a peripheral driving circuit during the vertical blanking period, thereby reducing the electricity consumption.
Moreover, another method is disclosed in Japanese Unexamined Patent Application, Tokukaihei, No. 9-107563 (published on Apr. 22, 1997), which relates to reduction of electricity consumption of a head mounting-type display apparatus for field sequential three-dimensional (3-D) image display, having two liquid crystal panels respectively for each eye. In this method, only one of the liquid crystal panels is driven during one field, while the other is stopped operating during the one field. In this way, the liquid crystal panels are driven in turn per field period.
As still another method, SID′ 95 symposium digest, pages 249 to 252 (Titled: Multi-Field Driving Method For Reducing LCD Power Consumption) and Japanese Unexamined Patent Application, Tokukaihei, NO. 3-271795 (published on Dec. 3, 1991) discuss a multi-field driving method, in which scanning of one picture is carried out in such a manner that every other scanning signal line or every other several scanning signal lines are scanned so that scanning is performed in installment (that is, not at once, but divided into a plurality of times). In one time (one of the divided plurality of times) of the scanning, a voltage in the data signal line is not inverted (changed) in terms of polarity, thereby reducing electricity consumption of a data signal line driver. Moreover, this method also aims to realize a display free from flickering as a whole, by cancelling out flickering on one line with flickering on a neighboring line thereof. The flickering is changes of brightness caused between each line, and flickering on each line has an opposite polarity with respect to flickering on neighboring lines thereof.
Furthermore, for example, Japanese Unexamined Patent Application, Tokukaihei, No. 6-342148 (published on Dec. 13, 1994) discloses a method in which a ferroelectric liquid crystal is
Nagata Hisashi
Tanaka Kyoushi
Conlin David G.
Edwards & Angell LLP
Hjerpe Richard
Jensen Steven M.
Laneau Ronald
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