Computer graphics processing and selective visual display system – Display driving control circuitry
Reexamination Certificate
1999-05-06
2002-05-28
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Display driving control circuitry
C345S050000, C345S087000, C345S090000, C345S096000, C345S098000, C345S099000, C345S100000, C345S208000, C345S212000, C345S214000
Reexamination Certificate
active
06396485
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a display apparatus with a drive circuit, and more specifically, to a line inverting drive type display apparatus with a drive circuit in which power consumption can be reduced.
2. Description of the Related Art
A display apparatus such as a liquid crystal display (LCD) apparatus is widely used in various electronic appliances such as mobile communication terminals. A long time operation is required in the display apparatus using a battery. Therefore, power consumption required to drive the display apparatus should be reduced.
As typical liquid crystal display (LCD) drive systems, a line inverting drive system and a frame inverting drive system are well known in the field. In both LCD drive systems, a polarity of voltage applied between electrodes is switched at a timing when a line or a frame is switched. The reason why the switching of polarity of applied voltage is required is given as follows. That is, when a voltage having the same polarity is continuously applied to a LCD cell, a characteristic of the LCD cell is deteriorated.
FIGS. 1A
to
1
D are timing charts showing electrode drive timing performed in accordance with the line inverting drive system. In the line inverting drive system, the polarity of a voltage applied between a common electrode and a segment electrode is inverted for every scanning line. Similarly,
FIGS. 2A
to
2
C are timing charts showing electrode drive timing in the frame inverting drive system. In the frame inverting drive system, the polarity of a voltage applied between a common electrode and a segment electrode is inverted for every field. In the figures, symbol COMm (symbol “m” is an integer) shows the voltage level of the common electrode, and symbol SEGn (symbol “n” is an integer) represents the voltage level of the segment electrode. In
FIGS. 1A
to
1
D and
FIGS. 2A
to
2
C, the respective voltage levels are indicated over two frame periods.
Japanese Laid Open Patent Application (JP-A-Heisei 4-67122) describes the technique in which a flicker problem can be eliminated and also a transistor element can be made compact in the LCD element drive system. Also, Japanese Laid Open Patent Application (JP-A-Heisei 8-76083) describes the technique in which a stable operation period can be made long and also a cross-talk can be reduced in the LCD drive apparatus. Furthermore, Japanese Laid Open Patent Application (JP-A-Heisei 9-230829) discloses the technique of a source driver output circuit for driving for a short time in a high power usage efficiency. In addition, Japanese Laid Open Patent Application (JP-A-Heisei 9-236790) describes the technique for reducing a cross-talk in the LCD display device.
FIG. 3
is a block diagram showing a conventional liquid crystal display (LCD) drive circuit of the line inverting drive system. The conventional LCD drive circuit is composed of a power supply circuit
201
, a timing generator
203
, a common electrode selecting circuit
205
, a common signal generating circuit
207
, a segment signal generating circuit
209
, a first switch unit
211
, and a second switch unit
213
.
The first switch unit
211
is composed of switch pairs corresponding to common electrodes, respectively. The different voltages are applied to each of switches SWDm and SWEm of each switch pair. The second switch unit
213
is composed of switch pairs corresponding to segment electrodes, respectively. The different voltages are applied to each of switches SWFn and SWGn of each switch pair.
FIGS. 4A
to
4
F are timing charts of the LCD drive circuit shown in FIG.
3
. The timing generator
203
divides a clock signal
215
of
FIG. 4A
in frequency to produce a frequency-divided clock signal
217
, as shown in FIG.
4
B. The frequency-divided clock signal
217
specifies line inverting drive timing.
In response to the frequency-divided clock signal
217
, the first switch unit
211
and the second switch unit
213
may switch each of the switch pairs. For example, when the common electrode COM
1
is selected in a selection period “t2” of
FIG. 4D
, the voltage applied to the common electrode COM
1
changes at the line inverting timing “t1”, as shown in FIG.
4
E. Similar to the common electrode, the voltage applied to the segment electrode is changed. It should be noted that only segment electrode “SEG1” is shown in FIG.
4
F.
In the liquid crystal display apparatus of the line inverting drive system, the polarity of the voltage applied between the electrodes is inverted for every line. At the timing “t1” when the polarity is inverted, charges stored between the electrodes are previously discharged. Also, the power is consumed based on the voltage level required to be inverted.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a display apparatus with a drive circuit in which power consumption can be reduced.
Another object of the present invention is to provide a liquid crystal display drive circuit in which power consumption can be reduced at a timing when the polarity of a voltage applied between electrodes is switched.
Still another object of the present invention is to provide a liquid crystal display drive circuit in which power consumption can be reduced by adding a simple circuit.
In order to achieve an aspect of the present invention, a display apparatus includes a display panel and a logic switch unit. The display panel has a plurality of common electrodes and a plurality of segment electrode arranged in a direction orthogonal to the plurality of common electrodes. Display cells are formed at intersections of the plurality of common electrodes and the plurality of segment electrodes. The logic switch unit short-circuits selected ones of the plurality of common electrodes corresponding to a display cell group and selected ones of the plurality of segment electrodes corresponding to the display cell group in response to a common-segment short-circuit timing signal. The display cell group includes selected ones of the display cells.
The logic switch unit preferably short-circuits the selected segment electrodes in response to a segment short-circuit timing signal, before the selected common electrodes and the selected segment electrodes are short-circuited.
Also, a number of the selected common electrodes is 1, and the common-segment short-circuit timing signal is generated before a line inverting operation to the common electrode.
The common-segment short-circuit timing signal is generated such that electric charge stored between the selected common electrode and the selected segment electrodes is redistributed.
It is preferable that the selected common electrode is electrically disconnected from the selected segment electrodes, when the stored charge substantially reaches a preset value.
In order to achieve another aspect of the present invention, a liquid crystal display drive circuit for driving a display panel which has a plurality of common electrodes and a plurality of segment electrode arranged in a direction orthogonal to the plurality of common electrodes. The liquid crystal display drive circuit includes a timing control unit, a common electrode driving unit, a segment electrode drive unit and a logic switch unit. The timing control unit frequency-divides a clock signal to generate a first timing signal and a second timing signal from the frequency-divided clock signal, and inputs a display data to output a segment data corresponding to the plurality of segment electrodes. The common electrode drive unit generates a common selection signal based on the frequency-divided clock signal and the first timing signal to select one of the plurality of common electrodes. Also, the common electrode drive unit generates a common drive signal used to drive the selected common electrode with a selected one of a plurality of first levels. The segment electrode drive unit generates a segment drive signal used to drive each of the plurality of segment electrodes with a selected one of a plurality of second l
Hjerpe Richard
NEC Corporation
Tran Henry N.
Young & Thompson
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