Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2002-01-24
2004-06-08
Liang, Regina (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S088000, C345S089000, C345S092000, C345S094000, C345S096000, C345S098000, C345S100000, C345S205000, C345S206000, C345S207000, C345S208000, C345S209000, C345S211000, C345S212000
Reexamination Certificate
active
06747622
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device which can reduce driving power for cell selection and a method for driving the liquid crystal display device.
2. Description of the Related Art
In a liquid crystal display device which uses an STN (Super Twisted Nematic) type liquid crystal panel, pixel driving signals, that is, driving signals for selecting respective cells of the liquid crystal panel include segment signals which constitutes selection signals (scanning signals) and another segment signals indicative of display data. These driving signals are supplied as so-called alternating signals which have respective potentials thereof inverted periodically.
FIG. 14
is a schematic view for explaining a driving system of a passive matrix type liquid crystal panel which represents an STN (Super Twisted Nematic) type liquid crystal panel. The liquid crystal panel LCD forms pixels, that is, cells at portions where a plurality of common electrodes COM which are formed in the left-and-right direction in the drawing and a large number of segment electrodes SEG which are formed in the up-and-down direction intersect each other.
Scanning signals (common signals) are applied to respective common electrodes COM from a common scanning circuit and display signals (segment signals) are applied to respective segment electrodes SEG from a segment scanning circuit, thus enabling the pixels at the portions where both electrodes intersect each other to perform the display. A control circuit CONT generates display control signals in response to display signals, control signals and a power source supplied from external input terminals and applies given signals to a common scanning circuit COMD and a segment scanning circuit SEGD.
FIG. 15A
to
FIG. 15C
are explanatory views of driving waveforms for the STN type liquid crystal panel of the related art, wherein
FIG. 15A
is a schematic view for explaining an example of an electrode arrangement structure of the common electrodes COM and the segment electrodes SEG which form the cells and FIG.
15
B and
FIG. 15C
show waveform examples of the driving signals.
FIG. 16
is a circuit diagram for generating the driving waveforms shown in FIG.
15
B and
FIG. 17
is a circuit diagram for generating the driving waveforms shown in FIG.
15
C.
In the electrode arrangement shown in
FIG. 15A
, the respective cells of the liquid crystal panel are formed by eighty pieces (first line to eightieth line) of common electrodes COM
1
, COM
2
, . . . COMn, COMn+1, . . . COM
80
and 384 pieces of segment electrodes SEG
1
, SEG
2
, . . . SEGm, SEGm+1, . . . SEG
384
.
For example, focusing on the neighboring common electrodes COMn and COMn+1, with respect to the driving waveforms
1
of the conventional technique shown in
FIG. 15B
, the driving signals applied to the common electrodes COMn and COMn+1 are formed independently from each other.
That is, when the common electrode COMn of nth line is selected at a certain timing and thereafter the common electrode COMn+1 of (n+1)th line is selected at a next timing, a voltage supplied to the common electrode COMn is changed over from a selection voltage to a non-selection voltage, while a voltage supplied to the common electrode COMn+1 is changed over from a non-selection voltage to a selection voltage.
In an output circuit shown in
FIG. 16
which outputs the driving waveforms
1
shown in
FIG. 15B
, Va indicates a first level voltage (high level) which is outputted from the control circuit CONT, Vb indicates a second level voltage (low level) which is outputted from the control circuit CONT, ca
1
, ca
2
, . . . caN indicate common electrode selection signals, and SWa
1
and Swb
1
, Swa
2
and Swb
2
, . . . SWaN and SwbN indicate a plurality of pairs of analogue switches which generate outputs ct
1
to ctN to the common electrodes COM
1
, COM
2
, . . . COMn.
Although the common electrodes are indicated by COM
1
, COM
2
, . . . COMn, COMn+1, . . . COM
80
in
FIG. 15A
, to simplify the explanation, the explanation is made hereinafter by indicating the common electrodes with 1 to n. Accordingly, the common electrode COMn indicates COMn, COMn+1, . . . COM
80
shown in
FIG. 14
in a representing manner.
A plurality of pairs of analogue switches SWa
1
and Swb
1
, Swa
2
and Swb
2
, . . . and SWaN and SWbN apply the output signals ct
1
to ctN to the common electrodes
1
to n corresponding to the output signals ct
1
to ctN by inputting the first level voltage Va, the second level voltage Vb and the common electrode selection signals ca
1
, ca
2
, . . . caN outputted from the control circuit CONT.
In performing the sequential changeover of such voltages, the voltage level of the selected common electrode COMn and that of the selected common electrode COMn+1 shown in
FIG. 15B
, for example, have polarities inverse to each other. At this point of changeover time, a state in which the charge of the common electrode COMn is fully discharged is established so that a given charge is applied to the common electrode COMn+1 from the non-selected level to the selected level without depending on the voltage level of the common electrode COMn.
Due to such a charging operation, the electric current is consumed so that the liquid crystal panel suffers from the undesired power consumption.
To improve this situation, as shown in
FIG. 15C
, there has been known a method in which the neighboring common electrodes COMn and COMn+1 are short-circuited at the time of changeover of the voltages.
FIG. 17
is a circuit diagram of a driving system shown in
FIG. 15
c
for short-circuiting the neighboring common electrodes at the timing of changing over the common electrodes.
In
FIG. 17
, swc
1
to swcN indicate analogue switches and cb
1
to cbN indicate short-circuit signals for controlling the analogue switches swc
1
to swcN, wherein symbols used in
FIG. 17
which are as same as symbols used in
FIG. 16
indicate parts having same functions.
In this system, as shown in
FIG. 15C
, when the currently selected common electrode is changed over to the non-selection state and the next common electrode is changed over to the selection state from the non-selection state, the currently selected common electrode and the next selected common electrode are short-circuited by the analogue switches swa
1
to swcN.
With the provision of such a system, the neighboring common electrodes can hold the mean charge so that the charging current which is supplied to the next selected common electrode is reduced thus achieving the reduction of power consumption. The detailed operation of the above-mentioned output circuit is disclosed in Japanese Laid-open Patent Publication 194314/1999.
SUMMARY OF THE INVENTION
In the liquid crystal display device which uses this kind of liquid crystal panel, it is necessary to alternate the applied voltage so that the direct current voltage is not applied to the liquid crystal panel.
FIG. 18
is a driving waveform chart for explaining problems derived from an alternation driving of a conventional technique. In the drawing, FLM indicates a frame signal, M indicates an alteration signal and CL
1
indicates latching pulses. Symbols used in
FIG. 18
which are as same as symbols used in
FIG. 15
indicate parts having same functions.
As shown in
FIG. 18
, at the timing of the latching pulse CL
1
, a certain common electrode is selected, and the certain common electrode and another common electrode adjacent thereto (a common electrode to be selected next to the certain common electrode) are short-circuited at the timing of this selection.
However, for example, when the common electrode COMn−1 and the COMn are short-circuited at the timing of the latch pulse n and the common electrode COMn and the COMn+1 are short-circuited at the timing of the latch pulse n+1, the consumptive electricity is increased on the contrary.
Due to t
Kishino Akifumi
Matsudo Toshimitsu
Takahashi Hiroyuki
A. Marquez, Esq. Juan Carlos
Fisher Esq. Stanley P.
Liang Regina
Nguyen Jennifer T.
Reed Smith LLP
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