Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
1999-02-03
2004-07-06
Wu, Xiao (Department: 2674)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S094000, C345S095000, C345S210000, C345S100000, C345S098000
Reexamination Certificate
active
06760018
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a matrix-type liquid-crystal display apparatus (hereinafter referred to as an liquid-crystal display), and more specifically it relates to a scanning electrode drive apparatus which drives a liquid-crystal display and a method of drive associated therewith.
BACKGROUND ART
In recent years, with advances in information-oriented societies, liquid-crystal displays have come into use in a wide range of fields, such as in TVs and in office equipment. In compact portable equipment in particular, liquid-crystal displays have come into overwhelming widespread use, compared with other types of displays.
In these types of fields, because of the high importance of portability, while compactness is demanded, a larger screen is required to assure readability. For this reason, there is a great need to increase the display region within a limited area, this being accompanied by an ever-narrowing area surrounding the liquid-crystal display.
One method to cope with accommodating narrowed area surrounding the display is to slim-down and make small the scanning electrode drive device and signal electrode drive device, and one method of achieving a slimmed-down and smaller scanning electrode drive device and signal electrode drive device is to make the withstand voltage small so as to shrink the element size.
In the method used in the past, as shown in
FIG. 4
, was to change the potential when the liquid-crystal display operates by AC, the scanning electrode device outputting the combinations of V
1
/V
2
and V
3
/V
4
, the signal electrode drive device outputting the combinations of V
5
/V
4
and V
1
/V
6
at those respective times.
Therefore, for both the scanning electrode drive device and the signal electrode drive device, a withstand voltage of at least V
1
-V
4
was required, making it necessary to use an electrode drive device with a high withstand voltage.
In this method, it is necessary to implement the signal electrode drive device as well using elements having a high withstand voltage, this being incompatible with the achievement of compactness and high density.
This is also disadvantageous and not compatible with an increase in the speed of operation of the signal electrode scanning device accompanying an increase in the number of data signals that are required for an increased number of pixels.
Additionally, because a high voltage must be operated at high speed, the associated power consumption is not very low.
One method of solving the above-noted problems is to use a drive method which makes use of power supply voltage swinging method.
This power supply voltage swinging method is that method whereby, as shown in
FIG. 5
, a potential VB which is switched from potential VA, as grounding potential, is input to the scanning electrode drive device, while in synchronization with which, a potential VD which is switched from potential VC, as high level voltage potential, is also input to the scanning electrode drive device, respectively.
By doing this, it is possible to greatly lower the withstand voltage of the signal electrode drive device without increasing the withstand voltage of the scanning electrode drive device, the result being that it is possible to achieve a increased operating speed in the signal electrode drive device due to an increase in the number of data signals, and also to achieve high density and low power consumption.
However, using the power supply undulation method, in the case in which a signal from an external system is input to the scanning electrode drive device, when the power supply potential is in the period A condition as shown in
FIG. 5
, within the scanning electrode drive device there is a low-level input when the input signal is at the VB level and a high-level input when the input signal is at the VD level. Also, when the power supply potential is in the period B condition, within the scanning electrode drive device there is a low-level input when the input signal is at the VA level and a high-level input when the input signal is at the VC level.
For this reason, in the case in which a signal is input from an external system, depending upon the condition of the power supply potential, it is necessary to input the VD level or the VC level in the case of inputting a high level, and necessary to input the VB level or the VA level in the case of inputting a low level.
For this reason, it is necessary to change the potential of an externally input signal, this making it necessary to have an external circuit that converts the input signal potential.
An example of a drive circuit of a liquid-crystal display which uses the above-noted power supply undulation method will now be described, with reference being made to FIG.
6
.
Specifically, a drive circuit
200
for a liquid-crystal display which uses the power supply voltage swinging method (referred to the voltage swinging method hereafter) of the past has signal electrode drive circuits
203
that drive the signal electrodes of the liquid-crystal display
202
and scanning electrode driving circuits
204
that drive the scanning electrodes that are provided in a direction that perpendicularly intersects the above-noted signal electrode drive circuits.
More specifically, this drive circuit
200
has a swinging voltage generating circuit
206
that generates a swinging voltage and supplies this swinging voltage to the above-noted scanning electrode driving circuits
204
, a level-converting circuit
207
that is connected to the above-noted swinging voltage generating circuit
206
and the above-noted scanning electrode driving circuits
204
, that is connected to an input signal (sign), and that is provided for the purpose of converting this input signal, which is input via an appropriate signal input means
208
, to the above-noted swinging voltage level, and a controller
205
that separately controls the above-noted signal electrode drive circuits
203
, swinging voltage generating circuit
206
, and level-converting circuit
207
.
In the above-noted drive circuit for a liquid-crystal display that uses the voltage swinging method of the past, it is necessary to use an input signal such that coincides with the difference in potential between the high-level voltage (VDD) and the low-level voltage (VSS) output from the above-noted swinging voltage generating circuit
206
.
Therefore, in a drive circuit for the liquid-crystal display of the past as described above, as shown in
FIG. 7
, the actual input signal (sign; indicated by a thick broken line in the drawing) is generated by voltage conversion so as to vary as shown by the thick line in the drawing (signV).
Therefore, in a drive circuit for a liquid-crystal display in the past, it is minimally required that the above-noted level-converting circuit
207
be provided, and there is the problem that this makes it difficult to achieve a downsizing of the overall drive circuit of this liquid-crystal display.
Additionally, as seen from the scanning electrode drive device, it is not necessary to have the overall circuit have a high withstand voltage, and on the contrary, it is desirable that in particular, a portion which processes controlling signals, other than output signals for driving a liquid crystal, is composed by devices having a low withstand voltage from the standpoint of low power consumption and compactness.
However, in the currently used configuration that employs the voltage swinging method, implementation using a low withstand voltage circuit is difficult.
An object of the present invention is to improve on the above-noted prior art, and to provide a circuit capable of direct input of an input signal the level of which is fixed, without shifting the level of the input signal while employing the voltage swinging method.
DISCLOSURE OF THE INVENTION
To achieve the above-noted object, the present invention employs the basic technical constitution described below. Specifically, a first aspect of the present invention is a liquid-crystal display drive circuit having a signal electrode driver whi
Citizen Watch Co. Ltd.
Nguyen Kevin
Wu Xiao
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