Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
1999-01-27
2001-10-16
Hjerpe, Richard (Department: 2774)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S212000, C345S213000
Reexamination Certificate
active
06304256
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a display unit such as a liquid crystal display. Particularly, the invention relates to controlling display voltages generated by a drive circuit.
2. Description of the Related Art
Recently, electronic devices such as a telephones or personal computer have began to incorporate device a display. Particularly, portable devices such as note-book type personal computers, portable telephones unit or portable television have become quite popular now. Each of these types of portable devices may include a liquid crystal display (hereinafter called “LCD”).
The LCD has a LCD drive circuit to drive a display portion as display circuit. The LCD drive circuit generates a plurality of display voltages that are used by the display circuit. These display voltages are generated by activatting a booster circuit. For example, the booster circuit generates these display voltages based on a supply voltage supplied by a supply voltage source.
The booster circuit is popular to charge a pump system. For this case, the booster circuit has a capacitors store electrical charges used to charge a voltage source of the display circuit. These capacitors are coupled between corresponding wires and a reference voltage source such as a ground voltage source. Each of the wires transmit a correponding one of these display voltages generated by the booster circuit.
For the LCD drive circuit, when the supply voltage VDD decreases rapidly, electrical charge stored the capacitor does not discharge. Therefore, the wires leave electrical charge stored for a long time. As a result, the display portion of the display circuit leaves display. Thus, there occur instances in which information is displayed carelessly for viewing by a third party and there is a reduction in the life of the display circuit and malfunction or the like occur at restart-up, etc.
Particularly, when the portable device is in operation, the battery is removed without interrupting the power supply by a switch and the charged electrical charge is discharged. Therefore, it is necessary for the portable device to have the above problems solved.
For solving these problems, the solution measures further require more reliable operation when the supply voltage VDD is reduced.
The solution measures further require that there be no interference with a reduction in the size and cost of the display device itself.
SUMMARY OF THE INVENTION
The object of this invention is to provide a display device which can be provided wherein no display is left on the display part used as the display circuit by setting display voltages at a ground voltage level when a source voltage rises.
Another object of this invention is to provide a display device which operates more reliably when the supply voltage VDD is reduced.
A further other object of this invention is to provide a display device which does not interfere with a reduction in the size and cost of the display device itself.
A display device of this invention generates a plurality of display voltages according to a predetermined voltage and displays images by a display circuit according to these display voltages. The display device comprises a display voltage generating circuit that receives the predetermined voltage, and generates the display voltages corresponding to a first control signal; a plurality of wires, each wires transmitting a corresponding one of display voltages; a plurality of charge storage circuits being each charge storage circuits coupled to a corresponding one of the wires; a setting circuit that sets each voltage level of the wires at a predetermined value corresponding to a second control signal; and a monitor circuit supplied with the predetermined voltage, the monitor circuit monitoring a reduction in the predetermined voltage, and outputting another control signal when the monitor circuit senses a reduction in the predetermined voltage.
Typical embodiments of the present application are described herein in brief. However, the various embodiments of the present invention and specific configurations of these embodiments will be understood from the following description.
REFERENCES:
patent: 5323171 (1994-06-01), Yokouchi et al.
patent: 5572735 (1996-11-01), Tanikawa
patent: 5793346 (1998-08-01), Moon
patent: 5838294 (1998-11-01), Praiswater
patent: 5859632 (1999-01-01), Ito
patent: 6005541 (1999-12-01), Takahashi et al.
patent: 7-104711 A (1995-04-01), None
Hjerpe Richard
Nguyen Kimnhung
OKI Electric Industry Co., Ltd.
Rabin & Berdo P.C.
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