Computer graphics processing and selective visual display system – Data responsive crt display control
Reexamination Certificate
1997-08-13
2001-10-16
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Data responsive crt display control
C345S111000
Reexamination Certificate
active
06304235
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an impedance matching circuit, and more particularly to an impedance matching circuit for stably embodying the signal of a wide band frequency range by compensating for the decreasing of the signal due to an RC time constant when supplying video signals input via a BNC or a D-SUB connector to a video amplifier and a display device having the impedance matching circuit.
2. Description of the Related Art
Typically, computer peripheral devices refer to various input/output devices connected to a computer system, such as a monitor, a printer, a CD-ROM, a plotter, etc.
A monitor widely used as a display device of a computer serves to convert input signals into image signals to enable a user to check the operation of the computer. It uses the principle that different amounts of electron beams which vary according to the strength of the image signal hit the fluorescent material of one color of red, green and blue covering the surface of a cathode ray tube (hereinafter referred to as a “CRT”) to emit light of different brightness or different color.
To make a screen adequate to the CRT, the CRT should be properly adjusted to the display device. Generally, voltage and driving waveforms required to drive the monitor are needed. In addition, the monitor requires a mechanical structure to support CRT.
An earlier monitor normally includes a video input unit for inputting video signals generated by a video card in a computer and transmitted via a signal cable, a video amplifier unit for amplifying the video signals supplied via the video input unit and for transmitting them to a CRT, horizontal and vertical deflection circuits for respectively inputting horizontal and vertical synchronization signals transmitted via the signal cable and for performing horizontal and vertical deflection.
A display controller, e.g., a computer, is connected to a monitor via a signal cable for transmitting image and synchronization signals. A coaxial cable is typically used for the signal cable to suppress the radiation of electromagnetic waves and to prevent the signal from unnecessary attenuation.
When an image is output on the monitor by using the signal supplied from the computer, the computer may have various high frequency outputs and low frequency outputs corresponding to the frequency change according to the video card therein.
The signal cable disposed between the computer and the monitor includes a resistance component and a capacitance component.
The resistance and capacitance components together cause the signal and the signal cable to decrease depending upon the time constant of the resistance and capacitance elements. Accordingly, an impedance matching circuit for compensating for the signal decreasing due to resistance and capacitance elements is provided between the video input unit and a video amplifier.
The earlier impedance matching unit consisting of single resistance elements combined with a capacitance element, has a problem that while it can achieve a proper impedance matching effect when the video frequency band is below 200 mega-Hertz (MHz), the compensating effect is significantly reduced when the frequency band is over 200 mega-Hertz.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an impedance matching circuit that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an impedance matching circuit which can compensate for the wide band frequency at its maximum without the loss of input signals.
Another object of the present invention is to provide an impedance matching circuit which can compensate for the decrease of video signals within a wide band frequency range.
Another object of the present invention is to provide an impedance matching circuit which can compensate at its maximum the decrease of red, green and blue video input signals due to the time constant of a resistance and a capacitance.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the object of the present invention, as embodied and broadly described, an impedance matching circuit of a display device having a video input unit for inputting video signals R, G, B supplied from an external device via a signal cable; a video amplifying unit for amplifying the video signals supplied from the video input unit; and an impedance matching circuit connected between the video input unit and the video amplifying unit, for compensating for the decrease of the video signals R, G, B supplied from the external device, comprises a first resistor connected to the video input unit; a capacitor connected in series with the first resistor and connected to the video amplifying unit; and at least second resistors connected in series between a connecting point of the first resistor and capacitor and ground.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 4316220 (1982-02-01), Muterspaugh et al.
patent: 4354163 (1982-10-01), Kato et al.
patent: 4468701 (1984-08-01), Burcher et al.
patent: 5268676 (1993-12-01), Asprey et al.
patent: 5666658 (1997-09-01), Borchartdt et al.
patent: 6094282 (2000-07-01), Hoda et al.
Alphonse Fritz
Bushnell , Esq. Robert E.
Samsung Electronics Co,. Ltd.
Saras Steven
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