Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
1997-07-11
2001-01-30
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C348S173000, C348S540000, C348S547000
Reexamination Certificate
active
06181088
ABSTRACT:
CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C §119 from an application filed in the Korean Industrial Property Office on Jul. 11, 1996, and there duly assigned Ser. No. 96-28027 and from an application filed in the Korean Industrial Property Office on Oct. 17, 1996, and there duly assigned Ser. No. 96-46519 by that Office.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display apparatus having a cathode ray tube (CRT), and more particularly to a protection circuit and method for protecting a cathode ray tube driving circuit therein against abnormal frequencies of synchronization signals.
2. Background Art
As is well known, a cathode ray tube display apparatus is used as a peripheral apparatus having such a function that a user can see information displayed on its cathode ray tube screen in a personal computer system. It is also known to mute the first grid of the cathode ray tube during a mode conversion or power-on state to prevent a distorted of the raster as contemplated by U.S. Pat. No. 5,463,289 to Moon J. Song and entitled First Grid Muting Circuit.
Additionally, a cathode ray tube display apparatus has a display function which is operated in a text mode or a graphic mode in accordance with the sort of data for display. Thus, when text data is displayed in the cathode ray tube display apparatus, i.e., in a text mode, the computer transfers the text data to the display apparatus, while outputting horizontal and vertical synchronization signals corresponding to the text mode. On the other hand, when there is a necessity of displaying graphic data, the computer transfers the graphic data to the display apparatus, while outputting horizontal and vertical synchronization signal corresponding to the graphic mode to the display apparatus.
I have found that when the frequencies of the synchronization signals H_SYNC and V_SYNC are changed over limited ranges, in the typical contemporary design, a microcomputer will interrupt generation of horizontal and vertical synchronization signals. The microcomputer however, still permits the synchronization signal generator to provide the horizontal and vertical synchronization signals. If the frequencies of these synchronization signals grossly exceeds the limited ranges within a particular interval, the microcomputer will be unable to immediately interrupt the abnormal frequencies. I have noticed that consequently that the microcomputer will not be able to prevent the generation of these abnormal frequencies until expiration of a predetermined period. This may, unfortunately, results in the cathode ray tube driving circuit being damaged by the abnormal frequencies.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved cathode ray tube driving process and circuit.
It is another object to provide a cathode ray tube apparatus having a protection circuit and method for protecting a cathode ray tube driving circuit from being severely damaged by abnormal high frequencies which are beyond limited ranges.
It is still another object to provide a cathode ray tube display apparatus which can safely drive a cathode ray tube regardless of the frequency changes of the synchronization signals.
According to an aspect of the present invention, a cathode ray tube display apparatus having a cathode ray tube, and a cathode ray tube driving circuit which drives the cathode ray tube in response to a synchronization signal provided from a host, comprises: a state signal generating circuit for receiving the synchronization signal to generate a state signal indicating when a frequency of the synchronization signal is changed; and a protection circuit for cutting off supply of the synchronization signal to the cathode ray tube driving circuit in response to the state signal for preventing the cathode ray tube driving circuit from being damaged in response to a change in frequency of the synchronization signal.
In an embodiment of this aspect, the state signal generating circuit generates the state signal when the frequency of the synchronization signal exceeds a limited range. The synchronization signal is either a horizontal or vertical synchronization signal. The protection circuit comprises a switch driving section for generating a switch driving signal in response to the state signal; and a switch section responsive to the switch driving signal, for connecting the synchronization signal received from the state signal generating circuit to a grounding terminal. Also, the cathode ray tube device further comprises a microcomputer, wherein the microcomputer receives the synchronization signal provided from the host and supplies the received synchronization signal to the state signal generating circuit.
According to another aspect of the present invention, a cathode ray tube display apparatus having a cathode ray tube, and a cathode ray tube driving circuit which drives the cathode ray tube in accordance with a synchronization signal provided from a host, comprises: a microcomputer for receiving the synchronization signal provided from the host; a state signal generating circuit for receiving the synchronization signal from microcomputer, and when a frequency of the synchronization signal is changed, for generating a state signal which indicates when the frequency of the synchronization signal exceeds a limited range; a switch driving circuit for generating a switch driving signal in response to the state signal; and a switch circuit responsive to the switch driving signal, for connecting the synchronization signal from state signal generating circuit to a ground terminal, such that the switch driving circuit and the switch circuit prevent the cathode ray tube driving circuit from getting damaged when a change in the frequency of the synchronization signal is excessive.
In an embodiment of this aspect, the synchronization signal is either a horizontal or vertical synchronization signal.
REFERENCES:
patent: 4459517 (1984-07-01), Hicks
patent: 4654717 (1987-03-01), Stoughton
patent: 4820959 (1989-04-01), Griffey
patent: 5089754 (1992-02-01), George
patent: 5463289 (1995-10-01), Song
patent: 5491794 (1996-02-01), Wu
patent: 5502502 (1996-03-01), Gaskill et al.
patent: 5555032 (1996-09-01), Kung
patent: 5671017 (1997-09-01), Chujo
Bushnell , Esq. Robert E.
Philogene Haissa
Samsung Electronics Co,. Ltd.
Tran Thuy Vinh
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