Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Patent
1986-01-28
1987-07-21
Blum, Theodore M.
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
358174, 358177, H02J 2970, H04N 552
Patent
active
046820876
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an apparatus for controlling an amplitude of a vertical deflection signal which is applied to control the amplitude of the vertical deflection signal of a television receiver.
BACKGROUND ART
Recently, television receivers are also used as output display sections of microcomputer apparatuses. However, the vertical frequency of an output video signal which is outputted from the microcomputer apparatus is determined from the number of characters in one line or the like and is not limited to the standard frequency of 60 Hz but differs within a range of, for example, 50 to 60 Hz.
In the case of supplying such a video signal to the television receiver, there occur the problems such as inferior vertical linearity, inferior horizontal pin distortion, vertical pull-out, overamplitude of or lack of amplitude of vertical deflection, and the like.
For example, assuming that the frequency of a vertical sync signal V.sub.sy shown in FIG. 5A increased as shown by broken lines than that represented by a solid line, the amplitude of the vertical deflection signal decreases as shown by a broken line in FIG. 5B. Thus, the vertical deflection amplitude lacks.
There has conventionally been known the method whereby the change in vertical amplitude due to the difference in vertical frequency between the NTSC and CCIR systems is corrected by switching the value of the circuit element by a manual switch. However, according to this constitution, it is necessary to operate the manual switch and the vertical amplitude cannot be automatically corrected, so that it is improper for correction of the vertical amplitude when the output video signal of the microcomputer apparatus is displayed.
To automatically correct the vertical amplitude, it is necessary to detect the variation in vertical amplitude corresponding to the vertical frequency of the input signal. As an example of detection of the change of the vertical frequency, there has been known the method whereby a monostable multivibrator is triggered by a vertical sync signal and its output signal is integrated and the vertical frequency is determined from the level of the integrated output. However, since the vertical frequency is fairly low, the value of the capacitor for integration is large and there is a drawback such that response speed is low when the vertical frequency changes.
DISCLOSURE OF INVENTION
It is therefore an object of the present invention to provide an apparatus for controlling an amplitude of a vertical deflection signal in which a response speed is high and there is no need to largely change the existing circuit.
This invention relates to an apparatus for controlling an amplitude of a vertical deflection signal comprising: a level discriminating circuit to discriminate that an amplitude of a sawtooth voltage of a vertical period lies within a range of an almost proper level; a counter whose counting operation is designated so as to either increase or decrease in response to an output signal of the level discriminating circuit and which counts a vertical sync signal on the basis of the output of the level discriminating circuit when the amplitude of the sawtooth voltage of the vertical period is out of the range of the almost proper level; and a D/A converter to convert an output of the counter into an analog detection signal.
According to the invention, the vertical amplitude can be detected at a good response speed, different from the conventional method whereby the monostable multivibrator is triggered by the vertical sync signal and its output is integrated. Therefore, it is possible to prevent the influence on the video interval by the fluctuation in vertical synchronization when the input video signal is switched.
This invention also has advantages such that there is no need to newly constitute the whole system as in the digital television receiver and there is no need to largely change the existing circuit.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram of an embodiment of the present in
REFERENCES:
patent: 3070756 (1962-12-01), Fischman
patent: 3970894 (1976-07-01), Yasuda et al.
patent: 3979683 (1976-09-01), Ikeda
patent: 4104567 (1978-08-01), Peer et al.
patent: 4323923 (1982-04-01), Reneau
Blum Theodore M.
Cain David
Sony Corporation
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