Raster V-size adjustment circuit

Details Raster V-size adjustment circuit Raster V-size adjustment circuit

1997-03-31

2001-01-02

Peng, John K. (Department: 2714)

Television

Video display

Cathode-ray tube

C348S746000, C348S747000, C348S380000, C315S008000

Utility Patent

active

06169587

ABSTRACT:

FIELD OF INVENTION
The invention relates to a video display apparatus using a cathode ray tube (CRT), and is particularly concerned with a circuit for adjusting the raster vertical scan size such that a constant raster vertical scan size is substantially maintained.
BACKGROUND OF INVENTION
It is well known that a video display apparatus employing a CRT generates a desired video on the CRT by horizontal and vertical deflection operation of the electron beam selectively impinged on the inner surface of the CRT. In modern digitally controlled CRT-type display apparatus, a microprocessor generates a pulse width modulation (PWM) signal to a digital-to-analog converter (DAC). The control current outputted by the DAC then is inputted to a deflection controller which, in turn, control the vertical scan size of the raster.
In particular, other than expected adjustment instructed by the user of the display apparatus, the vertical scan size of the raster, as well known in the arts, is unexpectedly affected by variation of an external loading, e.g. a variable resistor controlling the brightness of the video displayed on the CRT. The unexpected vertical scan size change, as well known in the arts, is caused by change of high voltage, due to change of the external loading, applied to the anode of the CRT. When the loading becomes heavier, the high voltage to anode can not be maintained at a fixed value. If the high voltage becomes lower, the vertical scan size becomes larger.
In other words, as a critical user adjusts the brightness of the video, unexpected minor change of the raster vertical scan size is perceived by the critical user. Therefore, it is desirable to attain a fixed raster vertical scan size of the video regardless of variation of the brightness.
To overcome the mentioned drawback, one conventional approach utilizing a high voltage regulation loop to maintain a constant high voltage applied to the anode, regardless of change of the external loading, has been implemented. Even though such approach is technically feasible in solving the above-mentioned problem, however, the cost associated with this conventional approach is high. Furthermore, the required physical dimension of the conventional implementation is significant.
The main object of the instant invention is to provide a cost effective alternative to prevent unexpected raster vertical scan size change while a smaller physical dimension is achieved.
A raster vertical scan size adjustment circuit is provided in which a compensated signal, e.g. voltage, responding to variation of the external loading is generated.
SUMMARY OF INVENTION
A raster vertical scan size adjustment circuit including a compensation circuit and a raster vertical scan size control circuit is provided.
The compensation circuit consists of a filter and a compensation network. The compensation network has an input terminal, adapted to connect a voltage reference terminal of a secondary winding of a flyback transformer (FBT).
The raster vertical scan size control circuit consists of a digital-to-analog converter (DAC) and a deflection controller. The DAC has a first input terminal connected to the output terminal of the compensation network, an output terminal generating a control signal, and a second input terminal receiving a PWM signal generated by a microprocessor. The deflection controller has an input terminal receiving the control signal and an output terminal controlling the raster vertical scan size.


REFERENCES:
patent: 4607288 (1986-08-01), Freyberger
patent: 4870331 (1989-09-01), Heinzerling
patent: 4870490 (1989-09-01), Sekiya et al.
patent: 5619285 (1997-04-01), Koybayashi
patent: 5898467 (1999-04-01), Woo
patent: 6011593 (2000-01-01), Onozawa et al.
patent: 08046808 (1996-02-01), None

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