Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Patent
1989-10-27
1990-09-11
Issing, Gregory C.
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
315387, 315395, H01J 2956, H01J 2970, H01J 2972
Patent
active
049565850
DESCRIPTION:
BRIEF SUMMARY
The invention relates to the field of deflection circuits for picture tubes, and in particular, to deflection circuits for generating symmetric deflection currents.
In a conventional line deflection circuit for a picture tube, for example in a television receiver or a monitor, the electron beam is deflected from the left edge of the picture to the right during the forward trace sweep time of a line. The forward trace is followed by a retrace interval during which the electron beam returns to the left edge of the picture at high speed. The rapid change of the deflecting current during the retrace interval creates a relatively high voltage peak at the horizontal scan output transistor and the line sweeping or deflection coil. The voltage peak must be taken into consideration in choosing the capacity of these parts.
Television systems with enhanced resolution, for example in high definition television (HDTV), have an increased number of scan lines and correspondingly reduced line duration. The demands of more scan lines and faster line scanning can cause problems. These problems include: a need for increased performance, for example switching speed; a higher retrace voltage at the horizontal scan output transistor and at the line sweeping or deflection coil; and, increased sweep radiation.
It is known (IEEE Transactions on Consumer Electronics, Vol. CE-31, No. 3, Aug. 1985, pages 255 through 261) to operate in such systems with enhanced resolution by means of bidirectional, for example symmetrical, line deflection. During bidirectional line deflection, the electron beam for writing a line is deflected from the left edge of the picture to the right, and subsequently, without retracing, deflected from the right edge of the picture to the left edge, for writing the next line at the same speed. Thus, the rapid retrace of the prior art, from the right edge of the picture to the left, and the consequent problems resulting from the fast change of the deflecting current do not occur. Bidirectional deflection is also advantageous in that the power loss and the sweep radiation of the line deflecting circuit are reduced. In a symmetrical deflection circuit, for example, the deflection current has a triangular shaped waveform, which changes from a negative value to a positive value during one line and from the positive value to the negative value during the following line. The deflecting current can, in an approximation to a triangular shaped waveform, be a sinusoidal waveform. In the triangular waveform, as well as in the sinusoidal waveform, the peaks of the deflection current always occur between successive scan lines, beyond the boundaries of the screen, whereas the zero crossings of the deflection current occur at the center of each scan line.
A deflection current with a triangular shaped waveform may be obtained by applying a square wave shaped voltage waveform of half the line frequency to the deflection coil via a suitable circuit. Ideally, the square wave shaped voltage generates a triangular shaped current in the deflection coil. The positive voltage portion of the square wave produces the positive sloped portion of the triangular waveform, whereas the negative voltage portion of the square wave produces the negative sloped portion of the triangular waveform. The zero crossing of the deflecting current is always located in the line center and the deflecting current runs in a symmetrical way, with reversed sign in both halves of the line forward trace sweep time before and after the zero crossing.
The deflection current is subject to ohmic resistance, particularly for example, the inevitable ohmic resistance of the deflection coil. Accordingly, the desired waveform shape of the ideal deflecting current is not always achieved in practice. As a result, the zero crossing of the deflecting current during a line may not be in the center of the line, and the halves of each waveform during each period may be curved differently, that is, not symmetric. Thus, errors in the pattern and the luminance of the picture shown a
REFERENCES:
patent: 4672449 (1987-06-01), Kraus et al.
patent: 4680599 (1987-07-01), Wertz et al.
Symmetric Line Deflection for Colour TV Receivers with Enhanced Picture Quality, Une E. Kraus, IEEE Transactions, vol. CE31, No. 3, Aug. 1985, pp. 255-261.
Deutsche Thomson-Brandt GmbH
Fried Harvey D.
Issing Gregory C.
Laks Joseph J.
Tripoli Joseph S.
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