Television – Image signal processing circuitry specific to television – Transition or edge sharpeners
Reexamination Certificate
1999-05-26
2001-09-25
Kostak, Victor R. (Department: 2711)
Television
Image signal processing circuitry specific to television
Transition or edge sharpeners
C348S625000
Reexamination Certificate
active
06295097
ABSTRACT:
The invention relates to adjusting beam scanning velocity to improve sharpness in a raster scanning display such as a cathode ray tube (CRT) display.
BACKGROUND
The sharpness of a video display may be improved by varying the horizontal scanning rate of the beam in response to variations of the luminance component of the video signal. The luminance signal is differentiated and the differentiated luminance signal is used to generate a current for driving an auxiliary beam deflection element, for example, a scan velocity modulation (SVM) coil to modify the horizontal scanning rate so as to emphasize contrast between light and dark areas of the display. For example, at a transition from black to white in a given horizontal scan line, the beam scanning speed is increased approaching the transition, thus making the display relatively darker in the black area of the transition. Upon passing the transition into the white area, the beam speed is decreased such that the beam dwells relatively longer, making the display relatively brighter. The reverse occurs in passing from light to dark.
The SVM coil operates to add or subtract from the magnetic horizontal beam deflection field applied by the main horizontal deflection coils. The angle of beam deflection is a function of horizontal rate scanning current, generally a sawtooth current. The horizontal rate scanning current causes the beam to sweep across a horizontal raster line at a vertical position determined by a vertical rate sawtooth current, coupled to the vertical deflection coils.
The sawtooth scanning drive currents are adjusted to account for the fact that the display screen is substantially flat rather than spherical. A given amount of angular beam deflection produces a smaller linear horizontal displacement of the beam at the center of the flat screen and a greater amount at the edges of the screen, because the screen is relatively farther from the source of the beam when scanning at the edges of the screen than at the center of the screen.
SUMMARY
In an arrangement embodying an inventive feature, each of a horizontal rate correction signal and a vertical rate correction signal is produced in a waveform generator that includes a counter. The correction signals are combined to form a combined, SVM control signal that is coupled to a limiter. The combined, SVM control signal varies in accordance with the variation of the beam spot in each of the vertical and horizontal directions. The limiter produces a piece-wise linearized signal that is coupled to a modulator circuit. The modulator circuit is also responsive to a video signal. The modulator modulates, in accordance with the limiter output signal, a signal produced by forming a time-derivative of the video signal. The modulator output signal is coupled to an amplifier that drives an SVM winding. The use of the limiter, advantageously, simplifies the generation of the piecewise linearized signal.
In accordance with an inventive feature, a first signal that varies in accordance with a position of an electron beam is provided. A limiter is responsive to the first signal for generating a second signal having a limited, piece-wise linearized first portion, when the first signal is outside a range of values. The second signal has a second portion that varies, when the first signal varies within the range of values. A correction signal is generated from the second signal and from a video signal. The correction signal is coupled to a deflection winding to produce scan velocity modulated deflection of the electron beam.
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Fried Harvey D.
Henig Sammy S.
Kostak Victor R.
Thomson Licensing S.A.
Tripoli Joseph S.
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