Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
1999-11-05
2001-05-29
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C348S626000
Reexamination Certificate
active
06239561
ABSTRACT:
BACKGROUND OF THE INVENTION
The apparent sharpness of a cathode ray tube picture may be enhanced by modulation of the scanning beam velocity in accordance with a derivative of the display picture video signal. The derivative signal, or SVM signal, may be derived from a luminance component of the video display signal and is employed to produce scanning beam velocity variations. Slowing the scanning velocity of the electron beam results in a localized brightening of the displayed image, whereas acceleration of the scanning velocity results in a localized darkening of the display. Thus, edges of the displayed image may be perceived to have a more rapid transition or faster rise time by varying the intensity of the display about the edge. This method of sharpness enhancement provides various advantages over that provided by video frequency response peaking, for example, blooming of peaked high luminance picture elements is avoided, and in addition, unwanted video noise occurring within the bandwidth of the video peaking arrangement is not enhanced.
The velocity of the scanning beam may be modulated by an SVM coil, positioned on the CRT neck to generate a supplementary or SVM deflection field. The SVM field, in conjunction with the main deflection field, produces electron beam acceleration or deceleration responsive to the polarity of current in the SVM coil. Thus the amount of beam acceleration or deceleration is proportional to the magnitude of the SVM current, which in turn is proportional to components of the displayed image signal.
Since the SVM signal is generally representative of the high frequency content of the display video signal, it can be appreciated that the SVM coil current is of sufficient magnitude and spectral composition to be readily coupled to yield unwanted, extraneous crosstalk components. Furthermore, any unwanted non-linear processing of the SVM signal will generate harmonically related spectral artifacts which are readily coupled via various crosstalk mechanisms.
SUMMARY OF THE INVENTION
An apparatus for image enhancement in a cathode ray tube display comprises an amplifier for a scanning velocity modulating signal. The scanning velocity modulating signal has an AC component and a DC value. A feedback circuit is responsive to power dissipation in the amplifier for controlling the AC component and the DC value with a first control signal, and controlling only the DC value with a second control signal.
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Clinger James
Davenport Francis A.
Fried Harvey D.
Thomson Licensing S.A.
Tripoli Joesph S.
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