Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
1999-02-08
2001-03-27
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S370000, C315S408000
Reexamination Certificate
active
06208093
ABSTRACT:
The invention relates to a dynamic clamping arrangement of a deflection circuit.
A television receiver, computer or monitor may have the capability of selectively displaying picture information in the same color cathode ray tube (CRT) using a deflection current at different horizontal scan frequencies. Typically, an S-capacitor is coupled to a horizontal deflection winding of a horizontal deflection circuit output stage to correct a deflection related beam landing error referred to as S correction.
A horizontal rate synchronizing signal that controls the horizontal deflection circuit may be subject to an abrupt phase change in a horizontal period that occurs, during the vertical blanking interval. Such abrupt phase change may be, for example, deliberately introduced to thwart unauthorized video recording of the video signal. Consequently, the stored energy in an inductance coupled to the supply voltage of the horizontal deflection circuit output stage may temporarily increase.
The increased stored energy is subsequently dissipated. However, disadvantageously, the return to steady state operation may be accompanied with ringing in currents and voltages produced in the horizontal deflection circuit output stage. A resistor-capacitor-diode (RCD) clamp coupled across the S-capacitance has been used to reduce such ringing by forcing the horizontal deflection circuit output stage to operate near critical damping.
When displaying the picture information of a television signal defined according to a broadcasting standard, it may be more economical to utilize a horizontal deflection current at a rate of approximately 16 KHz, referred to as the 1f
H
rate. Whereas, when displaying the picture information of a high definition television signal or a display monitor data signal, the rate of the horizontal deflection current may be equal to or greater than 32 KHz, referred to as 2nf
H
. The value n is equal to or greater than 1.
In a horizontal deflection circuit output stage of a video display monitor capable of operating at multi-scan rates, it is known to vary the number of in-circuit S-capacitors using switched S-capacitors. The selection of the S-capacitors is made via selectable switches, in accordance with the selected horizontal deflection frequency.
In a TV receiver-monitor, which operates at the different horizontal scanning frequencies, a single RCD clamp may not be able to provide the required damping for the entire range of the horizontal scanning frequency. It may be desirable to provide the required damping for the entire frequency range.
In carrying out an inventive feature, the number of in-circuit RCD clamps varies using switched RCD clamps. The selection of the RCD clamps is made via a selectable switch, in accordance with the selected horizontal deflection frequency.
A video display deflection apparatus operating at multi-scan horizontal frequencies, embodying an inventive feature, includes a source of an input signal at a frequency related to a selected horizontal deflection frequency. A first switch, responsive to the first input signal and coupled to a horizontal deflection winding and to a retrace capacitance, is used for generating a horizontal deflection current in the horizontal deflection winding at the selected horizontal deflection frequency. The horizontal deflection winding is coupled to an S-shaping capacitance for generating an S-shaping voltage that provides horizontal linearity distortion correction. A pair of clamp circuits is selectable in accordance with the selected horizontal deflection frequency for clamping the S-shaping voltage, during a portion of a horizontal period. A second switch is responsive to the input signal and coupled to one of the clamp circuits for selecting the one clamp circuit, when the selected horizontal deflection frequency is within a first range, and for de-selecting the one clamp circuit, when the selected horizontal deflection frequency is within a second range.
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United States Patent Appln 09/130820 filed Aug. 7, 1998 (RCA 89042).
Fried Harvey D.
Henig Sammy S.
Nguyen Hoang
Philogene Haissa
Thomson Licensing S.A.
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