Television – Television transmitter circuitry – Modulator
Reexamination Certificate
2005-09-06
2005-09-06
Srivastava, Vivek (Department: 2611)
Television
Television transmitter circuitry
Modulator
C348S532000, C348S678000
Reexamination Certificate
active
06940561
ABSTRACT:
The depth of modulation and the absolute RF carrier level of an amplitude-modulated video signal are automatically adjusted. For adjustment of the depth of modulation, a sync tip of the video signal is sampled, corrected and normalized to a reference level, e.g., a 50% video level. A reference pulse is inserted into the video signal, e.g., in a sync pulse or in lines22and/or23of the vertical blanking interval. The reference pulse is sampled and compared to the normalized sync tip pulse to determine an error. The error is converted to an adjustment signal for a charge pump which increases or decreases the depth of modulation accordingly. For adjustment of the absolute carrier level, the insertion of a reference pulse is not required. Instead, a reference value is stored in a memory and retrieved for comparison with the corrected sync tip pulse. An error term is computed and converted to an adjustment signal for a charge pump which increases or decreases the absolute carrier level accordingly. Several modulation circuits can share a common microprocessor controller.
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Glaab Joseph B.
Stufflet Alfred W.
Cullen Lawrence T.
General Instrument Corporation
Srivastava Vivek
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