General Instrument Corporation

Other

General Instrument Corporation of Delaware

Alfred W Stufflet

Kevin T Chang

Joseph B Glaab

Kevin Chang

Timothy D Rea

Richard W Westerfer

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 linesand/orof 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.

Automatic modulation and RF carrier level control of sync suppressed television signals

A method and device for scrambling video signals for broadcast in a proprietary television system includes modifying the vertical or horizontal synchronization pulses of the video signal to prevent unauthorized viewers from properly displaying the programming content. Preferably, the vertical sync pulses are removed from the signal prior to broadcast and replaced with horizontal sync pulses. A descrambler used with the receiving television uses the manner in which the false horizontal sync pulses were inserted into the video signal to recreate a sufficient approximation of the vertical sync pulses.

Method and apparatus for television signal scrambling using vertical sync replacement

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 lines,and/or,of 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.

Automatic modulation control of sync suppressed television signals

A signal such as an analog scrambled television signal in a cable television network has first scrambling mode data which is compatible with a first decoder population, but not a second decoder population. The scrambled television signal is processed to determine the scrambling mode without recovering the first scrambling mode data. Second scrambling mode data which is compatible with the second decoder population is then provided in the scrambled television signal, for example, in the vertical blanking interval or on an audio subcarrier. During processing to determine the scrambling mode, the television signal is delayed, e.g., by digitizing it and temporarily storing it in memory. The delay compensates for the time required to determine the scrambling mode. The television signal is recovered in the analog domain prior to inserting the second scrambling mode data. The system is compatible with various scrambling modes, including sync suppression and inversion of the active video as well as with dynamic scrambling mode changes.

Determination of scrambling mode of a television signal

A method and apparatus for preventing unauthorized descrambling of cable programming includes selective relocation of the service data channel within the vertical blanking interval thereby preventing unauthorized descrambling of programming by conventional descramblers.

Dynamic relocation of the service data channel

A video signal is modified to include a supplemental burst signal on at least some of the scan lines for each frame. The supplemental burst signals are used to prevent a pirate decoder from descrambling horizontally sync suppressed scrambled signals by deriving a synchronization timing reference from the color burst signal. The supplemental burst signals can also or alternatively be used to carry data in an otherwise conventional analog video signal.

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Norristown, PA, United States of America

Alfred W Stufflet