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US 4,298,988 AGranted
Digital channel selection and fine tuning system
AssigneeJerrold Electronics Corporation
InventorCharles L. Dages
Life of this patent
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Abstract
A tuning system for use in a radio frequency multi-signal receiving system, e.g., for CATV converters, utilizes a closed feedback loop digital arrangement for channel selection (local oscillator frequency control) and channel fine tuning. The system may be implemented either via discrete hardware or through the use of microprocessor controlled apparatus. In accordance with one aspect of the present invention, double heterodyne tuning apparatus automatically compensates for frequency drift in the second local oscillator.
Claims7
A closed loop double heterodyne digital tuning system, the system comprising,
- first local oscillator means responsive to a variable control voltage for generating an oscillation having a frequency dependent on the magnitude of said control voltage,
- sampling means for sampling the actual output frequency of said oscillator means for a predetermined interval of time and for generating a first digital word representing the actual value of said frequency,
- means responsive to incoming channel information for generating a selected one of plurality of address words, each address word representing a particular video operating channel,
- storage means for storing a plurality of second digital words, each of the second digital words representing a desired nominal value of frequency for said oscillator means,
- means responsive to the address words for retrieving from said storage means one of said second digital words, the particular location of said second digital word within said storage means being identified by said address word,
- a second local oscillator,
- second local oscillator drift correcting means including means for sensing the output frequency of said second local oscillator, and means connected to said sensing means for generating a third digital word representative of the frequency variation of said second local oscillator,
- means for combining said third digital word with the second digital word retrieved from said storage means and for storing the results of such combination,
- comparator means for comparing the values of said first digital word with the value of said stored combined second and third digital words, and
- means responsive to a difference in value between said first digital word, and said stored second and third digital words determined by said comparator means for varying said control voltage for said oscillator means, whereby said actual frequency value is changed to the correct frequency value.
7 more elements
A closed loop double heterodyne digital tuning system, the system comprising,
- first local oscillator means responsive to a variable control signal for generating an oscillation having a frequency dependent on the magnitude of said control signal,
- sampling means for sampling the actual output frequency of said oscillator means for a predetermined interval of time and for generating a first signal representing the actual value of said frequency,
- means responsive to incoming channel information for generating a selected one of plurality of address signals, each address signal representing a particular video operating channel,
- storage means for storing a plurality of second signals, each of the second signals representing a desired nominal value of frequency for said oscillator means,
- means responsive to the address signal for retrieving from said storage means one of said second signals, the particular location of said second signal within said storage means being identified by said address signal,
- a second local oscillator,
- second local oscillator drift correcting means including means for sensing the output frequency of said second local oscillator, and means connected to said sensing means for generating a third signal representative of the frequency variation of said second local oscillator,
- means for combining said third signal with the second signal retrieved from said storage means and for storing the results of such combination,
- comparator means for comparing the values of said first signal with the value of said stored combined second and third signals, and
- means responsive to a difference in value between said first signal, and said stored second and third signals determined by said comparator means for varying said control signal for said oscillator means, whereby said actual frequency value is changed to the correct frequency value.
7 more elements
Dependencies are inferred from the claim text.