Digital frequency lock tuning system

• US 4,476,584 A
• Filed: 02/08/1979
• Issued: 10/09/1984
• Est. Priority Date: 02/08/1979
• Status: Expired

• Current Assignee: General Instrument Corporation (CommScope Holding Company, Inc.)
• Original Assignee: Jerrold Electronics Corp. (CommScope Holding Company, Inc.)
• Inventors: Dages, Charles L.
• Primary Examiner(s): NG, JIN FAY
• Application Number:
  US06/010,408
• Time in Patent Office: 2,070 Days
• Field of Search: 358/191.1, 358/195.1, 455/164, 455/182, 455/184-186
• US Class Current: 455/182.1
• CPC Class Codes: H03J 5/0263 the digital values being held in an auxiliary non erasable memory

Abstract

A tuning system for use in radio frequency multi-signal receiving systems, e.g a CATV converter, 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.

Claims

1. A closed loop digital tuning system, the system comprising,

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 oscillation 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 a plurality of address words, each address word representing a particular operating channel in a CATV system,

memory means for storing a plurality of second digital words, each of said second digital words representing any desired frequency of oscillation for said oscillator means,

means responsive to the address words for retrieving from said memory means one of said second digital words, the particular location of said second digital word within said memory means being identified by said address word representing a particular operating channel in said CATV system,

means for storing the second digital word retrieved from said memory means,

comparator means for comparing the values of said first digital word with the value of said stored second digital word, and means responsive to a difference in value between said first digital word and said stored second digital word determined by said comparator means for varying said control voltage for said oscillator means, whereby said actual frequency value is changed to said desired frequency value, wherein there is further included means responsive to fine tuning information for retrieving a third digital word from said memory means, means for adding said third digital word to said second digital word, and means for applying the sum of said second and third digital words to said comparator means.

2. A closed loop digital tuning system, the system comprising,

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 oscillation 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 operating channel in a CATV system,

memory means for storing a plurality of second digital words, each of said second digital words representing any desired frequency of oscillation for said oscillator means,

means responsive to the address words for retrieving from said memory means one of said second digital words, the particular location of said second digital word within said memory means being identified by said address word representing a particular operating channel in said CATV system,

means for storing the second digital word retrieved from said memory means,

comparator means for comparing the values of said first digital word with the value of said stored second digital word, and means responsive to a difference in value between said first digital word and said stored second digital word determined by said comparator means for varying said control voltage for said oscillator means, whereby said actual frequency value is changed to said desired frequency value, wherein said sampling means includes a binary counter for counting cycles of said output oscillation of said oscillator means, and means for applying said oscillation to said binary counter for said predetermined interval of time, wherein said control voltage varying means includes means responsive to the difference in value between said first and second digital words for generating a variable width pulse, the width of said pulse being directly related to the difference in binary value between said first and second digital words, wherein there is further included means for determining the polarity of the difference in value between said first and second digital words, and means responsive to a positive polarity and to said variable width pulse for decreasing the value of said control voltage, wherein there is further included means responsive to fine tuning information for retrieving a third digital word from said memory means, means for adding said third digital word to said second digital word, and means for applying the sum of said second and third digital words to said comparator means.