Circuit for providing accurately spaced video and sound carriers

• US 4,546,387 A
• Filed: 11/04/1982
• Issued: 10/08/1985
• Est. Priority Date: 11/04/1982
• Status: Expired due to Term

• Current Assignee: General Instrument Corporation (CommScope Holding Company, Inc.)
• Original Assignee: General Instrument Corporation (CommScope Holding Company, Inc.)
• Inventors: Glaab, Joseph B.
• Primary Examiner(s): Chin, Tommy P.
• Application Number:
  US06/439,227
• Time in Patent Office: 1,069 Days
• Field of Search: 358/186, 358/197, 358/86, 358/141, 358/143, 358/144, 455/3.4, 455/7, 455/17, 455/102
• US Class Current: 348/724
• CPC Class Codes: H04N 7/06 Systems for the simultaneous transmission of one television signal, i.e. both picture and sound, by more than one carrier H04N7/084, H04N7/087 take precedence

Abstract

A circuit for producing two carrier frequencies (e.g. video and audio) spaced by an accurately controlled, predetermined frequency includes a common reference oscillator connected in two phase-locked loops. Each of the phase-locked loops includes a voltage-controlled oscillator adapted to produce an output signal at one of the carrier frequencies, and a phase detector for comparing a different predetermined fraction of the outputs of the voltage-controlled oscillators in each of the loops with a predetermined fraction of the output frequency of the reference oscillator.

Claims

1. A circuit for producing a modulated audio carrier and a modulated video carrier at accurately spaced first and second respective different frequencies, said circuit comprising a first phase-locked loop for producing said modulated audio carrier signal, a second phase-locked loop for producing a video carrier signal, each of said first and second phase-locked loops including a common reference oscillator, said first phase-locked loop including means for combining an audio carrier signal with an audio input, thereby to form said modulated audio carrier, and further comprising second means for modulating said video carrier signal with a video input, thereby to form said modulated video carrier, and means for operatively combining said modulated audio and video carrier signals to produce a composite television signal including the frequency-spaced modulated audio and video carriers.

2. The circuit of claim 1, in which said first and second phase-locked loops respectively include first and second variable-frequency oscillators for respectively producing said audio and video carrier signals, and first and second comparison means for operatively comparing the frequencies of said first and second variable-frequency oscillators with a predetermined fraction of that of said reference oscillator.

3. The circuit of claim 2, in which said first and second phase-locked loops further comprise first and second frequency-divider means respectively operatively connected between said reference oscillator and said first and second comparison means.

4. The circuit of claim 3, further comprising third and fourth frequency-divider means operatively respectively connected between said first and second variable-frequency oscillators and said first and second comparison means.

5. The circuit of claim 4, in which said first, second, third, and fourth frequency-divider means each have a fixed frequency-division factor.

6. The circuit of claim 5, in which said first and second frequency-divider means respectively operatively connected between said reference oscillator and said first and second comparison means have the same preset division factor.

7. The circuit of claim 6, in which said third and fourth frequency-divider means operatively respectively connected between said first and second variable frequency oscillator and said first and second comparison means have different preset division factors.

8. The circuit of claim 5, in which said third and fourth frequency-divider means operatively connected between said first and second variable-frequency oscillators and said first and second comparison means each includes first and second pairs of series-connected frequency dividers, one of said frequency dividers in each of said divider pairs having a common division factor with a corresponding divider in the other divider pair, the other frequency divider in one of said divider pairs providing a different division factor than the other divider in the other of said divider pairs.

9. A circuit for producing first and second modulated signals spaced by a predetermined frequency from one another within a predetermined tolerance, said circuit comprising a reference oscillator, first and second variable-frequency oscillators respectively nominally adapted to produce output signals at first and second frequencies, first means for operatively comparing a predetermined fraction of the output frequency of said reference oscillator with the output frequency of said first variable-frequency oscillator and for varying the output frequency of said first variable-frequency oscillator in response to the operation of said first comparison means, second comparison means for operatively comparing the output frequency of said reference oscillator and the output frequency of said second variable-frequency oscillator and for varying the output frequency of said second variable-frequency oscillator in response to the operation of said second comparison means and first and second modulating means operatively coupled to said first and second modulated variable-frequency oscillators for providing said first and second modulated signals respectively, whereby the predetermined frequency spacing at said tolerance is maintained between said first and second modulated signals.

10. The circuit of claim 9, further comprising first and second frequency-divider means respectively operatively connected between said reference oscillator and said first and second comparison means.

11. The circuit of claim 10, further comprising third and fourth frequency-divider means respectively operatively connected between said first and second variable-frequency oscillators and said first and second comparsion means.

12. The circuit of claim 11, in which the output frequencies of said first and third frequency-divider means and of said second and fourth frequency-divider means are nominally equal.

13. The circuit of claim 12, in which said first, second, third, and fourth frequency-divider means each have a fixed frequency-division factor.

14. The circuit of claim 13, in which said first and second frequency-divider means respectively operatively connected between said reference oscillator and said first and second comparison means have the same fixed division factor.

15. The circuit of claim 14, in which said third and fourth frequency-divider means operatively respectively connected between said first and second variable frequency oscillators and said first and second comparison means have different preset division factors.

16. The circuit of claim 13, in which said third and fourth frequency-divider means operatively connected between said first and second variable-frequency oscillators and said first and second comparison means each include first and second pairs of series-connected frequency dividers, one of said frequency dividers in each of said divider pairs having a common division factor with a corresponding divider in the other divider pair, the other frequency divider in one of said divider pairs providing a different division factor than the other divider in the other of said divider pairs.

17. A circuit for producing first and second modulated carrier signals having a predetermined frequency spacing from one another at a narrow preset tolerance, said circuit comprising a reference oscillator, a first voltage-controlled oscillator for nominal operation at said first frequency, first and second frequency-divider means respectively operatively connected to said reference oscillator and to said first voltage-controlled oscillator to produce first and second nominally equal comparison frequencies, first phase-detection means operatively connected to the outputs of said first and second frequency divider means for detecting any difference in said first and second comparison frequencies and to produce a first error signal when said first and second comparison frequencies differ from one another, said first error signal being applied to said first voltage-controlled oscillator to vary the frequency thereof;

a second voltage-controlled oscillator for nominal operation at said second carrier frequency, third and fourth frequency-divider means for respectively dividing the frequency of said reference oscillator and said second voltage-controlled oscillator to a second pair of nominally equal comparison frequencies, second phase-detection means for comparing said second pair of comparison frequencies and for producing a second error signal in the event said second pair of compairson frequencies differ from one another, said second error signal being applied to said second voltage-controlled oscillator to vary the frequency thereof, and first and second modulating means operatively coupled to said first and second voltage-controlled oscillators for providing said first and second modulated carrier signals respectively.