Phase locked loop angle modulation system with large modulation index

• US 4,009,455 A
• Filed: 09/11/1975
• Issued: 02/22/1977
• Est. Priority Date: 09/12/1974
• Status: Expired due to Term

• Current Assignee: Victor Company of Japan Limited (JVC Kenwood Corporation), Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Victor Company of Japan Limited (JVC Kenwood Corporation), Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Ishigaki, Yukinobu, Fukui, Kiyotake
• Primary Examiner(s): Grimm, Siegfried H.
• Application Number:
  US05/612,297
• Time in Patent Office: 530 Days
• Field of Search: 332/16 R, 332/16 T, 332/18, 332/19, 332/30 V, 331/17, 331/23, 325/45, 325/145, 325/148
• US Class Current: 332/127
• CPC Class Codes: H03C 3/095 applying frequency modulation to the loop in front of the voltage controlled oscillator

Abstract

An angle modulation system comprises a voltage controlled oscillator, and at least one frequency divider for dividing the frequency of the output of the voltage controlled oscillator. A phase comparator responds to the output of the frequency divider and to a reference signal supplied from a reference signal oscillator, through another frequency divider. A frequency selection circuit is provided in the path extending from the output side of the voltage controlled oscillator, through the frequency divider, to the phase comparator. This selection circuit eliminates an undesired side band component in the output of the voltage controlled oscillator and derives a required carrier component. An adder adds an input modulation signal and the output of the phase comparator, and applies the resulting signal to the voltage controlled oscillator. From the output of the voltage controlled oscillator, an angle-modulated wave signal is derived with a large signal to noise ratio and large modulation index.

Claims

1. An angle modulation system comprising:

means for supplying a modulating signal;

a voltage controlled oscillator means operating at an oscillation frequency controlled by an applied signal, said voltage controlled oscillator naturally having an undesired side band;

frequency dividing means for dividing the output frequency of the voltage controlled oscillator with a specific frequency dividing ratio;

means for supplying a reference signal of a specific frequency;

phase comparison means jointly responsive to the output of the frequency dividing means and the reference signal from the reference signal supplying means;

frequency selection means in a path extending from the voltage controlled oscillator means, through the frequency dividing means, to the phase comparison means, said frequency selection means eliminating said undesired side band component from the output of the voltage controlled oscillator means;

adding means for adding the modulating signal and the output signal of the phase comparison means, and for applying the resulting signal to the voltage controlled oscillator means;

carrier elimination means in a path extending from the phase comparison means to the adding means for eliminating a frequency divided carrier component; and

means for deriving an angle-modulated signal from the output of the voltage controlled oscillator.

2. An angle modulation system as claimed in claim 1 in which said frequency selection means comprises a band-pass filter circuit and an amplifying and waveform shaping circuit.

3. An angle modulation system as claimed in claim 1 in which said frequency dividing means comprises a first frequency divider means for dividing the output of the voltage controlled oscillator with a first frequency dividing ratio, and a second frequency divider means for dividing the output of the first frequency divider with a second frequency dividing ratio, said frequency selection means being coupled between the first and second frequency dividers, said reference signal supplying means comprises a reference oscillator means for producing a reference frequency, and a third frequency divider means for dividing the reference frequency into a frequency which is substantially equal to the output signal of the second frequency dividing means.

4. An angle modulation system comprising:

means for supplying a modulating signal;

a voltage controlled oscillator means for generating an output frequency controlled by an applied signal, said oscillator output naturally containing an unwanted side band component;

a first frequency divider means for dividing the output of the voltage controlled oscillator with a first frequency dividing ratio;

frequency selection means for eliminating said undesired side band component from the output of the first frequency divider;

a second frequency divider means for dividing the output of the frequency selection means with a second frequency dividing ratio;

a reference oscillator means for producing a reference frequency;

a third frequency divider means for dividing the output reference frequency into a frequency which is substantially equal to the output signal of the second frequency divider;

phase comparison means supplied with the output of the second frequency divider means and the output of the third frequency divider means;

a loop filter means for eliminating a high frequency component in the output of the phase comparison means;

carrier elimination means for eliminating a frequency divided carrier component in the output of the loop filter;

adding means for adding the modulating signal and the output signal for the carrier elimination means, and for applying the resulting signal to the voltage controlled oscillator; and

means for deriving an angle-modulated signal from the output of the voltage controlled oscillator.

5. An angle modulation system comprising:

means for supplying a modulating signal;

a voltage controlled oscillator means operating at an output frequency which is controlled by an applied signal, said output naturally including a side band which is undesired in the angle modulation system;

frequency dividing means for dividing the output frequency of the voltage controlled oscillator with a specific frequency dividing ratio;

means for supplying a reference signal of a specific frequency;

phase comparison means responsive to the output of the frequency dividing means and the reference signal from the reference signal supplying means;

frequency selection means in a path extending from the voltage controlled oscillator means, through the frequency dividing means, to the phase comparison means, said frequency selection means eliminating said undesired side band component in the output of the voltage controlled oscillator;

adding means for adding the modulating signal and the output signal of the phase comparison means, and for applying the resulting signal to the voltage controlled oscillator;

means for deriving an angle-modulating signal from the output of the voltage controlled oscillator means;

means for demodulating an angle-modulated wave signal from the voltage controlled oscillator means;

means for inverting the polarity of an input signal supplied to the voltage controlled oscillator means and for mixing the same with the output of the demodulation means and deriving a noise signal component; and

means for inverting the polarity of the derived noise signal component, mixing the same with the output of the adding means and applying the resulting signal to the voltage controlled oscillator.

6. An angle modulation system comprising:

means for supplying a modulating signal;

a voltage controlled oscillator means for generating an output frequency controlled by an applied signal, said output signals including an undesired frequency band;

frequency dividing means for dividing the output frequency of the voltage controlled oscillator with a specific frequency dividing ratio;

means for supplying a reference signal of a specific frequency;

phase comparison means responsive to the output of the frequency dividing means and the reference signal from the reference signal supplying means;

frequency selection means in a path extending from the voltage controlled oscillator means, through the frequency dividing means, to the phase comparison means, said frequency selection means eliminating said undesired frequency band from the output of the voltage controlled oscillator;

adding means for adding the modulating signal and the output signal of the phase comparison means, and for applying the resulting signal to the voltage controlled oscillator;

means for deriving an angle-modulated signal from the output of the voltage controlled oscillator means;

a loop filter means in a path extending from the phase comparison means to the adding means for eliminating a high frequency component in the output of the phase comparison means, said loop filter means comprising an amplifier and a feedback loop for the amplifier, said loop filter means having a relatively large time constant determined by said feedback loop;

a phase locked loop including the voltage controlled oscillator means, the frequency dividing means, the frequency selection means, the phase comparison means, and the adding means;

means for grounding the feedback loop in the loop filter means during a short time period after power is turned on; and

Dc limiting means for producing a DC voltage during at least the time period after the power is turned on and before the instant when the phase locked loop is pulled into synchronism, said DC limiting means being in a path extending from the phase comparator, and through the loop filter, to the adding means.