AFC System for a synthesizer tuning system
First Claim
1. An AFC system for a synthesizer-tuned television receiver comprising:
- voltage-controllable reference oscillator;
p1 voltage applying means coupled between the tuning control terminal of reference oscillator and between at least a first and a second source of tuning voltage, and a means for selecting the source of tuning voltage applied to the tuning control terminal;
a crystal-controlled oscillator;
a control circuit having an input coupled to the crystal-controlled oscillator and an output coupled to the reference oscillator;
an AFC switch coupled to the control circuit, the AFC switch having an OFF condition and an ON condition whereby when the AFC switch is in the OFF condition the reference oscillator is continuously coupled by the control circuit to the crystal-controlled oscillator so that the reference oscillator is injection locked to the crystal-controlled oscillator and frequency of its output signal is equal to the frequency of the crystal-controlled oscillator; and
an acquisition delay circuit having an input coupled to the voltage applying means and an output coupled to the control circuit so that when a source of tuning voltage is selected the reference oscillator is, for a period of time determined by the acquisition delay circuit, injection locked to the crystal-controlled oscillator and subsequently controlled by the voltage applied to the tuning control terminal through the voltage applying means.
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Accused Products
Abstract
A voltage-controllable reference oscillator for a synthesized receiver. In one mode of operation the reference oscillator is injection locked to a crystal-controlled oscillator so that the receiver'"'"'s local oscillator frequency is a rational multiple of the crystal oscillator frequency. In another mode of operation the reference oscillator is isolated from the crystal-controlled oscillator and its operating frequency is determined by the voltage applied at its tuning control terminal. The control voltage is selectively provided by a manually variable fine tuning circuit or by an AFC circuit. An acquisition delay circuit develops a pulse when a channel is selected or when the source of tuning voltage is changed, thereby assuring that the reference oscillator is operating in the injection-locked mode until the synthesizer phase-locked loop has achieved acquisition.
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Citations
16 Claims
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1. An AFC system for a synthesizer-tuned television receiver comprising:
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voltage-controllable reference oscillator;
p1 voltage applying means coupled between the tuning control terminal of reference oscillator and between at least a first and a second source of tuning voltage, and a means for selecting the source of tuning voltage applied to the tuning control terminal;a crystal-controlled oscillator; a control circuit having an input coupled to the crystal-controlled oscillator and an output coupled to the reference oscillator; an AFC switch coupled to the control circuit, the AFC switch having an OFF condition and an ON condition whereby when the AFC switch is in the OFF condition the reference oscillator is continuously coupled by the control circuit to the crystal-controlled oscillator so that the reference oscillator is injection locked to the crystal-controlled oscillator and frequency of its output signal is equal to the frequency of the crystal-controlled oscillator; and an acquisition delay circuit having an input coupled to the voltage applying means and an output coupled to the control circuit so that when a source of tuning voltage is selected the reference oscillator is, for a period of time determined by the acquisition delay circuit, injection locked to the crystal-controlled oscillator and subsequently controlled by the voltage applied to the tuning control terminal through the voltage applying means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A reference oscillator for a frequency synthesizer, said oscillator comprising:
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a crystal-controlled oscillator; a voltage-controllable oscillator selectively coupled to the crystal-controlled oscillator and having a voltage control terminal at which is applied a voltage for determining the natural frequency of operation of the voltage controllable oscillator; first switching means having a pole coupled to the voltage control terminal; a fine tuning circuit coupled to one terminal of the first switching means; an AFC control circuit coupled to another terminal of the first switching means; a control circuit having an input coupled to the crystal-controlled oscillator and an output coupled to the voltage-controllable oscillator; second switching means having a pole coupled to the control circuit and a first terminal corresponding to an AFC OFF condition and a second terminal corresponding to an AFC ON condition so that when the second switching means is in the AFC OFF condition the voltage-controllable oscillator is injection locked to the crystal controlled oscillator and when the second switching means is in the AFC ON condition the operating frequency of the reference oscillator is determined by the voltage applied to the voltage control terminal of the voltage-controllable oscillator. - View Dependent Claims (16)
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Specification