A.f.c. circuitry for superheterodyne receivers

Claim 2

In a superheterodyne signal receiver of a type having a tuner including an oscillator, said tuner being adapted to receive input signals having various carrier frequencies and to provide output signals having different carrier frequencies than the carrier frequencies of said input signals and varying over a range including a predetermined frequency, coarse tuning means for varying the frequency of the signal produced by said oscillator to provide a signal which, when heterodyned with one of said input signals, provides a tuner output signal having a carrier frequency within said range, fine tuning means for varying the frequency of the signal produced by said oscillator over a range in which there is provided a signal which, when heterodyned with said one input signal, provides a tuner output signal having a carrier having said predetermined frequency, and automatic frequency control means operable in response to a deviation in the carrier frequency of said output signal of said tuner from said predetermined frequency to automatically vary the frequency of the signal produced by said oscillator in a direction to correct said deviation; the improvement wherein the frequency spectrum within which the carrier frequency of said output signal of said tuner can be varied by said fine tuning means is wholly within the frequency spectrum over which said automatic frequency control means, when abled, is capable of automatically varying the carrier frequency of said output signal of said tuner in a direction to correct a deviation in said carrier frequency of said output signal of said tuner from said predetermined frequency, whereby said fine tuning means is inhibited from mistuning said oscillator to a point at and beyond which said automatic frequency control means, when abled, is ineffective to correct such mistuning.

Claim 3

The invention according to claim 1 wherein said automatic frequency control means includes a device having a characteristic that varies with the magnitude of the voltage applied to said device, said device being connected in circuit with said oscillator as a frequency determining element to vary the frequency of the output signal produced by said oscillator in response to variAtions in the magnitude of said voltage applied to said device, FM discriminator means having an input terminal and an output terminal, and means connecting said output terminal of said discriminator means and said device to apply a voltage to said device that varies in magnitude with the carrier frequencies of signals applied to said input terminal of said discriminator means, said carrier of said signals applied to said input terminal being derived from or being the carrier of said output signal of said tuner, said FM discriminator means being adapted, when said automatic frequency control means is abled, to derive and apply a predetermined DC reference voltage to said device in response to application to said input terminal of a signal having said predetermined carrier frequency and further being adapted to derive and apply DC voltages above and below said reference voltage to said device in response to application to said input terminal of signals having carrier frequencies higher and lower than said predetermined carrier frequency.

Claim 4

The invention according to claim 2 wherein said device is a varactor diode and said characteristic is capacitance.

Claim 5

The invention according to claim 2 including a clipper for limiting the magnitude of said DC voltages to a range that is less than the range of said DC voltages adapted to be applied to said device when said clipper is disabled, said reference voltage being intermediate the upper and lower voltages of said range to which said DC voltages are limited, and means responsive to said coarse tuning means being operated to cause said oscillator to provide a signal having a frequency equal to or above a predetermined oscillator signal frequency for connecting said clipper in circuit with said output terminal and responsive to said coarse tuning means being operated to cause said oscillator to provide a signal having a frequency below said predetermined oscillator signal frequency for disabling said clipper, whereby the pull-in range of said automatic frequency control means is less when said oscillator is providing signals equal to or above said predetermined oscillator signal frequency than it would be when said clipper is disabled.

Claim 6

The invention according to claim 4 wherein said device is a varactor diode and said characteristic is capacitance.

Claim 7

The invention according to claim 5 wherein said superheterodyne signal receiver is a television receiver.

Claim 8

The invention according to claim 6 including a source of DC potential providing a DC voltage equal in magnitude to said predetermined DC reference voltage, means for abling and disabling said automatic frequency control means, and means responsive to disabling of said automatic frequency control means for connecting said source of DC potential and said device to apply said DC voltage of said source to said device.

Claim 9

The invention according to claim 2 wherein said means connecting said output terminal and said device comprise a DC amplifier.

Claim 10

The invention according to claim 8 including a clipper for limiting the magnitude of said DC voltages to a range that is less than the range of said DC voltages adapted to be applied to said device when said clipper is disabled, said reference voltage being intermediate the upper and lower voltages of said range to which said DC voltages are limited, and means responsive to said coarse tuning means being operated to cause said oscillator to provide a signal having a frequency equal to or above a predetermined oscillator signal frequency for connecting said clipper in circuit with said output terminal and responsive to said coarse tuning means being operated to cause said oscillator to provide a signal having a frequency below said predetermined oscillator signal frequency for disabling said clipper, whereby the pull-in range of said automatic frequency control means is less when said oscillator is providing signals equal to or above said predetermined oscillator signal frequency than It would be when said clipper is disabled.

Claim 11

The invention according to claim 9 wherein said device is a varactor diode and said characteristic is capacitance.

Claim 12

The invention according to claim 10 wherein said superheterodyne signal receiver is a television receiver.

Claim 13

The invention according to claim 11 including a source of DC potential providing a DC voltage equal in magnitude to said predetermined DC reference voltage, means for abling and disabling said automatic frequency control means, and means responsive to disabling of said automatic frequency control means for connecting said source of DC potential and said device to apply said DC voltage of said source to said device.

Claim 14

The invention according to claim 12 wherein said means for connecting said clipper in circuit with said output terminal and for disabling said clipper comprise means connecting said clipper in circuit with said output terminal in response to selection of any one of VHF channels 7 to 13 inclusive and disabling said clipper in response to selection of any one of VHF channels 2 to 6 inclusive.

Claim 15

The invention according to claim 2 wherein said superheterodyne signal receiver is a television receiver.

Claim 16

The invention according to claim 2 including a source of DC potential providing a DC voltage equal in magnitude to said predetermined DC reference voltage, means for abling and disabling said automatic frequency control means, and means responsive to disabling of said automatic frequency control means for connecting said source of DC potential and said device to apply said DC voltage of said source to said device.

Claim 17

In a superheterodyne signal receiver of a type having a tuner including an oscillator, said tuner being adapted to receive input signals having various carrier frequencies and to provide output signals having different carrier frequencies than the carrier frequencies of said input signals and varying over a range including a predetermined frequency, coarse tuning means for varying the frequency of the signal produced by said oscillator to provide a signal which, when heterodyned with one of said input signals, provides a tuner output signal having a carrier frequency within said range, fine tuning means for varying the frequency of the signal produced by said oscillator over a range in which there is provided a signal which, when heterodyned with said one input signal, provides a tuner output signal having a carrier having said predetermined frequency, and automatic frequency control means operable in response to a deviation in the carrier frequency of said output signal of said tuner from said predetermined frequency to automatically vary the frequency of the signal produced by said oscillator in a direction to correct said deviation; the improvement comprising means restricting said fine tuning means to vary the carrier frequency of said output signal of said tuner within a frequency spectrum that is wholly within the frequency spectrum over which said automatic frequency control means, when abled, is capable of automatically varying the carrier frequency of said output signal of said tuner in a direction to correct a deviation in said carrier frequency of said output signal of said tuner from said predetermined frequency, whereby said fine tuning means is inhibited from mistuning said oscillator to a point at and beyond which said automatic frequency control means, when abled, is ineffective to correct such mistuning.

Claim 18

In a superheterodyne signal receiver of a type having a tuner including an oscillator, said tuner being adapted to receive input signals having various carrier frequencies and to provide output signals having different carrier frequencies than the carrier frequencies of said input signals and varying over a range including a predetermined frequency, coarse tuning means for varying the frequency of the signal produced by said oscillator to provide a signal which, when heterodyned with one of said input signals, provides a tuner output signal having a carrier frequency within said range, fine tuning means for varying the frequency of the signal produced by said oscillator over a range in which there is provided a signal which, when heterodyned with said one input signal, provides a tuner output signal having a carrier having said predetermined frequency, and automatic frequency control means operable in response to a deviation in the carrier frequency of said output signal of said tuner from said predetermined frequency to automatically vary the frequency of the signal produced by said oscillator in a direction to correct said deviation; the improvement comprising means restricting said fine tuning means to vary the carrier frequency of said output signal of said tuner within a frequency spectrum that is wholly within the frequency spectrum over which said automatic frequency control means, when abled, is capable of automatically varying the carrier frequency of said output signal of said tuner in a direction to correct a deviation in said carrier frequency of said output signal of said tuner from said predetermined frequency, whereby said fine tuning means is inhibited from mistuning said oscillator to a point at and beyond which said automatic frequency control means, when abled, is ineffective to correct such mistuning.

Claim 19

The invention according to claim 16 wherein said automatic frequency control means includes FM discriminator means having an input terminal and an output terminal, a device having a characteristic that varies with the magnitude of the voltage applied to said device, said device being connected in circuit with said oscillator as a frequency determining element to vary the frequency of the output signal produced by said oscillator in response to variations in the magnitude of saId voltage applied to said device, and means connecting said output terminal of said discriminator and said device to apply a voltage to said device that varies in magnitude with the carrier frequencies of signals applied to said input terminal of said discriminator, said carrier of said signals applied to said input terminal being derived from or being the carrier of said output signal of said tuner, said FM discriminator means being adapted, when said automatic frequency control means is abled, to derive and apply a predetermined DC reference voltage to said device in response to application to said input terminal of a signal having said predetermined carrier frequency and further being adapted to derive and apply DC voltages above and below said reference voltage to said device in response to application to said input terminal of signals having carrier frequencies higher and lower than said predetermined carrier frequency.

Claim 20

The invention according to claim 17 including a clipper for limiting the magnitude of said DC voltages to a range that is less than the range of said DC voltages adapted to be applied to said device when said clipper is disabled, said reference voltage being intermediate the upper and lower voltages of said range to which said DC voltages are limited, and means responsive to said coarse tuning means being operated to cause said oscillator to provide a signal having a frequency equal to or above a predetermined oscillator signal frequency for connecting said clipper in circuit with said output terminal and responsive to said coarse tuning means being operated to cause said oscillator to provide a signal having a frequency below said predetermined oscillator signal frequency for disabling said clipper, whereby the pull-in range of said automatic frequency control means is less when said oscillator is providing signals equal to or above said predetermined oscillator signal frequency than it would be when said clipper is disabled.

Claim 21

The invention according to claim 18 wherein said means connecting said output terminal and said device comprise a DC amplifier.

Claim 22

The invention according to claim 18 wherein said superheterodyne signal receiver is a television receiver, said device is a varactor diode and said characteristic is capacitance.

Claim 23

The invention according to claim 20 including a source of DC potential providing a DC voltage equal in magnitude to said predetermined DC reference voltage, means for abling and disabling said automatic frequency control means, and means responsive to disabling of said automatic frequency control means for connecting said source of DC potential and said device to apply said DC voltage of said source to said device.

Claim 24

The invention according to claim 21 wherein said means for connecting said clipper in circuit with said output terminal and for disabling said clipper comprise means connecting said clipper in circuit with said output terminal in response to selection of any one of VHF channels 7 to 13 inclusive and disabling said clipper in response to selection of any one of VHF channels 2 to 6 inclusive.

Claim 25

The invention according to claim 22 wherein said means connecting said output terminal and said device comprise a DC amplifier.

Claim 26

In a superheterodyne signal receiver of a type having a tuner including an oscillator, said tuner being adapted to receive input signals having various carrier frequencies and to provide output signals having different carrier frequencies than the carrier frequencies of said input signals and varying over a range including a predetermined frequency, coarse tuning means for varying the frequency of the signal produced by said oscillator to provide a signal which, when heterodyned with one of said input signals, provides a tuner output signal having a carrier frequency within said range, fine tuning means for varying the frequency of the signal produced by said oscillator over a range in which there is proviDed a signal which, when heterodyned with said one input signal, provides a tuner output signal having a carrier having said predetermined frequency, and automatic frequency control means operable in response to a deviation in the carrier frequency of said output signal of said tuner from said predetermined frequency to automatically vary the frequency of the signal produced by said oscillator in a direction to correct said deviation; the improvement comprising means restricting said fine tuning means from mistuning said oscillator to a point at and beyond which said automatic frequency control means, when abled, is ineffective to correct such mistuning.

Claim 27

In a superheterodyne signal receiver of a type having a tuner including an oscillator, said tuner being adapted to receive input signals having various carrier frequencies and to provide output signals having different carrier frequencies than the carrier frequencies of said input signals and varying over a range including a predetermined frequency, coarse tuning means for varying the frequency of the signal produced by said oscillator to provide a signal which, when heterodyned with one of said input signals, provides a tuner output signal having a carrier frequency within said range, fine tuning means for varying the frequency of the signal produced by said oscillator over a range in which there is proviDed a signal which, when heterodyned with said one input signal, provides a tuner output signal having a carrier having said predetermined frequency, and automatic frequency control means operable in response to a deviation in the carrier frequency of said output signal of said tuner from said predetermined frequency to automatically vary the frequency of the signal produced by said oscillator in a direction to correct said deviation; the improvement comprising means restricting said fine tuning means from mistuning said oscillator to a point at and beyond which said automatic frequency control means, when abled, is ineffective to correct such mistuning.