Automatic frequency control for digital tuning systems

Claim 2

In combination, a varactor tuner for providing an intermediate frequency signal in response to a radio frequency signal, a tuning system of the type wherein a binary word is used to develop a tuning voltage for selecting the tuning frequency of said varactor tuner, an automatic frequency control apparatus comprising a frequency discriminator for providing a signal indicative of the direction of a tuning error in response to said intermediate frequency signal, and means for modifying said binary word in response to said discriminator signal to minimize said tuning error.

Claim 3

The apparatus of claim 1 further comprising means for inhibiting the modifying of said binary word when a received radio frequency signal is below a minimum threshold level.

Claim 4

An automatic frequency control circuit for a receiver having a varactor tuner for producing an intermediate frequency signal and a tuning system of the type wherein a digital counter produces a binary word, said binary word being thereafter converted into a tuning voltage for selecting the tuning frequency of said varactor tuner comprising: (a) a frequency discriminator operatively connected to said varactor tuner for producing a signal for indicating a tuning error in response to said intermediate frequency signal; (b) detector means operatively connected to said frequency discriminator for determining the direction of said tuning error; and (c) means for modifying said counter contents in response to said detector means whereby said tuning error is reduced.

Claim 5

An automatic frequency control circuit for a receiver having a varactor tuner for producing an intermediate frequency signal and a tuning system of the type wherein a digital counter produces a binary word, said binary word being thereafter converted into a tuning voltage for selecting the tuning frequency of said varactor tuner comprising: (a) a frequency discriminator operatively connected to said varactor tuner for producing a signal for indicating a tuning error in response to said intermediate frequency signal; (b) detector means operatively connected to said frequency discriminator for determining the direction of said tuning error; and (c) means for modifying said counter contents in response to said detector means whereby said tuning error is reduced.

Claim 6

The apparatus of claim 3 further comprising threshold detection means for determining when a received signal exceeds a threshold level and means for inhibiting said means for modifying said counter contents in response to said threshold detection means.

Claim 7

An automatic frequency control circuit for maintaining tuning of a digital tuning system of the type wherein the contents of a binary counter establish a tuning voltage, comprising: (a) discriminator means for indicating a tuning error; (b) means for producing a first voltage when a positive tuning error in excess of a predetermined minimum exists; (c) means for producing a second voltage when a negative tuning error in excess of a predetermined minimum exists; (d) an OR gate for receiving said first voltage and said second voltage; (e) means for supplying clock pulses to said binary counter in response to said OR gate output voltage; and (f) a polarity detector for receiving said discriminator means output, said polarity detector operatively connected to said binary counter whereby said binary counter will increment or decrement reducing said tuning error.

Claim 8

An automatic frequency control circuit for maintaining tuning of a digital tuning system of the type wherein the contents of a binary counter establish a tuning voltage, comprising: (a) discriminator means for indicating a tuning error; (b) means for producing a first voltage when a positive tuning error in excess of a predetermined minimum exists; (c) means for producing a second voltage when a negative tuning error in excess of a predetermined minimum exists; (d) an OR gate for receiving said first voltage and said second voltage; (e) means for supplying clock pulses to said binary counter in response to said OR gate output voltage; and (f) a polarity detector for receiving said discriminator means output, said polarity detector operatively connected to said binary counter whereby said binary counter will increment or decrement reducing said tuning error.

Claim 9

The apparatus of claim 5 further comprising means for inhibiting said clock pulses when a received signal level is below a predetermined threshold level.

Claim 10

In combination, a varactor tuner for providing an intermediate frequency signal in response to a radio frequency signal, a tuning system of the type wherein a binary word is used to develop a tuning voltage for selecting the tuning frequency of a varactor tuner, an automatic frequency control apparatus comprising a frequency discriminator for providing a tuning signal indicative of the magnitude and direction of a tuning error in response to said intermediate frequency signal, means for detecting when said tuning error exceeds a threshold level, and means for modifying said binary word to minimize said tuning error when said tuning error exceeds said threshold level.

Claim 11

In combination, a varactor tuner for providing an intermediate frequency signal in response to a radio frequency signal, a tuning system of the type wherein a binary word is used to develop a tuning voltage for selecting the tuning frequency of a varactor tuner, an automatic frequency control apparatus comprising a frequency discriminator for providing a tuning signal indicative of the magnitude and direction of a tuning error in response to said intermediate frequency signal, means for detecting when said tuning error exceeds a threshold level, and means for modifying said binary word to minimize said tuning error when said tuning error exceeds said threshold level.

Claim 12

The apparatus of claim 7 further comprising means for inhibiting the modifying of said binary word when a received radio frequency signal is below a minimum threshold level.