Abstract: A television tuning system employs a frequency synthesizer system for establishing the tuning of the receiver. A first programmable frequency divider controlled by a reversible counter is connected between the output of a reference oscillator and a phase comparator to which the output of the local oscillator, after passing through another programmable frequency divider, also is applied. The phase comparator output is a tuning voltage used to control the tuning of the local oscillator. A logic circuit is coupled to sense predetermined relationships of signals from a picture carrier detector, a sound carrier detector, an AFT discriminator circuit, and the presence of vertical synchronization signal components for changing the count in the reversible binary counter to adjust the first programmable frequency divider to compensate for channel frequency offsets which may occur in excess of the pull-in range of the AFT discriminator circuit.

Abstract: A television tuning system employs a frequency synthesizer system for establishing the tuning of the receiver. A first programmable frequency divider controlled by a reversible counter is connected between the output of a reference oscillator and a phase comparator to which the output of the local oscillator, after passing through another programmable frequency divider, also is applied. The phase comparator output is a tuning voltage used to control the tuning of the local oscillator. A logic circuit is coupled to sense predetermined relationships of signals from a picture carrier detector, a sound carrier detector, an AFT signal, and the presence of vertical synchronization signal components for changing the count in the reversible binary counter to adjust the first programmable frequency divider to compensate for channel frequency offsets which may occur in excess of the pull-in range of the AFT circuit.

Abstract: A television tuning system employs a frequency synthesizer system for establishing the tuning of the receiver. A programmable frequency divider, controlled by a reversible counter, is connected between the output of a reference oscillator and a phase comparator to which the output of the local oscillator in the tuner also is applied. The phase comparator output provides a tuning voltage for controlling the tuning of the local oscillator. A logic circuit is coupled to sense predetermined relationships of signals from a picture carrier detector, a sound carrier detector, an AFT signal, and the presence of vertical synchronization signal components for changing the count in the reversible binary counter to adjust the programmable frequency divider to compensate for channel frequency offsets which may occur in excess of the pull-in range of the AFT circuit.

Abstract: A wide-band automatic fine tuning (AFT) circuit capable of a .+-.2 MHz pull-in range without false lockups responds to the output of a picture carrier discriminator, a sound carrier discriminator and a vertical synchronizing signal sensing means to operate a reversible digital counter in either its count up or count down direction depending upon the relationship of the outputs of the two discriminators and the synchronizing signal sensing circuit. The output of the counter is supplied to a digital-to-analog converter which produces a tuning control voltage used for controlling the frequency of operation of the local oscillator of the receiver. The output of the digital-to-analog converter is added to a conventional AFT voltage which maintains the desired tuning once it has been established by the wide-band AFT system.