Phase locked loop tuning control system including a sync activated AFT signal seeking arrangement

Claim 1

In a multiband television receiver including channel selection means for selecting channels; RF means for selecting an RF carrier corresponding to a selected channel in response to the magnitude of a tuning control signal; local oscillator means for generating a local oscillator signal with a frequency corresponding to the selected channel; mixer means for combining said selected RF carrier and said local oscillator signal to produce an IF signal including a picture carrier having a frequency with a predetermined nominal value; an automatic fine tuning (AFT) discriminator for generating an AFT signal having an amplitude representing the deviation of the frequency of siad picture carrier from said nominal value; and a synchronization processing section for generating at least one synchronization signal; apparatus comprising: reference frequency means for generating a reference frequency signal; comparison means for generating an error signal representing the phase and/or frequency deviation between said local oscillator signal and a comparison signal having a frequency substantially equal to the product of a programmable factor and the frequency of said reference signal; programmable factor control means for controlling the programmable factor, said programmable factor control means setting said programmable factor in response to the channel number of the selected channel when a new channel is selected; lock detector means for determining when said error signal has a predetermined condition; tuning signal generating means for generating said tuning signal in response to one of said error and AFT signals; mode selection means for selectively coupling one of said AFT signal and said error signal to said tuning signal generating means, said mode selection means being responsive to said channel selection means for coupling said error signal to said tuning control means when said channel is changed and being responsive to said lock detector means to couple said AFT signal to said tuning signal generating means when said error signal has said predetermined condition; offset detector means for determining when said local oscillator signal has a predetermined frequency offset from the frequency established when said error signal was coupled to said tuning signal generating means after said AFT signal is coupled to said tuning signal generating means; said mode selection means being responsive to said offset detector means for coupling said error signal to said tuning signal generating means when said local oscillator signal has said predetermined frequency offset; said programmable factor control means being responsive to said offset detector means for changing said programmable factor by a predetermined increment when said local oscillator signal has said predetermined frequency offset; synchronization detector means for determining when said synchronization signal has a predetermined condition; and AFT control means responsive to said sync detector means for decoupling said AFT signal from said tuning signal generating means and instead coupling a predetermined level selected to cause said local oscillator signal to have said predetermined value to said tuning signal generating means when said synchronization signal has said predetermined condition.