Frequency counter for a television tuning system
First Claim
1. In a system for tuning a television receiver to the various channels a viewer may select, apparatus comprising:
- local oscillator means for generating a local oscillator signal;
counter means for generating a frequency divided signal by counting a predetermined number of periods of said local oscillator signal, said predetermined number being proportional to the frequency of said local oscillator signal;
means for generating a reference frequency signal;
phase control means for generating a control signal representing the phase and frequency deviation between said frequency divided signal and said reference frequency signal;
mode switching means for selectively coupling said control signal to said local oscillator means;
said mode switching means initially coupling said control signal to said local oscillator means;
said local oscillator means changing the frequency of said local oscillator signal in response to said control signal until said frequency divided signal and said reference frequency signal to be in a predetermined phase and frequency relation;
said counter means accumulating a nominal number of counts during a predetermined portion of said frequency divided signal when said frequency divided signal and said reference signal are in said predetermined phase and frequency relationship;
means for generating a lock signal when said frequency divided signal and said reference frequency signal are in said predetermined phase and frequency relationship;
said mode switching means decoupling said control signal from said local oscillator means in response to said lock signal;
means for generating a count signal when said control signal is decoupled from said local oscillator means, said count signal having a duration with a predetermined time relationship to said reference frequency signal;
means responsive to said count signal for disabling said counter means from counting when said control signal is decoupled from said local oscillator means except during the duration of said count signal; and
means for generating an offset signal representing the deviation between the count accumulated by said counter means during a time interval corresponding to said predetermined portion of said frequency divided signal when said control signal is decoupled from said local oscillator means and said nominal number of counts, said offset signal being coupled to said mode switching means to control the coupling of said control signal to said local oscillator means.
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Accused Products
Abstract
A tuning system for a television receiver includes a local oscillator which is controlled first by a phase lock loop arrangement and then by an AFT discriminator arrangement for tuning the receiver to non-standard as well as standard frequency carriers. The phase lock loop arrangement includes a programmable divider for dividing the local oscillator frequency by a programmable factor corresponding to the presently selected channel. When the local oscillator is being controlled by the AFT discriminator arrangement, the count accumulated by the programmable divider during a reference interval determines how far the local oscillator frequency has drifted from its nominal value. If a predetermined frequency offset has been exceeded, control is returned to phase lock loop control and the programmable factor is incrementally changed.
24 Citations
13 Claims
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1. In a system for tuning a television receiver to the various channels a viewer may select, apparatus comprising:
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local oscillator means for generating a local oscillator signal; counter means for generating a frequency divided signal by counting a predetermined number of periods of said local oscillator signal, said predetermined number being proportional to the frequency of said local oscillator signal; means for generating a reference frequency signal; phase control means for generating a control signal representing the phase and frequency deviation between said frequency divided signal and said reference frequency signal; mode switching means for selectively coupling said control signal to said local oscillator means;
said mode switching means initially coupling said control signal to said local oscillator means;said local oscillator means changing the frequency of said local oscillator signal in response to said control signal until said frequency divided signal and said reference frequency signal to be in a predetermined phase and frequency relation; said counter means accumulating a nominal number of counts during a predetermined portion of said frequency divided signal when said frequency divided signal and said reference signal are in said predetermined phase and frequency relationship; means for generating a lock signal when said frequency divided signal and said reference frequency signal are in said predetermined phase and frequency relationship; said mode switching means decoupling said control signal from said local oscillator means in response to said lock signal; means for generating a count signal when said control signal is decoupled from said local oscillator means, said count signal having a duration with a predetermined time relationship to said reference frequency signal; means responsive to said count signal for disabling said counter means from counting when said control signal is decoupled from said local oscillator means except during the duration of said count signal; and means for generating an offset signal representing the deviation between the count accumulated by said counter means during a time interval corresponding to said predetermined portion of said frequency divided signal when said control signal is decoupled from said local oscillator means and said nominal number of counts, said offset signal being coupled to said mode switching means to control the coupling of said control signal to said local oscillator means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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Specification