Patent US3980968A successfully refreshed from Google Patents.
US3980968A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Non-proportionate AFC system
Assignee: Zenith Electronics LLC
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Filing: 1975-01-02
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Granted: 1976-09-14
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Expires: 1995-01-02
Abstract
Abstract A television tuning system has a ramp voltage source including an electrical current source and an electrical current sink coupled through selectively operable transmission gates for varying the voltage of a tuning capacitor to control a local oscillator for tuning independent of received signal. The local oscillator signal is mixed with a received signal to produce an intermediate frequency signal which is amplified in an IF amplifier. A frequency detector is coupled to the IF amplifier and produces an error signal dependent upon the frequency difference between a reference frequency and the IF signal. An additional current source and sink are coupled to the tuning capacitor through transmission gates controlled by the error signals. Differences greater than a predetermined amount selectively activate the latter transmission gates to provide substantially constant magnitude tuning voltage corrections irrespective of the amount of the difference.
Inventors
- 👤 John Y. Ma
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 23:18
CPC Classifications
H; H03; H03J; H03J7/00; H03J7/18; H03J7/20; H03J7/24; H03J7/26
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
114 words
In a television tuning system including a variable frequency local oscillator, means determining the frequency of said local oscillator independently of broadcast television signals, mixing means mixing the local oscillator signal with a received television signal to produce an IF signal, an IF signal amplifier and tuning control means for said local oscillator, received signal tracking means comprising: detector means coupled between said IF amplifier and said tuning control means for developing an error signal as a function of the frequency difference between said IF signal and a reference frequency, and means in said tuning control means for producing a constant magnitude correction signal for said local oscillator in response to said error signal.
Claim 2
Dependent Claim
114 words
In a television tuning system including a variable frequency local oscillator, means determining the frequency of said local oscillator independently of broadcast television signals, mixing means mixing the local oscillator signal with a received television signal to produce an IF signal, an IF signal amplifier and tuning control means for said local oscillator, received signal tracking means comprising: detector means coupled between said IF amplifier and said tuning control means for developing an error signal as a function of the frequency difference between said IF signal and a reference frequency, and means in said tuning control means for producing a constant magnitude correction signal for said local oscillator in response to said error signal.
Claim 3
Dependent Claim
31 words
The received signal tracking means in claim 1 wherein said tuning control means includes a tuning capacitor for developing a tuning voltage and voltage means for charging and discharging said capacitor.
Claim 4
Dependent Claim
35 words
The received signal tracking means in claim 2 wherein said detector means develops positive and negative polarity error signals dependent upon whether the frequency of said IF signal is above or below said reference frequency.
Claim 5
Dependent Claim
58 words
The received signal tracking means of claim 3 wherein said voltage means include an electrical power source and sink and corresponding transmission gates coupled between said source and sink and said tuning capacitor, respectively; one of said transmission gates responding to said negative polarity error signals and the other transmission gate responding to said positive polarity error signals.
Claim 6
Dependent Claim
39 words
The received signal tracking means of claim 4 wherein said source and said sink are equal electrical current capacity to provide a constant current correction to said tuning capacitor regardless of the magnitude and polarity of said error signals.
Claim 7
Dependent Claim
33 words
The received signal tracking means of claim 5 wherein said transmission gates are activated only when said frequency difference between said IF signal and said reference frequency is greater than a predetermined amount.
Claim 8
Dependent Claim
122 words
In a television tuning system of the type including tuning control means supplying tuning voltage to a local oscillator in response to signal-independent tuning means, mixing means mixing the local oscillator signal with a received television signal to derive an intermediate frequency signal and signal tracking automatic frequency control means producing an error signal as a function of frequency difference between said intermediate frequency signal and a reference frequency, the improvement in said automatic frequency control means comprising: means in said tuning control means for incrementally changing said tuning voltage to reduce said error signal in a non-proportionate manner, said means being disabled when the frequency difference between said IF signal and said reference frequency is less than a predetermined threshold value.
Claim 9
Dependent Claim
122 words
In a television tuning system of the type including tuning control means supplying tuning voltage to a local oscillator in response to signal-independent tuning means, mixing means mixing the local oscillator signal with a received television signal to derive an intermediate frequency signal and signal tracking automatic frequency control means producing an error signal as a function of frequency difference between said intermediate frequency signal and a reference frequency, the improvement in said automatic frequency control means comprising: means in said tuning control means for incrementally changing said tuning voltage to reduce said error signal in a non-proportionate manner, said means being disabled when the frequency difference between said IF signal and said reference frequency is less than a predetermined threshold value.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1979-09-14 | 1980-03-15 | 1980-09-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1983-09-14 | 1984-03-15 | 1984-09-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1987-09-14 | 1988-03-15 | 1988-09-14 | $7700.00 | Window Closed / Lapsed |