US3796824A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Tv afc circuit eliminates biased diodes for symmetrical pull-in
Assignee: Zenith Electronics LLC
•
Filing: 1972-01-26
•
Granted: 1974-03-12
•
Expires: 1992-01-26
Abstract
Abstract The automatic frequency control (AFC) system of a television receiver includes a discriminator network and a pair of nonbiased rectifier arrangements with load circuits, operating over a small range of frequency deviations centered about the desired mean frequency. The rectifier arrangements are non-biased for compatibility with varactor tuning systems and include three serially connected diodes in one of the rectifier arrangements and a single diode in the other to achieve extended pull-in. The three serially connected diodes vary the conduction threshold of the positive portion of the discriminator network to assure proper shaping of the frequency response characteristic of the FM detector. Accordingly, for conditions of gross mistuning, control voltages are obtained from the two rectifier arrangements that are of the same polarity and aid one another in obtaining an augmented frequency correcting effect.
Inventors
- 👤 R Baker
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 20:22
CPC Classifications
H; H04; H04N; H04N5/00; H04N5/44; H04N5/50; H03; H03J; H03J7/00; H03J7/02; H03J7/04; H03J7/08; H03J7/10
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
233 words
In a television receiver having a tunable input stage of the varactor type for selecting a particular broadcast channel comprising a video modulated carrier and an audio modulated carrier having a fixed frequency separation from one another and for deriving therefrom an intermediate frequency signal having video and audio IF components of desired respective values, an automatic frequency control system comprising: means including a discriminator network having a pair of output terminals and a pair of non-biased rectifier arrangements with different conduction threshold levels individually connected to respective ones of said output terminals of said network, said means being responsive to said intermediate frequency signal for developing a first control effect at one of said output terminals of a predetermined polarity and of a magnitude dependent upon deviation in a predetermined direction of the actual frequency of said video IF component from its aforesaid desired value, and for concurrently developing a second control effect at the other of said output terminals of the same predetermined polarity and of a magnitude dependent upon deviation in said predetermined direction of the actual frequency of said audio IF component from its aforesaid desired value; means coupling said output terminals to said tunable input stage; and means for utilizing both of said control effects to control said varactor tunable input stage and maintain the frequencies of said video and audio IF components at their aforesaid desired values.
Claim 2
Dependent Claim
233 words
In a television receiver having a tunable input stage of the varactor type for selecting a particular broadcast channel comprising a video modulated carrier and an audio modulated carrier having a fixed frequency separation from one another and for deriving therefrom an intermediate frequency signal having video and audio IF components of desired respective values, an automatic frequency control system comprising: means including a discriminator network having a pair of output terminals and a pair of non-biased rectifier arrangements with different conduction threshold levels individually connected to respective ones of said output terminals of said network, said means being responsive to said intermediate frequency signal for developing a first control effect at one of said output terminals of a predetermined polarity and of a magnitude dependent upon deviation in a predetermined direction of the actual frequency of said video IF component from its aforesaid desired value, and for concurrently developing a second control effect at the other of said output terminals of the same predetermined polarity and of a magnitude dependent upon deviation in said predetermined direction of the actual frequency of said audio IF component from its aforesaid desired value; means coupling said output terminals to said tunable input stage; and means for utilizing both of said control effects to control said varactor tunable input stage and maintain the frequencies of said video and audio IF components at their aforesaid desired values.
Claim 3
Dependent Claim
70 words
An automatic frequency control system in accordance with claim 1 wherein one of said non-biased rectifier arrangements includes a single diode and the other of said non-biased rectifier arrangements comprises a multiplicity of serially connected diodes for developing said different conduction threshold levels to shape the frequency response characteristic of said discriminator network in a manner required to accomplish derivation of said first and second control effects of like polarity.
Claim 4
Dependent Claim
20 words
An automatic frequency control system in accoRdance with claim 2 wherein said multiplicity of serially connected diodes comprises three diodes.
Claim 5
Dependent Claim
33 words
An automatic frequency control system in accordance with claim 1 wherein said non-biased rectifier arrangements have load circuits coupled in series opposition to one another for developing said first and second control effects.
Claim 6
Dependent Claim
35 words
An automatic frequency control system in accordance with claim 1 wherein the magnitude of said second control effect is proportional to the deviation of the actual frequency of said audio component from its desired value.
Claim 7
Dependent Claim
51 words
An automatic frequency control system in accordance with claim 1 wherein the second control effect is derived over a range of frequency deviations of said audio IF component which is approximately equal to half the frequency spacing of said desired frequencies of said video IF component and said audio IF component.
Claim 8
Dependent Claim
105 words
An automatic frequency control system in accordance with claim 1 wherein the magnitude of said first control effect increases proportionally with deviations to a maximum value at a given frequency between said desired frequency of said video IF component and another IF frequency representing the sound carrier of the adjacent broadcast channel and decreases to zero as the frequency of said video IF component approaches said second IF frequency, and further in which the magnitude of said second control effect increases proportionally with deviations of said audio IF component which accompany deviations of said video IF component between said given frequency and said IF frequency.
Claim 9
Dependent Claim
32 words
An automatic frequency control system in accordance with claim 7 wherein the magnitude of said second control effect decreases toward zero for still greater deviations in frequency of said audio IF component.
Claim 10
Dependent Claim
123 words
An automatic frequency control system in accordance with claim 1 wherein variations of said first control effect with frequency deviation has a predetermined slope over a predetermined range centered about said desired video IF frequency but has an opposite slope for deviations from the highest amplitude frequency point of said range to another IF frequency representing the sound carrier of the adjacent broadcast channel, further in which varitions of said second control effect with frequency deviation has said predetermined slope over another range extending from said desired audio IF frequency to higher frequencies, and in which the frequency span of said other range is at least approximately equal to the frequency spacing of said desired video IF frequency from said other IF frequency.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-03-11 | 1977-09-10 | 1978-03-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-03-11 | 1981-09-10 | 1982-03-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-03-11 | 1985-09-10 | 1986-03-12 | $7700.00 | Window Closed / Lapsed |