US3674935A
Expired / Lapsed
US
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Digital circuit demodulator for frequency-shift data signals
Assignee: AT&T Inc
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Filing: 1970-10-07
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Granted: 1972-07-04
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Expires: 1990-10-07
Abstract
Abstract FSK data signals are applied to a digital phase-locked loop having a countdown feedback circuit producing a signal wave which leads or lags the phase of the data signal by an angle which is dependent on the frequency of the data signal. The countdown circuit also generates a second signal wave which lags the phase of the feedback wave by a fixed angle. The unique permutations of concurrent amplitudes of the three signals are processed by sets of gates to recover the baseband signal. Counters monitor the outputs of the gates to detect steady tone signals and loss of carrier.
Inventors
- 👤 Thomas Russell Lawrence
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 21:34
CPC Classifications
H; H04; H04L; H04L27/00; H04L27/10; H04L27/14
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
94 words
A frequency discriminator for a frequency-shift signal comprising: means for accepting the frequency shift signal means responsive to the accepting means for producing a first signal wave leading and lagging in phase in accordance with the frequency of the frequency-shift signal, means responsive to the accepting means for generating a second signal wave differing in phase from the first signal wave by a fixed angle other than 180*, and digital logic means for processing the concurrent amplitude levels of the frequency-shift signal and the first and second signal waves to recover the baseband signal.
Claim 2
Dependent Claim
94 words
A frequency discriminator for a frequency-shift signal comprising: means for accepting the frequency shift signal means responsive to the accepting means for producing a first signal wave leading and lagging in phase in accordance with the frequency of the frequency-shift signal, means responsive to the accepting means for generating a second signal wave differing in phase from the first signal wave by a fixed angle other than 180*, and digital logic means for processing the concurrent amplitude levels of the frequency-shift signal and the first and second signal waves to recover the baseband signal.
Claim 3
Dependent Claim
33 words
A frequency discriminator in accordance with claim 1 wherein the digital logic means includes gate means for examining the concurrent amplitude levels of the frequency-shift signal and the first and second signal waves.
Claim 4
Dependent Claim
39 words
A frequency discriminator in accordance with claim 2 wherein the gate means comprise a plurality of gates, each gate having an input thereto responsive to an individual one of the frequency-shift signal and the first and second signal waves.
Claim 5
Dependent Claim
30 words
A frequency discriminator in accordance with claim 3 wherein certain of the gate inputs include means for inverting the frequency-shift signal and the first and second signal waves individual thereto.
Claim 6
Dependent Claim
48 words
A frequency discriminator in accordance with claim 3 wherein the plurality of gates define sets of gates, each set arranged to detect unique permutations of amplitude levels of the frequency-shift signal and the first and second signal waves which occur for an individual frequency of the frequency-shift signal.
Claim 7
Dependent Claim
28 words
A frequency discriminator in accordance with claim 5 wherein bistable means responsive to the sets of gates reproduces the baseband signal in the form of a binary signal.
Claim 8
Dependent Claim
45 words
A frequency discriminator in accordance with claim 5 further including means to count the output of one of the sets of gates to thereby determine the duration of the steady tone of the frequency-shift signal at the frequency individual to the one set of gates.
Claim 9
Dependent Claim
31 words
A frequency discriminator in accordance with claim 7 wherein said count means includes reset means responsive to transitions of the baseband signal to reset the count means to an initial condition.
Claim 10
Dependent Claim
69 words
A frequency discriminator in accordance with claim 6 which further includes means responsive to the bistable means for counting transitions of the baseband binary signal a fixed interval having a duration less than the bit interval of the baseband signal and including means for providing an output signal when a plurality of baseband signal transitions occur within the fixed interval to thereby indicate a loss of frequency-shift signal carrier.
Claim 11
Dependent Claim
89 words
A frequency discriminator for a frequency-shift signal comprising: a phase-locked loop for producing a first signal wave which leads and lags the phase of the frequency-shift signal, means for producing a second signal wave differing in phase from the frequency-shift signal, the first signal wave, an inversion of the frequency-shift signal and an inversion of the first signal wave for at least one frequency of the frequency-shift signal, and digital logic means for processing the frequency-shift signal and the first and second signal waves to recover the baseband signal.
Claim 12
Dependent Claim
89 words
A frequency discriminator for a frequency-shift signal comprising: a phase-locked loop for producing a first signal wave which leads and lags the phase of the frequency-shift signal, means for producing a second signal wave differing in phase from the frequency-shift signal, the first signal wave, an inversion of the frequency-shift signal and an inversion of the first signal wave for at least one frequency of the frequency-shift signal, and digital logic means for processing the frequency-shift signal and the first and second signal waves to recover the baseband signal.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-07-04 | 1976-01-03 | 1976-07-04 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-07-04 | 1980-01-03 | 1980-07-04 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-07-04 | 1984-01-03 | 1984-07-04 | $7700.00 | Window Closed / Lapsed |