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US3581220A
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Frequency modulation signal demodulator
Assignee: Individual
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Filing: 1969-02-17
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Granted: 1971-05-25
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Expires: 1989-02-17
Abstract
Abstract In a data communication system a demodulator for use in detecting data information carried in a frequency modulated signal. A signal which had been modulated between upper and lower limits of frequency, in addition to other frequencies within or without the said limits for supervisory functions, would be received and by means of equalizers, a limiter, zero crossing detector, Schmitt trigger, and a low pass filter, the original data can be recovered from the received frequency modulated signal. Further, circuits are provided for providing phasing information and for detecting the presence or absence of the received carrier frequency signal.
Inventors
- 👤 Allan J Bell
- 👤 Roger B Stone
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-05 10:39
CPC Classifications
H; H03; H03D; H03D3/00; H03D3/02; H03D3/04; H04; H04N; H04N1/00; H04N1/00095; H04N1/32; H04N1/36
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
184 words
A frequency modulation signal demodulator comprising means for receiving said frequency modulation signals and amplifying said signals to a predetermined operating level, means coupled to said amplifying means for equalizing said frequency modulation signals to correct for distortion characteristics present in said signals, means coupled to said equalizing means for symmetrically limiting said frequency modulation signals to substantially rectangular shaped signals retaining the frequency modulated characteristics thereof, first means coupled to said limiting means for generating short duration rectangular shaped pulses in response to the positive and negative going edges of said rectangular shaped signals applied thereto, second means coupled to said first generating means for generating fixed duration pulses in response to said short duration rectangular shaped pulses applied thereto, said second generating means recycling in response to said short duration pulses where said short duration pulses occur during said generation of said fixed duration pulses, and means coupled to said second generating means for filtering said fixed duration pulses into the instantaneous average value signal of said fixed duration pulses applied thereto, said average value signal being the demodulated frequency modulation signal.
Claim 2
Dependent Claim
184 words
A frequency modulation signal demodulator comprising means for receiving said frequency modulation signals and amplifying said signals to a predetermined operating level, means coupled to said amplifying means for equalizing said frequency modulation signals to correct for distortion characteristics present in said signals, means coupled to said equalizing means for symmetrically limiting said frequency modulation signals to substantially rectangular shaped signals retaining the frequency modulated characteristics thereof, first means coupled to said limiting means for generating short duration rectangular shaped pulses in response to the positive and negative going edges of said rectangular shaped signals applied thereto, second means coupled to said first generating means for generating fixed duration pulses in response to said short duration rectangular shaped pulses applied thereto, said second generating means recycling in response to said short duration pulses where said short duration pulses occur during said generation of said fixed duration pulses, and means coupled to said second generating means for filtering said fixed duration pulses into the instantaneous average value signal of said fixed duration pulses applied thereto, said average value signal being the demodulated frequency modulation signal.
Claim 3
Dependent Claim
88 words
The apparatus as set forth in claim 1 further including third means coupled to said filtering means for generating phasing signals for a predetermined period of time at the commencement of operation of said frequency modulation signal demodulator, and means further coupled to said filtering means for detecting the presence of the carrier signal of said frequency modulation signals, said detecting means controlling the operation of said second generating means upon detection of the presence or absence of said carrier signal for a short predetermined period of time.
Claim 4
Dependent Claim
75 words
The apparatus as set forth in claim 1 wherein first generating means comprises means for differentiating said rectangular shaped signals, said differentiated signals comprising positive and negative voltage spike pulses in accordance with the positive and negative going edges, respectively, of said rectangular shaped pulses applied thereto, and fourth means coupled to said differentiating means for generating said short duration pulses for application to said second generating means in response to said voltage spike pulses.
Claim 5
Dependent Claim
48 words
The apparatus as set forth in claim 3 wherein said fourth generating means comprises first and second transistor switch means being enabled by the positive and negative voltage spike pulses, respectively, and transistor inverting means coupled to said first transistor switch means to invert the signals generated thereby.
Claim 6
Dependent Claim
20 words
The apparatus as set forth in claim 1 wherein said second generating means comprises a negative recovery Schmitt trigger circuit.
Claim 7
Dependent Claim
56 words
The apparatus as set forth in claim 1 wherein said symmetrical limiting means comprises first and second diode means for amplitude limiting said frequency modulation signals about the axis determined by the axis of the long term average value of said frequency modulation signals to prevent the leak of the carrier signal into the subsequent circuitry.
Claim 8
Dependent Claim
48 words
The apparatus as set forth in claim 3 wherein said equalizing means includes means for phase equalizing said frequency modulation signals to correct for phase distortion present in said signals, and means for amplitude equalizing said frequency modulation signals to correct for amplitude distortion present in said signals.
Claim 9
Dependent Claim
49 words
The apparatus as set forth in claim 7 wherein said amplifying means includes first means for attenuating signals below a first predetermined frequency, second means for attenuating signals above a second predetermined frequency, said first and second predetermined frequency defining a frequency band wherein said frequency modulation signals occur.
References Cited (Backward Citations)
US3128437A
Cited
US3235812A
Cited
US3353102A
Cited
US3439283A
Cited
US3491305A
Cited
US3493877A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-05-24 | 1974-11-23 | 1975-05-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-05-24 | 1978-11-23 | 1979-05-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-05-24 | 1982-11-23 | 1983-05-25 | $7700.00 | Window Closed / Lapsed |