US3801918A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Low-phase-shift incremental fm demodulator
Assignee: United States Department of the Navy
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Filing: 1972-09-15
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Granted: 1974-04-02
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Expires: 1992-09-15
Abstract
Abstract This device demodulates an FM signal by generating switching pulses for each zero crossing of the FM signal. The switching signals are then used to control a charging circuit whose output amplitude is linearly proportional to the modulated frequency and thereby to the original intelligence in amplitude form, used to frequency modulate the carrier. The output is a series of discrete amplitudes forming the envelope of the original information. The device produces a linear correspondence between frequency and amplitude without an intermediate step of removing the carrier in the conventional way by a six pole filter.
Inventors
- 👤 D Milne
- 👤 G Cook
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 01:54
CPC Classifications
H; H03; H03D; H03D3/00; H03D3/02; H03D3/04
Claims Analysis
Total Claims: 27
Claim 1
Independent Claim
72 words
An FM signal demodulator system comprising: first means for determining the period of each half cycle of said FM signal; second means including an output, responsive to said first means, for producing at its output discrete amplitude signals proportional to the period of each said half cycle and being substantially linearly proportional to the frequency of said FM signal; whereby the discrete amplitude signals define the modulating waveform of said FM signal.
Claim 2
Dependent Claim
72 words
An FM signal demodulator system comprising: first means for determining the period of each half cycle of said FM signal; second means including an output, responsive to said first means, for producing at its output discrete amplitude signals proportional to the period of each said half cycle and being substantially linearly proportional to the frequency of said FM signal; whereby the discrete amplitude signals define the modulating waveform of said FM signal.
Claim 3
Dependent Claim
65 words
The system of claim 26 wherein: said second means includes a timer preset to produce at its output a first amplitude signal corresponding to the carrier frequency of said FM signal and at least second and third signals having substantially equal amplitude deviations from said first signal, said second and third signals corresponding to equal frequency deviations from the carrier frequency of said FM signal.
Claim 4
Dependent Claim
44 words
The system of claim 2, wherein: said timer is a Resistance-Capacitance charging circuit having a said time constant T -t/RC for producing a linear proportionality between the frequency of the FM signal and the corresponding amplitude at the output of the said second means.
Claim 5
Dependent Claim
35 words
The system of claim 3, wherein: the number of discrete amplitudes produced per modulation cycle, by said second means, is twice the ratio of the carrier frequency to the modulation frequency of the FM signal.
Claim 6
Dependent Claim
31 words
The system of claim 4, wherein: said first means for determining the periods of each discrete FM pulse generates a pulse for each positive or negative excursion of the FM signal.
Claim 7
Dependent Claim
61 words
The system of claim 5, wherein: said first means includes a one-shot multivibrator responsive to said pulses generated for each positive or negative excursion; said one-shot generating reset pulses and sample pulses; and said second means includes a sampling means including an output for sampling the amplitude of said output signals from said timer circuit in response to a sample pulse.
Claim 8
Dependent Claim
25 words
The system of claim 6, wherein: said sampling means includes holding means for holding said sampled amplitude until the next successive sample pulse is received.
Claim 9
Dependent Claim
44 words
The system of claim 7, wherein: said second means includes reset means for resetting said timer circuit; said means for resetting, discharging said charging circuit and placing said timer circuit in condition for charging to a new amplitude indicative of the corresponding FM frequency.
Claim 10
Dependent Claim
19 words
The system of claim 8, wherein: said reset pulses are produced at the lagging edge of the sample pulses.
Claim 11
Dependent Claim
47 words
The system of claim 9, wherein: said sample means includes a switching means for connecting said charging circuit to said sample and hold circuit in response to said sample pulse; said reset means including means to connect said charging circuit to ground to discharge said charging circuit.
Claim 12
Dependent Claim
46 words
The system of claim 10, including: a filter connected to the output of said sample and hold means to compensate for loss of the peak values of the modulating signal occurring in time between sample pulses, and as reproduced at the sample and hold means output.
Claim 13
Dependent Claim
19 words
The system of claim 11, wherein: said filter response is the reciprocal of the unfiltered sample and hold output.
Claim 14
Dependent Claim
46 words
The system of claim 10, including: a filter connected to the output of said sample and hold circuit to compensate for the diminution of the peaks of the modulation signal occurring in time betWeen sample pulses and as reproduced at the sample and hold circuit output.
Claim 15
Dependent Claim
19 words
The system of claim 13, wherein: said filter response is the reciprocal of the unfiltered sample and hold means.
Claim 16
Dependent Claim
22 words
The system of claim 5, including: means for inverting the said second and third amplitudes with respect to the said first amplitude.
Claim 17
Independent Claim
41 words
A method for FM demodulation, comprising the steps of: determining the period of each discrete F.M. pulse; producing corresponding discrete amplitudes proportional to the said periods and being substantially linearly proportional to the F.M. frequency, for defining the modulating amplitude waveform.
Claim 18
Independent Claim
41 words
A method for FM demodulation, comprising the steps of: determining the period of each discrete F.M. pulse; producing corresponding discrete amplitudes proportional to the said periods and being substantially linearly proportional to the F.M. frequency, for defining the modulating amplitude waveform.
Claim 19
Dependent Claim
34 words
The method of claim 16, wherein: said step of defining the period of each discrete F.M. pulse includes the steps of generating a pulse for each positive or negative excursion of the F.M. wave.
Claim 20
Dependent Claim
36 words
The method of claim 17, wherein: said step of producing corresponding discrete amplitudes includes the step of timing each said generated pulse; and producing an amplitude proportional to the period of each of said generated pulses.
Claim 21
Dependent Claim
28 words
The method of claim 18, wherein: said step of producing proportional amplitudes includes the step of producing amplitudes exponentially related to each said period of said generated pulses.
Claim 22
Dependent Claim
38 words
The method of claim 19, wherein: said step of generating pulses includes the step of producing a number of discrete amplitudes equal to twice the ratio of the carrier frequency to the modulation frequency of the F.M. signal.
Claim 23
Dependent Claim
45 words
The method of claim 20, wherein: said step of producing corresponding discrete amplitudes includes the step of sampling each said exponentially related signal; holding each said sampled signal until the next sampled signal is received; and reconstructing the original amplitude information from each said sample.
Claim 24
Dependent Claim
20 words
The method of claim 21, wherein: said step of reconstructing includes the step of inverting the amplitudes of the samples.
Claim 25
Dependent Claim
62 words
The method of claim 22, wherein: said step of timing includes the step of setting the timer to produce a first amplitude corresponding to the center frequency of the F.M. signal; and said step of inverting includes the step of inverting the sampled amplitudes with respect to said first amplitude to produce an amplitude output substantially linearly proportional to the F.M. frequency.
Claim 26
Dependent Claim
32 words
The method of claim 23, wherein: said step of reconstructing includes the step of filtering the sampled signal to restore the peak values of the modulating signal occurring in time between samples.
Claim 27
Dependent Claim
31 words
The method of claim 24, wherein: said step of reconstructing includes the step of filtering with a filter having a reciprocal relation to the response of the sampling and holding circuit.
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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) | 1977-04-01 | 1977-10-01 | 1978-04-02 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-04-01 | 1981-10-01 | 1982-04-02 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-04-01 | 1985-10-01 | 1986-04-02 | $7700.00 | Window Closed / Lapsed |