US4728957A
Expired / Lapsed
US
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Digital frequency discriminator, for extracting a sinusoidal signal
Assignee: Thomson TRT Defense
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Filing: 1986-11-24
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Granted: 1988-03-01
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Expires: 2006-11-24
Abstract
Abstract A digital frequency discriminator designed to extract from a carrier at frequency f o a low frequency sinusoidal signal modulating the carrier. It receives digital samples x n from the carrier modulated at the frequency f e =4f o and includes: means of accumulation of N samples x n first means of storage of coefficients R 01 , R 02 , R 11 and R 12 defined by: ##EQU1## means for formatting the coefficients R ab , and first means of computing the quantity a 1 defined by: ##EQU2## the quantity a 1 , similar to one point of the sought sinusoid, being then transferred into second means of storage, after which the next point of the sinusoid is determined from the next N samples.
Inventors
- 👤 Serge Hethuin
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 20:20
CPC Classifications
G; G01; G01S; G01S1/00; G01S1/02; G01S1/08; G01S1/44; G01S1/46; G01S1/50; H; H03; H03D; H03D3/00; H03D3/006; H03D2200/00; H03D2200/0041; H03D2200/006; H03D2200/0062
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
209 words
A digital frequency discriminator for extracting from a FM signal having a carrier frequency of f o at least one low frequency sinusoidal signal of frequency F which frequency modulates the carrier with a modulating frequency excursion ΔF, the value of f o and ΔF being known, characterized in that said discriminator comprises: (a) means for selectively pre-filtering digital samples e n of the FM signal to produce samples x n modulated at a frequency f e =4f o ; (b) accumulation means for accumulating, in an interval between two successive times t q and t q+1 , N successive ones of the digital samples x n which form an analysis window, the frequency of the modulated signal being considered constant during this interval; (c) first storage means for storing coefficients R 01 , R 02 , R 11 , R 12 and R 22 defined by: ##EQU49## (d) computing means for determining the quantity a 1 defined by: ##EQU50## the quantity a 1 approximating the ordinate of a point on a curve representing the low frequency sinusoidal signal; and (e) second storage means for storing the value of a 1 , while the computing means determines a quantity approximating the ordinate of a subsequent point on the curve.
Claim 2
Dependent Claim
209 words
A digital frequency discriminator for extracting from a FM signal having a carrier frequency of f o at least one low frequency sinusoidal signal of frequency F which frequency modulates the carrier with a modulating frequency excursion ΔF, the value of f o and ΔF being known, characterized in that said discriminator comprises: (a) means for selectively pre-filtering digital samples e n of the FM signal to produce samples x n modulated at a frequency f e =4f o ; (b) accumulation means for accumulating, in an interval between two successive times t q and t q+1 , N successive ones of the digital samples x n which form an analysis window, the frequency of the modulated signal being considered constant during this interval; (c) first storage means for storing coefficients R 01 , R 02 , R 11 , R 12 and R 22 defined by: ##EQU49## (d) computing means for determining the quantity a 1 defined by: ##EQU50## the quantity a 1 approximating the ordinate of a point on a curve representing the low frequency sinusoidal signal; and (e) second storage means for storing the value of a 1 , while the computing means determines a quantity approximating the ordinate of a subsequent point on the curve.
Claim 3
Dependent Claim
65 words
A digital frequency discriminator as in claim 1 including: (a) second computing means for determining the quantity a 2 defined by: ##EQU51## the quantity a 2 indicating convergence; and (b) comparison means for comparing the quantity a 2 with two thresholds s 1 and s 2 , a 1 being transferred into the second storage means only if s 1 <s 2 <s 2 .
Claim 4
Dependent Claim
35 words
A digital frequency discriminator as in claim 2 including third computing means for determining the quantity σ 2 representing the noise power of the sampled signal and defined by: σ.sup.2 =1/N(R.sub.0 +a.sub.1 R.sub.01 +a.sub.2 R.sub.02).
Claim 5
Dependent Claim
70 words
A digital frequency discriminator as in claim 1, 2 or 3 where the means for selectively prefiltering the digital samples e n comprises a bandpass filter having a center frequency f o for prefiltering the samples e n when the noise power of the modulated carrier is detected as being lower than a threshold S" which corresponds to a value of the signal-to-noise ratio on the order of 15 dB.
Claim 6
Dependent Claim
45 words
A digital frequency discriminator as in claim 4 where the bandpass filter comprises means for performing an elementary band-pass filtering of the type: x.sub.n =1/8(e.sub.n -e.sub.n-2 +e.sub.n-4 -e.sub.n-6 +e.sub.n-8 -e.sub.n-10 +e.sub.n-12 -e.sub.n-14) where e n to e n-14 designate the digital samples of the carrier.
Claim 7
Dependent Claim
65 words
A digital frequency discriminator as in claim 1, 2 or 3 including fourth computing means for determining the quantity: v.sub.q =a.sub.1q +2 cos 2kπ/M v.sub.q-1 -v.sub.1-2, where the quantity a 1q /√a 2q can be substituted for a 1q , and where v -2 =v -1 =0, the index q varying from 0 to M-1, and k and M being positive integers such that: ##EQU52##
Claim 8
Dependent Claim
49 words
A digital frequency discriminator as in claim 1, 2 or 3 for extracting a reference phase contained in composite VOR signal received by a VOR-ILS equipment, by point-by-point restoration of a 30 Hz sinusoidal signal defining said reference phase, where f o =9960 Hz and Δ F =480 Hz.
Claim 9
Dependent Claim
141 words
A digital frequency discriminator as in claim 1, 2 or 3 for extracting a reference phase contained in a composite VOR signal received by a VOR-ILS equipment, by point-by-point restoration of a 30 Hz sinusoidal signal defining said reference phase, where f o =3320 Hz, and further including: (a) an analog one-way filter of order less than or equal to three for filtering a 9960 Hz carrier of the VOR signal, said one-way filter having a pass band between 0 and 10600 Hz and having a transition band between 10600 Hz and 15960 Hz; (b) means for sampling a signal obtained at an output of the one-way filter at a frequency of 26560 Hz; and (c) a half-band filter having 4 distinct coefficients for filtering the samples, and having a high pass output connected to the input of the digital discriminator.
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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) | 1991-03-01 | 1991-08-31 | 1992-03-01 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1995-03-01 | 1995-08-31 | 1996-03-01 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1999-03-01 | 1999-08-31 | 2000-03-01 | $7700.00 | Window Closed / Lapsed |