US3660601A
Expired / Lapsed
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Frequency detection system
Assignee: International Business Machines Corp
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Filing: 1970-06-10
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Granted: 1972-05-02
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Expires: 1990-06-10
Abstract
Abstract A system for detecting frequency shift keying information on a real time basis independent of the amplitude of the input FSK signal. The second derivative of the input voltage waveform signal which is in exact phase with the input signal is obtained. The gain of the differentiated voltage signal is controlled so that when the input signal has a frequency below predetermined frequency, the magnitude o2 the differentiated voltage signal will be less than the magnitude of the input voltage signal at all points except zero; and when the input signal exceeds the predetermined frequency, the magnitude of the differentiated voltage signal exceeds that of the input voltage signal. The input signal and the gain controlled differentiated signal are magnitude compared and an output signal representative of the result of the comparison and hence of the frequency of the input signal is supplied. A low pass filter introducing minimal signal delay is utilized to remove possible logic silvers at the time when both signals are zero and when there is an input frequency change.
Inventors
- 👤 Donald R Dobson
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 22:21
CPC Classifications
H; H04; H04L; H04L27/00; H04L27/10; H04L27/14
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
189 words
A system for detecting a frequency shift signal representative of binary data comprising: conveying means for conveying a frequency shift signal representative of binary data having at least a first frequency and a second frequency; differentiating means connected to the conveying means and responsive to said frequency shift signal for differentiating the frequency shift signal with respect to time and for providing a differentiated signal representative of the second derivative with respect to time of the frequency shift signal; gain control means for controlling the gain of at least one of the differentiated signal and the frequency shift signal so that the relative gain of the differentiated signal is proportional to the reciprocal of the square of a frequency intermediate said first frequency and said second frequency; means for inverting one of said frequency shift signal and said differentiated signal; comparing means for comparing the magnitude of said inverted signal and the other of said signals and for providing a binary output signal representative of the result of said comparison, said binary output signal corresponding to the binary significance of the frequency shift signal conveyed by the conveying means.
Claim 2
Independent Claim
189 words
A system for detecting a frequency shift signal representative of binary data comprising: conveying means for conveying a frequency shift signal representative of binary data having at least a first frequency and a second frequency; differentiating means connected to the conveying means and responsive to said frequency shift signal for differentiating the frequency shift signal with respect to time and for providing a differentiated signal representative of the second derivative with respect to time of the frequency shift signal; gain control means for controlling the gain of at least one of the differentiated signal and the frequency shift signal so that the relative gain of the differentiated signal is proportional to the reciprocal of the square of a frequency intermediate said first frequency and said second frequency; means for inverting one of said frequency shift signal and said differentiated signal; comparing means for comparing the magnitude of said inverted signal and the other of said signals and for providing a binary output signal representative of the result of said comparison, said binary output signal corresponding to the binary significance of the frequency shift signal conveyed by the conveying means.
Claim 3
Dependent Claim
39 words
The system set forth in claim 1 further comprising: a wide bandwidth low pass filter responsive to the binary output signal of the comparing means for filtering logic slivers occurring at the zero crossover points of the compared signals.
Claim 4
Dependent Claim
72 words
The system set forth in claim 1 wherein said comparing means comprises a difference amplifier responsive to said inverted signal and the other of said signals for providing an output signal whenever a selected one of said signals is more positive than the other of said signals, and logic switching means responsive to the output signal of the difference amplifier and to the frequency shift signal for providing said binary output signal.
Claim 5
Dependent Claim
105 words
The system set forth in claim 1 wherein said differentiating means and said gain control means comprises two cascaded circuits, the first of said circuits being responsive to said conveying means for differentiating said frequency shift signal with respect to time and the second of said circuits being responsive to the output differentiated signal of said first circuit for differentiating said output differentiated signal with respect to time and providing an output signal representative of the second derivative with respect to time of the frequency shift signal, the gain of said cascaded circuits being proportional to the reciprocal of the square of said intermediate frequency.
Claim 6
Independent Claim
142 words
A method for detecting the binary significance of a frequency shift signal having at least a first frequency and a second frequency representative of binary data comprising the steps of: differentiating the frequency shift signal to obtain a differentiated signal representative of the second derivative with respect to time of the frequency shift signal; controlling the gain of at least one of the differentiated signal and the frequency shift signal so that the relative gain of the differentiated signal is proportional to the reciprocal of the square of a frequency intermEdiate the first and second frequencies of the frequency shift signal; inverting one of said differentiated signal and said frequency shift signal; comparing the magnitude of the inverted signal with the other of said signals; indicating the binary significance of the frequency shift signal in accordance with the result of the comparison.
Claim 7
Independent Claim
142 words
A method for detecting the binary significance of a frequency shift signal having at least a first frequency and a second frequency representative of binary data comprising the steps of: differentiating the frequency shift signal to obtain a differentiated signal representative of the second derivative with respect to time of the frequency shift signal; controlling the gain of at least one of the differentiated signal and the frequency shift signal so that the relative gain of the differentiated signal is proportional to the reciprocal of the square of a frequency intermEdiate the first and second frequencies of the frequency shift signal; inverting one of said differentiated signal and said frequency shift signal; comparing the magnitude of the inverted signal with the other of said signals; indicating the binary significance of the frequency shift signal in accordance with the result of the comparison.
Claim 8
Dependent Claim
51 words
The method for detecting the binary significance of a frequency shift signal as set forth in claim 5 wherein the gain of the differentiated signal is controlled by an amount proportional to the reciprocal of the square of a frequency intermediate the first and second frequencies of the frequency shift signal.
Claim 9
Dependent Claim
33 words
The method for detecting the binary significance of a frequency shift signal set forth in claim 5 wherein said differentiated signal is inverted and compared with the magnitude of the frequency shift signal.
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) | 1975-05-02 | 1975-11-01 | 1976-05-02 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-05-02 | 1979-11-01 | 1980-05-02 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-05-02 | 1983-11-01 | 1984-05-02 | $7700.00 | Window Closed / Lapsed |