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US3671670A
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Digital filter frequency-shift modulator
Assignee: AT&T Inc
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Filing: 1970-04-15
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Granted: 1972-06-20
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Expires: 1990-04-15
Abstract
Abstract Unity gain feedback places a second-order digital filter on the borderline of stability. The filter therefore oscillates in a numerical sense. Two feedback multipliers, each capable of determining a different central coefficient (and thus different oscillation frequencies) are alternatively inserted into an independent feedback path under control of an input baseband data signal whereby the output frequency is shifted in accordance with the input data. Phase discontinuities and amplitude variations due to the frequency shift are eliminated by extracting the numbers stored in the filter when a data transition occurs and reinserting new numbers representing samples of the new frequency wave, the new numbers further defining points on the new wave having the same instantaneous amplitude and phase as the wave samples defined by the extracted numbers.
Inventors
- 👤 Burton R Saltzberg
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 20:25
CPC Classifications
H; H04; H04L; H04L27/00; H04L27/10; H04L27/12
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
128 words
A frequency-shift modulator comprising a digital filter for processing multibit numbers, the digital filter including means for storing the multibit numbers, means for placing the digital filter on the borderline of stability to produce oscillations, and means for changing the filter central coefficient in response to an applied data signal to thereby produce numbers representing the amplitude and phase of points on a frequency shift signal wave, characterized in that means maintain the phase of the signal wave after each frequency shift continuous with the phase of the wave before the frequency shift, comprising means effective during limited intervals defined by the transitions of the data signal for changing the stored multibit numbers to numbers representing points having the same phase but on a wave different in frequency.
Claim 2
Dependent Claim
128 words
A frequency-shift modulator comprising a digital filter for processing multibit numbers, the digital filter including means for storing the multibit numbers, means for placing the digital filter on the borderline of stability to produce oscillations, and means for changing the filter central coefficient in response to an applied data signal to thereby produce numbers representing the amplitude and phase of points on a frequency shift signal wave, characterized in that means maintain the phase of the signal wave after each frequency shift continuous with the phase of the wave before the frequency shift, comprising means effective during limited intervals defined by the transitions of the data signal for changing the stored multibit numbers to numbers representing points having the same phase but on a wave different in frequency.
Claim 3
Dependent Claim
26 words
A frequency-shift modulator in accordance with claim 1 wherein the means for changing the stored multibit numbers obtain new numbers representing points having the same amplitude.
Claim 4
Dependent Claim
81 words
A frequency-shift modulator in accordance with claim 2 wherein the means for changing the stored multibit numbers obtain new numbers defined by the expression: X cos Delta omega T + Square Root A2 - X2 sin Delta omega T where X represents the stored number, Delta omega is the difference between the radian frequencies of the signal waves, A is the amplitude of the signal wave and T is the time interval between successive ones of the points on the wave.
Claim 5
Dependent Claim
80 words
A frequency-shift modulator in accordance with claim 2 wherein the means for changing the stored multibit numbers obtain new numbers defined by the expression: X cos Delta omega T -Square Root A2 - X2 sin Delta omega T where X represents the stored number, Delta omega is the difference between the radian frequencies of the signal waves, A is the amplitude of the signal wave and T is the time interval between successive ones of the points on the wave.
Claim 6
Dependent Claim
141 words
A digital filter frequency-shift modulator for storing and processing multibit numbers including means for changing the filter central coefficient in response to samples of an applied data signal to produce numbers defining the amplitude and phase of successive points on a frequency-shift signal wave and at least two storing means for storing numbers representing two successive points on the wave, charaterized in that, means responsive to a transition of the sampled data signal extract the numbers representing two successive points on the signal wave produced in accordance with the data signal, means process the two extracted numbers to develop a new number defining a point having the same amplitude and phase as the point defined by one of the extracted numbers but on a signal wave different in frequency, and means insert the new number into one of the storing means.
Claim 7
Dependent Claim
141 words
A digital filter frequency-shift modulator for storing and processing multibit numbers including means for changing the filter central coefficient in response to samples of an applied data signal to produce numbers defining the amplitude and phase of successive points on a frequency-shift signal wave and at least two storing means for storing numbers representing two successive points on the wave, charaterized in that, means responsive to a transition of the sampled data signal extract the numbers representing two successive points on the signal wave produced in accordance with the data signal, means process the two extracted numbers to develop a new number defining a point having the same amplitude and phase as the point defined by one of the extracted numbers but on a signal wave different in frequency, and means insert the new number into one of the storing means.
Claim 8
Dependent Claim
29 words
A digital filter frequency-shift modulator in accordance with claim 5 wherein the process means is further responsive to samples of the applied data signal to develop the new number.
Claim 9
Dependent Claim
93 words
A digital filter frequency-shift modulator in accordance with claim 5 wherein the process means is arranged to develop the new number as defined by the expression: where X1 and X2 represent the two extracted numbers, Delta omega is the difference in the radian frequencies of the two signal waves, omega 1 is the frequency of the wave defined by the extracted numbers and T is the time interval between the successive points on the wave and wherein the new number is inserted into the storing means from whence the number X1 is extracted.
Claim 10
Dependent Claim
93 words
A digital filter frequency-shift modulator in accordance with claim 5 wherein the process means is arranged to develop the new number as defined by the expression: where X1 and X2 represent the two extracted numbers, Delta omega is the difference in the radian frequencies of the two signal waves, omega 1 is the frequency of the wave defined by the extracted numbers and T is the time interval between the successive points on the wave and wherein the new number is inserted into the storing means from which the number X2 is extracted.
Claim 11
Independent Claim
104 words
The method of eliminating phase discontinuities in a digital filter frequency-shift modulator which, in response to a binary data signal, stores and processes multibit numbers defining the amplitude and phase of various points on one or the other of two signal waves of different frequencies comprising the steps of; extracting a number stored in the digital filter each time a transition of the binary data signal occurs, generating a new number defining a point having the same phase as the point defined by the extracted number but being on the signal wave different in frequency, and inserting the new number into the digital filter.
Claim 12
Independent Claim
104 words
The method of eliminating phase discontinuities in a digital filter frequency-shift modulator which, in response to a binary data signal, stores and processes multibit numbers defining the amplitude and phase of various points on one or the other of two signal waves of different frequencies comprising the steps of; extracting a number stored in the digital filter each time a transition of the binary data signal occurs, generating a new number defining a point having the same phase as the point defined by the extracted number but being on the signal wave different in frequency, and inserting the new number into the digital filter.
Claim 13
Dependent Claim
38 words
The method of eliminating phase discontinuities in a digital filter frequency-shift modulator in accordance with claim 9 wherein the point defined by the new generated number has the same amplitude as the point defined by the extracted number.
Claim 14
Independent Claim
103 words
The method of eliminating discontinuities in a digital filter frequency-shift modulator which, in response to a binary data signal, stores and processes multibit numbers defining the amplitude and phase of various points on one or the other of two signal waves of different frequencies comprising the steps of; extracting a number stored in the digital filter each time a transition of the binary data signal occurs, generating a new number defining a point having the same amplitude as the point defined by the extracted number but being on the signal wave different in frequency, and inserting the new number into the digital filter.
Claim 15
Independent Claim
103 words
The method of eliminating discontinuities in a digital filter frequency-shift modulator which, in response to a binary data signal, stores and processes multibit numbers defining the amplitude and phase of various points on one or the other of two signal waves of different frequencies comprising the steps of; extracting a number stored in the digital filter each time a transition of the binary data signal occurs, generating a new number defining a point having the same amplitude as the point defined by the extracted number but being on the signal wave different in frequency, and inserting the new number into the digital filter.
References Cited (Backward Citations)
US3551849A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-06-20 | 1975-12-20 | 1976-06-20 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-06-20 | 1979-12-20 | 1980-06-20 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-06-20 | 1983-12-20 | 1984-06-20 | $7700.00 | Window Closed / Lapsed |