US5694466A
Expired / Lapsed
US
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DTMF detector system and method which performs improved twist computation and thresholding
Assignee: Microsemi Semiconductor US Inc
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Filing: 1996-01-18
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Granted: 1997-12-02
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Expires: 2016-01-18
Abstract
Abstract An improved dual tone multifrequency (DTMF) or multitone signal detector which more efficiently and reliably detects DTMF signals. The present invention performs twist computations only when the signal has become stable, thus achieving more accuracy and reliability. The DTMF detector receives a plurality of digital samples of a received signal and calculates energy values for each of the plurality of different uncorrelated frequencies. The DSP then determines maximum values of the energy values for each of the two or more frequency groups, referred to as M(1) and M(2), to detect the plurality of tones in the received signal. The DTMF detector then performs improved twist computation and thresholding. The DTMF detector first determines if the M(1) and M(2) values of the respective frame being examined have the same indices. If so, the DTMF detector compares each of the M(1) and M(2) values of the respective frame being examined with the M(1) and M(2) values of the immediately prior frame, referred to as M'(1) and M'(2), and determines if the M(1) and M(2) values of the current frame are greater than the M'(1) and M'(2) values of the prior frame. If the M(1) and M(2) values of the current frame are greater than the M'(1) and M'(2) values of the prior frame, then the DTMF detector calculates a twist value using the maximum energy values M(1) and M(2) for the current frame being examined.
Inventors
- 👤 Zheng-yi Xie
- 👤 John G. Bartkowiak
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 09:50
CPC Classifications
H; H04; H04Q; H04Q1/00; H04Q1/18; H04Q1/30; H04Q1/44; H04Q1/444; H04Q1/45; H04Q1/453; H04Q1/457; H04M; H04M7/00; H04M7/12; H04M7/1205; H04M7/1295
Claims Analysis
Total Claims: 35
Claim 1
Independent Claim
217 words
A method for detecting dual tone multifrequency (DTMF) signals with improved twist computation and thresholding, comprising: receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise two or more frequency groups; determining energy values for each of said different uncorrelated frequencies comprising said two or more frequency groups for a first frame; determining a maximum energy value among said energy values for said different uncorrelated frequencies for each of said two or more frequency groups for said first frame; comparing each of said maximum energy values for said first frame with respective maximum energy values from a prior frame; determining if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame; and calculating a twist value using said maximum energy values for each of said two or more frequency groups for said first frame if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame.
Claim 2
Independent Claim
217 words
A method for detecting dual tone multifrequency (DTMF) signals with improved twist computation and thresholding, comprising: receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise two or more frequency groups; determining energy values for each of said different uncorrelated frequencies comprising said two or more frequency groups for a first frame; determining a maximum energy value among said energy values for said different uncorrelated frequencies for each of said two or more frequency groups for said first frame; comparing each of said maximum energy values for said first frame with respective maximum energy values from a prior frame; determining if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame; and calculating a twist value using said maximum energy values for each of said two or more frequency groups for said first frame if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame.
Claim 3
Dependent Claim
57 words
The method of claim 1, further comprising: setting said twist value for said first frame equal to a twist value for said prior frame if said maximum energy values for at least one of said two or more frequency groups for said first frame are not greater than said respective maximum energy values from said prior frame.
Claim 4
Dependent Claim
52 words
The method of claim 1, further comprising: comparing said twist value with one or more threshold values to determine if said twist value is within an acceptable range; and detecting said plurality of tones in said received signal only if said determining determines that said twist value is within said acceptable range.
Claim 5
Dependent Claim
25 words
The method of claim 3, further comprising: setting a twist error if said determining determines that said twist value is not within said acceptable range.
Claim 6
Dependent Claim
141 words
The method of claim 1, wherein said maximum energy values among said energy values for said different uncorrelated frequencies for said first frame are each associated with a respective one of said different uncorrelated frequencies; the method further comprising: determining if said maximum energy values for said prior frame are associated with said respective ones of said different uncorrelated frequencies; performing said comparing each of said maximum energy values for said first frame with respective maximum energy values from a prior frame, said determining if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame, and said calculating a twist value, only if said maximum energy values for said prior frame are associated with said respective ones of said different uncorrelated frequencies.
Claim 7
Dependent Claim
152 words
The method of claim 1, wherein each of said energy values for said different uncorrelated frequencies have unique index values corresponding to one of said different uncorrelated frequencies; wherein said maximum energy values for said first frame each have a respective index; the method further comprising: determining if said maximum energy values for said prior frame have the same indices as said maximum energy values for said first frame; performing said comparing each of said maximum energy values for said first frame with respective maximum energy values from a prior frame, said determining if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame, and said calculating a twist value, only if said maximum energy values for said prior frame have the same indices as said maximum energy values for said first frame.
Claim 8
Dependent Claim
18 words
The method of claim 1, wherein said prior frame is the immediately prior frame of said first frame.
Claim 9
Dependent Claim
114 words
The method of claim 1, wherein said plurality of different uncorrelated frequencies comprise only two frequency groups, wherein said two frequency groups consist of a first frequency group and a second frequency group; wherein said determining a maximum energy value among said energy values for said different uncorrelated frequencies for each of said two or more frequency groups for said first frame comprises determining a maximum energy value for said first frequency group and determining a maximum energy value for said second frequency group; wherein said calculating a twist value includes calculating a ratio of said maximum energy value for said second frequency group to said maximum energy value for said first frequency group.
Claim 10
Independent Claim
215 words
A method for detecting dual tone multifrequency (DTMF) signals with improved twist computation and thresholding, comprising: receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise two or more frequency groups; determining energy values for each of said different uncorrelated frequencies comprising said two or more frequency groups for a first frame; determining a maximum energy value among said energy values for said different uncorrelated frequencies for each of said two or more frequency groups for said first frame; comparing each of said maximum energy values for said first frame with respective maximum energy values from a prior frame; determining if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame; and setting said twist value for said first frame equal to a twist value for said prior frame if said maximum energy values for at least one of said two or more frequency groups for said first frame are not greater than said respective maximum energy values from said prior frame.
Claim 11
Independent Claim
215 words
A method for detecting dual tone multifrequency (DTMF) signals with improved twist computation and thresholding, comprising: receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise two or more frequency groups; determining energy values for each of said different uncorrelated frequencies comprising said two or more frequency groups for a first frame; determining a maximum energy value among said energy values for said different uncorrelated frequencies for each of said two or more frequency groups for said first frame; comparing each of said maximum energy values for said first frame with respective maximum energy values from a prior frame; determining if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame; and setting said twist value for said first frame equal to a twist value for said prior frame if said maximum energy values for at least one of said two or more frequency groups for said first frame are not greater than said respective maximum energy values from said prior frame.
Claim 12
Dependent Claim
59 words
The method of claim 9, further comprising: calculating a twist value using said maximum energy values for each of said two or more frequency groups for said first frame if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame.
Claim 13
Dependent Claim
256 words
A dual tone multifrequency detector for detecting dual tone multifrequency (DTMF) signals, comprising: means for receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise two or more frequency groups; a digital signal processor for calculating a frequency spectrum on said plurality of digital samples for each of said plurality of different uncorrelated frequencies, wherein said digital signal processor determines energy values for each of said different uncorrelated frequencies comprising said two or more frequency groups for a first frame; wherein said digital signal processor determines a maximum energy value among said different uncorrelated frequencies for each of said two or more frequency groups for said first frame and compares each of said maximum energy values for said first frame with respective maximum energy values from a prior frame; wherein said digital signal processor determines if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame; wherein said digital signal processor calculates a twist value using said maximum energy values for each of said two or more frequency groups for said first frame if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame.
Claim 14
Dependent Claim
256 words
A dual tone multifrequency detector for detecting dual tone multifrequency (DTMF) signals, comprising: means for receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise two or more frequency groups; a digital signal processor for calculating a frequency spectrum on said plurality of digital samples for each of said plurality of different uncorrelated frequencies, wherein said digital signal processor determines energy values for each of said different uncorrelated frequencies comprising said two or more frequency groups for a first frame; wherein said digital signal processor determines a maximum energy value among said different uncorrelated frequencies for each of said two or more frequency groups for said first frame and compares each of said maximum energy values for said first frame with respective maximum energy values from a prior frame; wherein said digital signal processor determines if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame; wherein said digital signal processor calculates a twist value using said maximum energy values for each of said two or more frequency groups for said first frame if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame.
Claim 15
Dependent Claim
63 words
The dual tone multifrequency detector of claim 11, wherein said digital signal processor sets said twist value for said first frame equal to a twist value for said prior frame if said maximum energy values for at least one of said two or more frequency groups for said first frame are not greater than said respective maximum energy values from said prior frame.
Claim 16
Dependent Claim
66 words
The dual tone multifrequency detector of claim 11, wherein said digital signal processor compares said twist value with one or more threshold values to determine if said twist value is within an acceptable range; and wherein said dual tone multifrequency detector detects said plurality of tones in said received signal only if said digital signal processor determines that said twist value is within said acceptable range.
Claim 17
Dependent Claim
27 words
The dual tone multifrequency detector of claim 13, wherein said digital signal processor sets a twist error if said twist value is not within said acceptable range.
Claim 18
Dependent Claim
145 words
The dual tone multifrequency detector of claim 11, wherein said maximum energy values among said energy values for said different uncorrelated frequencies for said first frame are each associated with a respective one of said different uncorrelated frequencies; wherein said digital signal processor determines if said maximum energy values for said prior frame are associated with said respective ones of said different uncorrelated frequencies; performing said comparing each of said maximum energy values for said first frame with respective maximum energy values from a prior frame, said determining if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame, and said calculating a twist value, only if said maximum energy values for said prior frame are associated with said respective ones of said different uncorrelated frequencies.
Claim 19
Dependent Claim
155 words
The dual tone multifrequency detector of claim 11, wherein each of said energy values for said different uncorrelated frequencies have unique index values corresponding to one of said different uncorrelated frequencies; wherein said maximum energy values for said first frame each have a respective index; the method further comprising: determining if said maximum energy values for said prior frame have the same indices as said maximum energy values for said first frame; performing said comparing each of said maximum energy values for said first frame with respective maximum energy values from a prior frame, said determining if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame, and said calculating a twist value, only if said maximum energy values for said prior frame have the same indices as said maximum energy values for said first frame.
Claim 20
Dependent Claim
21 words
The dual tone multifrequency detector of claim 11, wherein said prior frame is the immediately prior frame of said first frame.
Claim 21
Dependent Claim
117 words
The dual tone multifrequency detector of claim 11, wherein said plurality of different uncorrelated frequencies comprise only two frequency groups, wherein said two frequency groups consist of a first frequency group and a second frequency group; wherein said determining a maximum energy value among said energy values for said different uncorrelated frequencies for each of said two or more frequency groups for said first frame comprises determining a maximum energy value for said first frequency group and determining a maximum energy value for said second frequency group; wherein said calculating a twist value includes calculating a ratio of said maximum energy value for said first frequency group and said maximum energy value for said second frequency group.
Claim 22
Dependent Claim
254 words
A dual tone multifrequency detector for detecting dual tone multifrequency (DTMF) signals, comprising: means for receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise two or more frequency groups; a digital signal processor for calculating a frequency spectrum on said plurality of digital samples for each of said plurality of different uncorrelated frequencies, wherein said digital signal processor determines energy values for each of said different uncorrelated frequencies comprising said two or more frequency groups for a first frame; wherein said digital signal processor determines a maximum energy value among said different uncorrelated frequencies for each of said two or more frequency groups for said first frame and compares each of said maximum energy values for said first frame with respective maximum energy values from a prior frame; wherein said digital signal processor determines if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame; wherein said digital signal processor sets said twist value for said first frame equal to a twist value for said prior frame if said maximum energy values for at least one of said two or more frequency groups for said first frame are not greater than said respective maximum energy values from said prior frame.
Claim 23
Dependent Claim
254 words
A dual tone multifrequency detector for detecting dual tone multifrequency (DTMF) signals, comprising: means for receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise two or more frequency groups; a digital signal processor for calculating a frequency spectrum on said plurality of digital samples for each of said plurality of different uncorrelated frequencies, wherein said digital signal processor determines energy values for each of said different uncorrelated frequencies comprising said two or more frequency groups for a first frame; wherein said digital signal processor determines a maximum energy value among said different uncorrelated frequencies for each of said two or more frequency groups for said first frame and compares each of said maximum energy values for said first frame with respective maximum energy values from a prior frame; wherein said digital signal processor determines if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame; wherein said digital signal processor sets said twist value for said first frame equal to a twist value for said prior frame if said maximum energy values for at least one of said two or more frequency groups for said first frame are not greater than said respective maximum energy values from said prior frame.
Claim 24
Dependent Claim
65 words
The dual tone multifrequency detector of claim 19, wherein said digital signal processor calculates a twist value using said maximum energy values for each of said two or more frequency groups for said first frame if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame.
Claim 25
Independent Claim
211 words
A method for detecting multi tone multifrequency (MTMF) signals, comprising: receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise one or more frequency groups; determining energy values for each of said different uncorrelated frequencies comprising said one or more frequency groups for a first frame; determining a maximum energy value among said energy values for said different uncorrelated frequencies for each of said one or more frequency groups for said first frame; comparing each of said maximum energy values for said first frame with respective maximum energy values from a prior frame; determining if said maximum energy values for each of said one or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame; and calculating a twist value using said maximum energy values for each of said one or more frequency groups for said first frame if said maximum energy values for each of said one or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame.
Claim 26
Independent Claim
211 words
A method for detecting multi tone multifrequency (MTMF) signals, comprising: receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise one or more frequency groups; determining energy values for each of said different uncorrelated frequencies comprising said one or more frequency groups for a first frame; determining a maximum energy value among said energy values for said different uncorrelated frequencies for each of said one or more frequency groups for said first frame; comparing each of said maximum energy values for said first frame with respective maximum energy values from a prior frame; determining if said maximum energy values for each of said one or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame; and calculating a twist value using said maximum energy values for each of said one or more frequency groups for said first frame if said maximum energy values for each of said one or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame.
Claim 27
Dependent Claim
57 words
The method of claim 21, further comprising: setting said twist value for said first frame equal to a twist value for said prior frame if said maximum energy values for at least one of said one or more frequency groups for said first frame are not greater than said respective maximum energy values from said prior frame.
Claim 28
Dependent Claim
52 words
The method of claim 21, further comprising: comparing said twist value with one or more threshold values to determine if said twist value is within an acceptable range; and detecting said plurality of tones in said received signal only if said determining determines that said twist value is within said acceptable range.
Claim 29
Dependent Claim
25 words
The method of claim 23, further comprising: setting a twist error if said determining determines that said twist value is not within said acceptable range.
Claim 30
Dependent Claim
141 words
The method of claim 21, wherein said maximum energy values among said energy values for said different uncorrelated frequencies for said first frame are each associated with a respective one of said different uncorrelated frequencies; the method further comprising: determining if said maximum energy values for said prior frame are associated with said respective ones of said different uncorrelated frequencies; performing said comparing each of said maximum energy values for said first frame with respective maximum energy values from a prior frame, said determining if said maximum energy values for each of said one or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame, and said calculating a twist value, only if said maximum energy values for said prior frame are associated with said respective ones of said different uncorrelated frequencies.
Claim 31
Dependent Claim
152 words
The method of claim 21, wherein each of said energy values for said different uncorrelated frequencies have unique index values corresponding to one of said different uncorrelated frequencies; wherein said maximum energy values for said first frame each have a respective index; the method further comprising: determining if said maximum energy values for said prior frame have the same indices as said maximum energy values for said first frame; performing said comparing each of said maximum energy values for said first frame with respective maximum energy values from a prior frame, said determining if said maximum energy values for each of said two or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame, and said calculating a twist value, only if said maximum energy values for said prior frame have the same indices as said maximum energy values for said first frame.
Claim 32
Dependent Claim
18 words
The method of claim 21, wherein said prior frame is the immediately prior frame of said first frame.
Claim 33
Dependent Claim
252 words
A multi tone multifrequency detector for detecting multi tone multifrequency (MTMF) signals, comprising: means for receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise one or more frequency groups; a digital signal processor for calculating a frequency spectrum on said plurality of digital samples for each of said plurality of different uncorrelated frequencies, wherein said digital signal processor determines energy values for each of said different uncorrelated frequencies comprising said one or more frequency groups; wherein said digital signal processor determines a maximum energy value among said different uncorrelated frequencies for each of said one or more frequency groups for said first frame and compares each of said maximum energy values for said first frame with respective maximum energy values from a prior frame; wherein said digital signal processor determines if said maximum energy values for each of said one or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame; wherein said digital signal processor calculates a twist value using said maximum energy values for each of said one or more frequency groups for said first frame if said maximum energy values for each of said one or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame.
Claim 34
Dependent Claim
252 words
A multi tone multifrequency detector for detecting multi tone multifrequency (MTMF) signals, comprising: means for receiving a plurality of digital samples of a received signal, wherein said received signal includes a plurality of tones, wherein said plurality of tones comprise two or more tones from a plurality of different uncorrelated frequencies, wherein said plurality of different uncorrelated frequencies comprise one or more frequency groups; a digital signal processor for calculating a frequency spectrum on said plurality of digital samples for each of said plurality of different uncorrelated frequencies, wherein said digital signal processor determines energy values for each of said different uncorrelated frequencies comprising said one or more frequency groups; wherein said digital signal processor determines a maximum energy value among said different uncorrelated frequencies for each of said one or more frequency groups for said first frame and compares each of said maximum energy values for said first frame with respective maximum energy values from a prior frame; wherein said digital signal processor determines if said maximum energy values for each of said one or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame; wherein said digital signal processor calculates a twist value using said maximum energy values for each of said one or more frequency groups for said first frame if said maximum energy values for each of said one or more frequency groups for said first frame are greater than said respective maximum energy values from said prior frame.
Claim 35
Dependent Claim
63 words
The multi tone multifrequency detector of claim 28, wherein said digital signal processor sets said twist value for said first frame equal to a twist value for said prior frame if said maximum energy values for at least one of said one or more frequency groups for said first frame are not greater than said respective maximum energy values from said prior frame.
References Cited (Backward Citations)
US4853958A
Cited
US5257309A
Cited
US5353345A
Cited
US5325427A
Cited
US5319703A
Cited
US5426696A
Cited
US5428680A
Cited
US5495526A
Cited
US5408529A
Cited
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