US3717754A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Digital filter arrangement which alternatively filters two signals differing in frequency
Assignee: AT&T Inc
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Filing: 1971-05-26
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Granted: 1973-02-20
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Expires: 1991-05-26
Abstract
Abstract A plurality of telephone lines which convey frequency-shift signals and a corresponding plurality of data machines, which send and receive do baseband data are interconnected via a timeshared digital (filter) circuit receiver and digital circuit modulator under the supervision of a common central processor. A low-pass digital filter is arranged to filter the incoming signals to detect ringing or, alternatively, to filter the sum of the signaling frequencies to detect carrier. To detect the low frequency ringing, the response of the filter is modified by limiting the rate at which the input signals are applied thereto and by ''''holding'''' the processed signals in the filter for the prolonged interval between the input signal applications.
Inventors
- 👤 C Buzzard
- 👤 G Pasternack
- 👤 B Saltzberg
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 12:27
CPC Classifications
H; H04; H04Q; H04Q1/00; H04Q1/18; H04Q1/30; H04Q1/44; H04Q1/444; H04Q1/446; H04Q1/448; H03; H03H; H03H17/00; H03H17/02; H03H17/0283; H03H17/0292; H03H2218/00; H03H2218/06
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
127 words
A digital filter for alternatively filtering two signals, one signal which is approximately n times greater in frequency than the other signal and wherein means sample each of the two signals, the sampling means having a sampling rate which is sufficiently high to sample each cycle of the one signal a plurality of times, the digital filter being normally arranged to process signal samples having the sampling rate of the sampling means, characterized in that means are provided for modifying the digital filter to process the other signal, the modifying means including means for applying to the filter one of each n samples of the other signal, and means for interrupting the processing of signal samples during the intervals between the applications of the other signal samples.
Claim 2
Dependent Claim
127 words
A digital filter for alternatively filtering two signals, one signal which is approximately n times greater in frequency than the other signal and wherein means sample each of the two signals, the sampling means having a sampling rate which is sufficiently high to sample each cycle of the one signal a plurality of times, the digital filter being normally arranged to process signal samples having the sampling rate of the sampling means, characterized in that means are provided for modifying the digital filter to process the other signal, the modifying means including means for applying to the filter one of each n samples of the other signal, and means for interrupting the processing of signal samples during the intervals between the applications of the other signal samples.
Claim 3
Dependent Claim
127 words
A digital filter for alternatively filtering two signals, one signal which is approximately n times greater in frequency than the other signal and wherein means sample each of the two signals, the sampling means having a sampling rate which is sufficiently high to sample each cycle of the one signal a plurality of times, the digital filter being normally arranged to process signal samples having the sampling rate of the sampling means, characterized in that means are provided for modifying the digital filter to process the other signal, the modifying means including means for applying to the filter one of each n samples of the other signal, and means for interrupting the processing of signal samples during the intervals between the applications of the other signal samples.
Claim 4
Dependent Claim
127 words
A digital filter for alternatively filtering two signals, one signal which is approximately n times greater in frequency than the other signal and wherein means sample each of the two signals, the sampling means having a sampling rate which is sufficiently high to sample each cycle of the one signal a plurality of times, the digital filter being normally arranged to process signal samples having the sampling rate of the sampling means, characterized in that means are provided for modifying the digital filter to process the other signal, the modifying means including means for applying to the filter one of each n samples of the other signal, and means for interrupting the processing of signal samples during the intervals between the applications of the other signal samples.
Claim 5
Dependent Claim
50 words
A digital filter in accordance with claim 2, wherein the filter comprises a recursive filter having a feedback path for combining processed signal samples with applied signal samples and the interrupting means includes means for blocking the feedback path during the intervals between the applications of the other signal samples.
References Cited (Backward Citations)
US3531727A
Cited
US3621402A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-02-20 | 1976-08-21 | 1977-02-20 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-02-20 | 1980-08-21 | 1981-02-20 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-02-20 | 1984-08-21 | 1985-02-20 | $7700.00 | Window Closed / Lapsed |