Patent US3855537A successfully refreshed from Google Patents.
US3855537A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Band-separation filter with reduced path cross-connections
Assignee: AT&T Inc
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Filing: 1973-08-09
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Granted: 1974-12-17
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Expires: 1993-08-09
Abstract
Abstract Plural bandpass filter units in a band-separation filter (BSF) are supplied with a common input signal and have passband characteristics for dividing that signal into different predetermined frequency bands on respective circuits. Frequency selective degenerative feedback is employed within each filter branch circuit, in combination with broadband degenerative feedback from all branch circuit outputs to the common input, for suppressing in each branch the signal effects corresponding to frequency bands of other branches. In addition, the degenerated common input signal has a multinotch frequency spectrum with a notch at each branch frequency. A first BSF is used in the multinotch mode to block, e.g., telephone dial tone frequencies and thereby facilitate the operation of a tandem second BSF operating in the BSF mode to select pushbutton dialing frequencies.
Inventors
- 👤 J Condon
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 22:32
CPC Classifications
H; H04; H04Q; H04Q1/00; H04Q1/18; H04Q1/30; H04Q1/44; H04Q1/444; H04Q1/45; H04Q1/457
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
91 words
An electrical frequency filter apparatus comprising a plurality of bandpass frequency filter units covering different frequency bands and connected to be fed electrical signals from a common input connection, means, in each filter unit, for degeneratively feeding back an output of such unit to an input thereof for all but a different one of said bands, and means for degeneratively feeding back outputs of all of said units back to said common input connection to effect substantially complete cancellation of said different bands in such input for producing a degenerated input.
Claim 2
Dependent Claim
91 words
An electrical frequency filter apparatus comprising a plurality of bandpass frequency filter units covering different frequency bands and connected to be fed electrical signals from a common input connection, means, in each filter unit, for degeneratively feeding back an output of such unit to an input thereof for all but a different one of said bands, and means for degeneratively feeding back outputs of all of said units back to said common input connection to effect substantially complete cancellation of said different bands in such input for producing a degenerated input.
Claim 3
Dependent Claim
63 words
The filter apparatus in accordance with claim 1 in which each filter unit comprises a series signal transmission path, an operational amplifier connected in series in said path, and a circuit tuned for minimum current transmission at the center frequency of the filter unit passband and connected between the amplifier output and an input of the amplifier in the unit series signal path.
Claim 4
Dependent Claim
62 words
The filter apparatus in accordance with claim 1 wherein each filter unit comprises an operational amplifier, a commutatable capacitor impedance unit connected between an output of the amplifier and an inverting input thereof, and means for supplying to said cOmmutatable capacitor unit a drive signal for controlling capacitor commutation therein at the frequency of the center of the passband for such unit.
Claim 5
Dependent Claim
48 words
The filter in accordance with claim 1 in which said degenerative feedback means to said common input connection comprise leads extending alaong nonintersecting paths from respective outputs of said units to said common input connection, each of said leads having a bandpass response including all of said bands.
Claim 6
Dependent Claim
45 words
The filter in accordance with claim 4 in which said filter is a substantially planar circuit array, each of said filter units connected to said common input connection comprises a different filter branch circuit, and said lead paths further lack intersections with said branch circuits.
Claim 7
Dependent Claim
85 words
The filter in accordance with claim 1 in which said degenerative feedback means to said common input connection comprises an electrical circuit summing node, connections thereto from said common input and from an output of each of said filter units, and connections from said node to inputs of each of said filter units, and an output connection is provided from said node for presenting a node signal having an multinotch band rejection frequency spectrum characteristic, notches of said characteristic being at said different frequecy bands.
Claim 8
Dependent Claim
87 words
The filter in accordance with claim 6 in which said filter units, degenerative feedback means, and node output connection comprise a first filter, a second filter is provided which also includes a common input connection, plural filter units and degenerative feedback means therefor connected as aforesaid for said first filter, means are provided for connecting said node output connection of said first filter to said common input connection of said second filter, and filter units of said first and second filters are all tuned to different frequencies.
Claim 9
Dependent Claim
53 words
The filter in accordance with claim 7 in which said degenerative feedback means of each filter unit comprises a different commutatable capacitor impedance unit, and means are provided for applying to each of said impedance units a drive signal for controlling capacitor commutation therein at a frequency of the passband for such unit.
Claim 10
Dependent Claim
47 words
The filter in accordance with claim 7 in which utilization means, responsive to outputs of said units of said second filter, are provided, and means are provided for inhibiting operation of said utilization means in response to signals at said common input connection of said second filter.
Claim 11
Dependent Claim
62 words
In a multiple frequency band-separation filter incorporating a plurality of active bandpass filters each connected between a common input node and a different output node, the improvement comprising: a plurality of electrical circuits each connecting a different output node to said common input node and providing degenerative feedback thereto, said circuits including no elements in common with any of said bandpass filters.
Claim 12
Dependent Claim
62 words
In a multiple frequency band-separation filter incorporating a plurality of active bandpass filters each connected between a common input node and a different output node, the improvement comprising: a plurality of electrical circuits each connecting a different output node to said common input node and providing degenerative feedback thereto, said circuits including no elements in common with any of said bandpass filters.
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) | 1977-12-16 | 1978-06-17 | 1978-12-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-12-16 | 1982-06-17 | 1982-12-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-12-16 | 1986-06-17 | 1986-12-17 | $7700.00 | Window Closed / Lapsed |