US3890577A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Vital active low-pass filter
Assignee: Trane US Inc
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Filing: 1973-08-15
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Granted: 1975-06-17
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Expires: 1993-08-15
Abstract
Abstract This invention relates to a fail-safe variable type of low-pass filtering circuit. The filtering circuit includes a passive R-C network and an active semiconductive amplifying stage. The upper transmission frequency of a.c. input signals is varied by changing the resistance of the R-C network.
Inventors
- 👤 Reed H Grundy
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 11:24
CPC Classifications
H; H03; H03H; H03H11/00; H03H11/02; H03H11/04; H03H11/12; H03H11/1213; B; B61; B61L; B61L3/00; G; G01; G01P; G01P1/00; G01P1/07; G01P1/08; G01P1/10; G01P1/103; G01P3/00; G01P3/42; G01P3/44; G01P3/48; G01P3/4802
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
74 words
A vital signal frequency filtering circuit comprising, a source of a.c. signals, a fail-safe variable passive R-C network having a plurality of individual resistors and a four-terminal capacitor coupled to said source of a.c. signals, and an active amplifying circuit having its input supplied by said fail-safe passive R-C network and having its output developing a range of frequencies which is dependent upon the resistance and capacitance values of said fail-safe passive R-C network.
Claim 2
Dependent Claim
74 words
A vital signal frequency filtering circuit comprising, a source of a.c. signals, a fail-safe variable passive R-C network having a plurality of individual resistors and a four-terminal capacitor coupled to said source of a.c. signals, and an active amplifying circuit having its input supplied by said fail-safe passive R-C network and having its output developing a range of frequencies which is dependent upon the resistance and capacitance values of said fail-safe passive R-C network.
Claim 3
Dependent Claim
23 words
A vital signal frequency filtering circuit as defined in claim 1, wherein said fail safe variable passive R-C network is a low-pass filter.
Claim 4
Dependent Claim
32 words
A vital signal frequency filtering circuit as defined in claim 1, wherein the resistance value of said fail safe passive R-C network is varied in order to change the range of frequencies.
Claim 5
Dependent Claim
50 words
A vital signal frequency filtering circuit as defined in claim 1, wherein said four-terminal capacitor of said fail-safe passive R-C network has a first pair of terminals coupled to said source of a.c. signals and has a second pair of terminals coupled to the input of said active amplifier circuit.
Claim 6
Dependent Claim
20 words
A vital signal frequency filtering circuit as defined in claim 1, wherein said active amplifying circuit includes a semiconductive device.
Claim 7
Dependent Claim
19 words
A vital signal frequency filtering circuit as defined in claim 5, wherein said semiconductive device is an NPN transistor.
Claim 8
Dependent Claim
25 words
A vital signal frequency filtering circuit as defined in claim 1, wherein said active amplifying circuit includes a transistor connected in a common emitter configuration.
Claim 9
Dependent Claim
27 words
A vital signal frequency filtering citcuit as defined in claim 7, wherein a voltage divider includes a pair of series connected resistors for forwardly biasing said transistor.
Claim 10
Dependent Claim
32 words
A vital signal frequency filtering circuit as defined in claim 1, wherein a coupling capacitor is interconnected between said fail sAfe passive R-C network and the input of said active amplifying circuit.
Claim 11
Dependent Claim
81 words
A vital signal frequency filtering circuit as defined in claim 6, wherein the emitter electrode of said NPN transistor is connected to ground via an emitter load resistor, the collector electrode of said NPN transistor is connected to a positive d.c. supply terminal via a collector load resistor, and the base electrode of said NPN transistor is connected to the junction of a voltage dividing network which includes a pair of resistors connected between ground and the positive d.c. supply terminal.
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) | 1978-06-16 | 1978-12-16 | 1979-06-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-06-16 | 1982-12-16 | 1983-06-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-06-16 | 1986-12-16 | 1987-06-17 | $7700.00 | Window Closed / Lapsed |