Patent USRE19593E successfully refreshed from Google Patents.
Patent US3668289A successfully refreshed from Google Patents.
US3668289A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Key telephone system link switching network
Assignee: AT&T Inc
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Filing: 1970-08-03
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Granted: 1972-06-06
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Expires: 1990-08-03
Abstract
Abstract A conference link for a plurality of telephone station sets is disclosed which eliminates the need for battery feed coils by switching in a current supply transistor respective to each telephone set incident to connecting that set to the link. The current supply transistor is biased for constant current operation to provide an additional increment of constant current for each telephone set communicating over the link.
Inventors
- 👤 Francis Michael Fenton
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 18:16
CPC Classifications
H; H04; H04M; H04M3/00; H04M3/42; H04M3/56
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
115 words
A conference link for a plurality of telephone sets comprising a plurality of telephone sets each having a predetermined impedance, a pair of conductors for conveying intelligence among said telephone sets, a transistor respective to each of said telephone sets, an unregulated current source, means for selectively connecting said telephone sets and said transistor respective to each of said sets in circuit with said current source and said pair of conductors, a source of biasing potential, and means controlled by said connecting means for connecting said source of biasing potential to each of said transistors tO cause said transistor to exhibit an impedance to said conductors substantially higher than said impedance of said telephone sets.
Claim 2
Dependent Claim
115 words
A conference link for a plurality of telephone sets comprising a plurality of telephone sets each having a predetermined impedance, a pair of conductors for conveying intelligence among said telephone sets, a transistor respective to each of said telephone sets, an unregulated current source, means for selectively connecting said telephone sets and said transistor respective to each of said sets in circuit with said current source and said pair of conductors, a source of biasing potential, and means controlled by said connecting means for connecting said source of biasing potential to each of said transistors tO cause said transistor to exhibit an impedance to said conductors substantially higher than said impedance of said telephone sets.
Claim 3
Dependent Claim
101 words
A conference link for a plurality of telephone sets comprising a pair of conductors for conveying intelligence among said telephone sets, a transistor respective to each of said telephone sets, an unregulated current source, a source of biasing potential, first and second switching means associated with each said station, said first switching means being operable to connect said station set to one of said pair of conductors, and said second switching means being operable to connect said transistor respective to said station between one of said pair of conductors and said unregulated current source and to said source of biasing potential.
Claim 4
Dependent Claim
101 words
A conference link for a plurality of telephone sets comprising a pair of conductors for conveying intelligence among said telephone sets, a transistor respective to each of said telephone sets, an unregulated current source, a source of biasing potential, first and second switching means associated with each said station, said first switching means being operable to connect said station set to one of said pair of conductors, and said second switching means being operable to connect said transistor respective to said station between one of said pair of conductors and said unregulated current source and to said source of biasing potential.
Claim 5
Dependent Claim
70 words
A conference link according to claim 2 wherein said source of biasing potential comprises a Zener diode having one end thereof connected to the base of each said respective transistor and wherein said second switching means includes a further transistor respective to each of said telephone sets said further transistor being connected between the other end of said Zener diode and a current carrying electrode of said first-mentioned respective transistor.
Claim 6
Dependent Claim
23 words
A conference link according to claim 3 further comprising diode means connected between said station and the other of said pair of conductors.
Claim 7
Dependent Claim
34 words
A conference link according to claim 4 wherein said Zener diode is connected in circuit with the base emitter junction of said first-mentioned transistor respective to said telephone set by said second switching means.
Claim 8
Dependent Claim
45 words
A conference link according to claim 5 wherein said first switching means includes a transistor and wherein coupling means are provided for connecting one electrode of said transistor of said second switching means to a control electrode of said transistor of said first switching means.
Claim 9
Dependent Claim
95 words
A communications link comprising a pair of communications conductors, a plurality of telephone sets, an unregulated current source, a transistor having base, emitter and collector electrodes individual to each of said station sets, a source of constant bias potential, and switching means individual to each of said telephone sets for connecting the emitter and base electrodes of said respective transistor in circuit with said source of constant bias potential and for connecting the emitter and collector electrodes of said respective transistor in circuit between one of said pair of conductors and said source of current.
Claim 10
Dependent Claim
95 words
A communications link comprising a pair of communications conductors, a plurality of telephone sets, an unregulated current source, a transistor having base, emitter and collector electrodes individual to each of said station sets, a source of constant bias potential, and switching means individual to each of said telephone sets for connecting the emitter and base electrodes of said respective transistor in circuit with said source of constant bias potential and for connecting the emitter and collector electrodes of said respective transistor in circuit between one of said pair of conductors and said source of current.
Claim 11
Dependent Claim
92 words
A line circuit comprising: a first and second conductor, a plurality of station sets connected between said conductors, a respective switching transistor connected between each of said station sets and one of said conductors and operable to deliver current to its associated station set from said conductor, a plurality of constant current sources equal in number to said station sets, and means for operatively connecting in a respective one of said constant current sources to supply an increment of current to said conductors each time one of said switching transistors is operated.
Claim 12
Dependent Claim
92 words
A line circuit comprising: a first and second conductor, a plurality of station sets connected between said conductors, a respective switching transistor connected between each of said station sets and one of said conductors and operable to deliver current to its associated station set from said conductor, a plurality of constant current sources equal in number to said station sets, and means for operatively connecting in a respective one of said constant current sources to supply an increment of current to said conductors each time one of said switching transistors is operated.
Claim 13
Dependent Claim
32 words
A link circuit according to claim 8 wherein each of said constant current sources comprises a transistor having its base emitter junction biased for constant current operation of its emitter collector path.
Claim 14
Dependent Claim
34 words
A link circuit according to claim 9 further including a Zener diode having one terminal thereof connected to bias the base of each of said transistors biased for said constant current mode of operation.
Claim 15
Dependent Claim
31 words
A link according to claim 10 further comprising a third transistor, said respective switching transistor and said respective transistor biased for constant current operation being simultaneously enabled by said third transistor.
Claim 16
Dependent Claim
37 words
A link according to claim 10 further comprising means connecting said third transistor to the base of said respective switching transistor and to the emitter of said respective transistor biased for said constant current mode of operation.
References Cited (Backward Citations)
US3524929A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-06-06 | 1975-12-06 | 1976-06-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-06-06 | 1979-12-06 | 1980-06-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-06-06 | 1983-12-06 | 1984-06-06 | $7700.00 | Window Closed / Lapsed |