US3840710A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Key telephone line circuit
Assignee: AT&T Inc
•
Filing: 1973-05-21
•
Granted: 1974-10-08
•
Expires: 1993-05-21
Abstract
Abstract A key telephone line circuit is disclosed having improved hold control features. The improved circuit is balanced against longitudinal-to-metallic noise conversion by an arrangement which divides the hold impedance equally between both conductors of the central office or PBX line, while still maintaining the line relay operable for detecting loop current. The new arrangement also contains a delay timer for maintaining the hold bridge operated during inadvertent central office loop open conditions. Circuitry is provided for immediately releasing the hold bridge when the subscriber returns from a held condition.
Inventors
- 👤 A Limiero
- 👤 J Smith
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 03:03
CPC Classifications
H; H04; H04M; H04M9/00; H04M9/002; H04M9/005; H04M9/006
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
285 words
A line circuit for use in a key telephone system, said line circuit adapted for connection between a subscriber station and a two-conductor line from a switching network, and adapted for providing loop current flow on said line when said associated subscriber station is in the hold condition, said line circuit comprising a first input pair of terminals for connecting said line circuit to said subscriber station, a second input pair of terminals for connecting said line circuit to each conductor of said line from said switching network, hold control means operable in response to a first signal from said subscriber station for placing an impedance across said second input pair of terminals so as to enable said loop current flow between said conductors of said associated line when said hold control means has been enabled, said hold control means balanced against longitudinal-tometallic noise conversion and comprising a relay having at least one winding, said winding having a first terminal connected to one of said terminals of said second pair of terminals and said relay winding having an impedance of value n, a first resistor having resistance n1, means for connecting said first resistor in parallel with said relay winding when said hold control means has been enabled, a second resistor having resistance n2, said resistor having one terminal connected to said other terminal of said second pair of terminals, a third resistor having resistance n3, means for connecting said third resistor to a second terminal of said relay winding when said hold control means has been enabled, and means for connecting a second terminal of said third resistor to a second terminal of said second resistor when said hold control means has been enabled.
Claim 2
Dependent Claim
285 words
A line circuit for use in a key telephone system, said line circuit adapted for connection between a subscriber station and a two-conductor line from a switching network, and adapted for providing loop current flow on said line when said associated subscriber station is in the hold condition, said line circuit comprising a first input pair of terminals for connecting said line circuit to said subscriber station, a second input pair of terminals for connecting said line circuit to each conductor of said line from said switching network, hold control means operable in response to a first signal from said subscriber station for placing an impedance across said second input pair of terminals so as to enable said loop current flow between said conductors of said associated line when said hold control means has been enabled, said hold control means balanced against longitudinal-tometallic noise conversion and comprising a relay having at least one winding, said winding having a first terminal connected to one of said terminals of said second pair of terminals and said relay winding having an impedance of value n, a first resistor having resistance n1, means for connecting said first resistor in parallel with said relay winding when said hold control means has been enabled, a second resistor having resistance n2, said resistor having one terminal connected to said other terminal of said second pair of terminals, a third resistor having resistance n3, means for connecting said third resistor to a second terminal of said relay winding when said hold control means has been enabled, and means for connecting a second terminal of said third resistor to a second terminal of said second resistor when said hold control means has been enabled.
Claim 3
Dependent Claim
19 words
The invention set forth in claim 1 wherein said resistors have the relationship n.n1 /n+ n1 equals approximately n2.
Claim 4
Dependent Claim
25 words
The invention set forth in claim 1 wherein said resistors have the further relationship n.n1 /n+ n1 + n2 + n3 equals approximately 200 ohms.
Claim 5
Dependent Claim
103 words
The invention set forth in claim 1 further comprising means for removing said hold condition from said line, said hold condition removing means comprising means including said relay for detecting the presence or absence of loop current flowing in a line on hold, means for establishing a timed interval, means responsive to a release of said relay upon a detected absence of loop current when said line circuit is in said hold condition for enabling said timed interval means, and means responsive to the termination of said timed interval and controlled by said timed interval establishing means for releasing said hold control means.
Claim 6
Dependent Claim
56 words
The invention set forth in claim 4 wherein said hold condition removing means further comprises means controllable by said station for releasing said relay, and means responsive to the release of said relay under control of said station controllable means when said line circuit is in said hold condition for immediately releasing said hold control means.
Claim 7
Dependent Claim
212 words
A line cicuit for use in a key telephone system, said line circuit adapted for connection between a subscriber station and a two-conductor line from a switching network, and adapted for maintaining loop current flow on said line when said associated subscriber station is in the hold condition, said line circuit comprising hold control means operable in response to a signal from said subscriber station for placing a hold bridge across said switching network line, said hold control means including a relay having one winding thereof connected in one of said line conductors, said relay adapted for operation when said loop current is flowing between said conductors and for releasing when said loop current stops flowing between said conductors, and said relay having an impedance n, a first impedance having an impedance value n1, means for connecting said first impedance in parallel with said relay winding when said hold control means has been enabled, a second impedance having an impedance value n2, means for connecting said second impedance between said switching network conductors when said hold control means has been enabled, a third impedance having an impedance value n3, and means for connecting said third impedance in said other of said switching network conductors when said hold control means has been enabled.
Claim 8
Dependent Claim
212 words
A line cicuit for use in a key telephone system, said line circuit adapted for connection between a subscriber station and a two-conductor line from a switching network, and adapted for maintaining loop current flow on said line when said associated subscriber station is in the hold condition, said line circuit comprising hold control means operable in response to a signal from said subscriber station for placing a hold bridge across said switching network line, said hold control means including a relay having one winding thereof connected in one of said line conductors, said relay adapted for operation when said loop current is flowing between said conductors and for releasing when said loop current stops flowing between said conductors, and said relay having an impedance n, a first impedance having an impedance value n1, means for connecting said first impedance in parallel with said relay winding when said hold control means has been enabled, a second impedance having an impedance value n2, means for connecting said second impedance between said switching network conductors when said hold control means has been enabled, a third impedance having an impedance value n3, and means for connecting said third impedance in said other of said switching network conductors when said hold control means has been enabled.
Claim 9
Dependent Claim
17 words
The invention set forth in claim 6 wherein said impedances have the relationship n.n1/n+n1 equals approximately n2.
Claim 10
Dependent Claim
23 words
The invention set forth in claim 6 wherein said impedances have the further relationship n.n1/n+n1 + n2 + n3 equals approximately 200 ohms.
Claim 11
Dependent Claim
103 words
The invention set forth in claim 6 further comprising means for removing said hold condition from said line, said hold condition removing means comprising means including said relay for detecting the presence or absence of loop current flowing in a line on hold, means for establishing a timed interval, means responsive to a release of said relay upon a detected absence of loop current when said line circuit is in said hold condition for enabling said timed interval means, and means responsive to the termination of said timed interval and controlled by said timed interval establishing means for releasing said hold control means.
Claim 12
Dependent Claim
56 words
The invention set forth in claim 6 wherein said hold condition removing means further comprises means controllable by said station for releasing said relay, and means responsive to the release of said relay under control of said station controllable means when said line circuit is in said hold condition for immediately releasing said hold control means.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-10-07 | 1978-04-08 | 1978-10-08 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-10-07 | 1982-04-08 | 1982-10-08 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-10-07 | 1986-04-08 | 1986-10-08 | $7700.00 | Window Closed / Lapsed |