US3887774A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Transistor switching circuit for use in a telephone system
Assignee: NEC Platforms Ltd
•
Filing: 1973-03-14
•
Granted: 1975-06-03
•
Expires: 1993-03-14
Abstract
Abstract A D.C. transistor switching circuit is disclosed in which the switching characteristics of the circuit permit two independent signals to be transmitted, in opposite directions to each other over a single conductor, to control two different independent functions between two locations. The switching circuit, comprised of a diode and two transistors connected in opposition to each other, is used in the preferred embodiment in an intercom signalling circuit of a key telephone system to operate a call relay at a called key telephone in response to a signal from a key service unit and, independently of this signal and relay operation, to transmit a busy signal over the same conductor from the key telephone to a lamp on a busy indication lamp field, in order to indicate by illuminating the lamp when the key telephone is busy.
Inventors
- 👤 Hachiroh Takubo
- 👤 Kengo Sudoh
- 👤 Stephen Kerman
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 08:57
CPC Classifications
H; H04; H04M; H04M9/00; H04M9/002; H04M9/003
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
181 words
A switching circuit comprising a semiconductor switching circuit means having a first input terminal, a second input terminal and an output terminal, a first signalling means for producing a first signal output, said output connected by a single conductor to the first input terminal of the semiconductor switching means, a second signalling means for producing a second signal output, said output connected to the second input of the semiconductor switching means, and a first responsive means connected to the output terminal of the switching means and a second responsive means connected to the single conductor of said first signalling means, the semiconductor switching circuit means producing a first output signal at its output terminal for operating the first responsive means, said first switching output signal being produced in response to the first output signal from the first signalling means, independent of the signal from said second signalling means, and the switching means also producing a second output signal at its first input terminal in response to the second output signal from the second signalling means, for operating the second responsive means.
Claim 2
Dependent Claim
181 words
A switching circuit comprising a semiconductor switching circuit means having a first input terminal, a second input terminal and an output terminal, a first signalling means for producing a first signal output, said output connected by a single conductor to the first input terminal of the semiconductor switching means, a second signalling means for producing a second signal output, said output connected to the second input of the semiconductor switching means, and a first responsive means connected to the output terminal of the switching means and a second responsive means connected to the single conductor of said first signalling means, the semiconductor switching circuit means producing a first output signal at its output terminal for operating the first responsive means, said first switching output signal being produced in response to the first output signal from the first signalling means, independent of the signal from said second signalling means, and the switching means also producing a second output signal at its first input terminal in response to the second output signal from the second signalling means, for operating the second responsive means.
Claim 3
Dependent Claim
181 words
A switching circuit comprising a semiconductor switching circuit means having a first input terminal, a second input terminal and an output terminal, a first signalling means for producing a first signal output, said output connected by a single conductor to the first input terminal of the semiconductor switching means, a second signalling means for producing a second signal output, said output connected to the second input of the semiconductor switching means, and a first responsive means connected to the output terminal of the switching means and a second responsive means connected to the single conductor of said first signalling means, the semiconductor switching circuit means producing a first output signal at its output terminal for operating the first responsive means, said first switching output signal being produced in response to the first output signal from the first signalling means, independent of the signal from said second signalling means, and the switching means also producing a second output signal at its first input terminal in response to the second output signal from the second signalling means, for operating the second responsive means.
Claim 4
Dependent Claim
181 words
A switching circuit comprising a semiconductor switching circuit means having a first input terminal, a second input terminal and an output terminal, a first signalling means for producing a first signal output, said output connected by a single conductor to the first input terminal of the semiconductor switching means, a second signalling means for producing a second signal output, said output connected to the second input of the semiconductor switching means, and a first responsive means connected to the output terminal of the switching means and a second responsive means connected to the single conductor of said first signalling means, the semiconductor switching circuit means producing a first output signal at its output terminal for operating the first responsive means, said first switching output signal being produced in response to the first output signal from the first signalling means, independent of the signal from said second signalling means, and the switching means also producing a second output signal at its first input terminal in response to the second output signal from the second signalling means, for operating the second responsive means.
Claim 5
Dependent Claim
17 words
A switching circuit as in claim 1 wherein the semiconductor switching circuit is a transistor switching circuit.
Claim 6
Dependent Claim
125 words
A switching circuit as in claim 1 wherein the switching circuit is used in an intercom signalling circuit of a key telephone system, the semiconductor switching means is connected to a key telephone, the first signalling means is a key service unit having an output signal for signalling the key telephone, the output of the key service unit is connected to the key telephone by a single conductor intercom line, the second signalling means is a hookswitch, the first responsive means is a call relay means used to signal an incoming call at a key telephone from the key service unit, and the second responsive means is a busy indication lamp in a busy indication lamp field indicating when the key telephone hookswitch is closed.
Claim 7
Dependent Claim
143 words
A switching circuit as in claim 3 wherein the semiconductor switching circuit is comprised of a diode and two transistors connected in opposition to each other, in which the first input terminal is connected through the forward biased diode to the emitters of the transistors, the second input terminal is connected directly to the emitters of the transistors, the call relay means is connected to the collector circuit of the second transistor, the second transistor has its base connected to the collector of the second transistor and the collector and base of the first transistor are connected through resistors to a power source for operating the call relay, whereby the signal from the key service unit operates the call relay independent of the position of the hookswitch and the hookswitch operates the busy indication lamp independent of the operation of the call relay.
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) | 1978-06-02 | 1978-12-02 | 1979-06-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-06-02 | 1982-12-02 | 1983-06-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-06-02 | 1986-12-02 | 1987-06-03 | $7700.00 | Window Closed / Lapsed |