US3789155A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Side-tone reducing circuit for a telephone subscribers instrument
Assignee: Post Office
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Filing: 1971-07-16
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Granted: 1974-01-29
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Expires: 1991-07-16
Abstract
Abstract A circuit for a telephone subscriber''s instrument is described including a transistor amplifier in grounded emitter connection for amplifying signals from the transmitter and applying them to the exchange line. A tapped negative feedback path over the amplifier is provided and a receiver is connected to the tapping so that little sidetone from the transmitter is heard, but signals from the exchange line are not greatly attenuated. A zener diode in the emitter circuit of the transistor can be used to produce supply voltage for transmitter and receiver amplifiers. The transmitter amplifier may be provided with a positive feedback path which is effective when the handset is replaced on the cradle so that the transmitter generates an audible signal in response to a calling tone from the exchange.
Inventors
- 👤 H Fensom
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 23:01
CPC Classifications
H; H04; H04M; H04M19/00; H04M19/02; H04M19/04; H04M1/00; H04M1/58; H04M1/585; H04M9/00; H04M9/08
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
211 words
A circuit arrangement for a telephone subscriber''s instrument for connection to the conductors of a telephone exchange line, comprising a transmitting means having a single transistor amplifier for connection to the line and providing a desired output impedance characteristic and a 180* phase shift, the exchange line being connected so as to form the output load of the amplifier, a receiving means, and a tapped impedance circuit connected from the output to the input of the amplifier, in which the impedance of the tapped impedance circuit is chosen so that the arrangement presents to the conductors of the exchange line substantially the same impedance as the conductors of the exchange line present to the arrangement, said receiving means being connected from the tapping of the tapped impedance circuit to the emitter circuit of the transistor so that sidetone from the transmitting means in the receiving means is reduced, wherein the transistor of the amplifier is connected in grounded emitter configuration, with the conductors of the exchange line respectively connected to the emitter and collector circuits of the transistor amplifier, the transmitting means is connected to apply a signal between base and emitter of the transistor, and the tapped impedance circuit is connected from the collector of the transistor to its base.
Claim 2
Dependent Claim
211 words
A circuit arrangement for a telephone subscriber''s instrument for connection to the conductors of a telephone exchange line, comprising a transmitting means having a single transistor amplifier for connection to the line and providing a desired output impedance characteristic and a 180* phase shift, the exchange line being connected so as to form the output load of the amplifier, a receiving means, and a tapped impedance circuit connected from the output to the input of the amplifier, in which the impedance of the tapped impedance circuit is chosen so that the arrangement presents to the conductors of the exchange line substantially the same impedance as the conductors of the exchange line present to the arrangement, said receiving means being connected from the tapping of the tapped impedance circuit to the emitter circuit of the transistor so that sidetone from the transmitting means in the receiving means is reduced, wherein the transistor of the amplifier is connected in grounded emitter configuration, with the conductors of the exchange line respectively connected to the emitter and collector circuits of the transistor amplifier, the transmitting means is connected to apply a signal between base and emitter of the transistor, and the tapped impedance circuit is connected from the collector of the transistor to its base.
Claim 3
Dependent Claim
37 words
An arrangement according to claim 1, in which there is provided a second amplifier for amplifying an output signal from the transmitting means and applying the amplified signal across the base and emitter electrodes of the transistor.
Claim 4
Dependent Claim
59 words
An arrangement according to claim 1, in which there is provided a third amplifier, having an input connected from the tapping of the impedance circuit to the emitter circuit of the transistor and an output connected to the receiving means so as to amplify the signal appearing at the tapping, and applying the amplified signal to the receiving means.
Claim 5
Dependent Claim
37 words
An arrangement according to claim 2, in which a zener diode is provided in the emitter circuit of the transistor and a substantially constant supply voltage for the second amplifier is derived from across the zener diode.
Claim 6
Dependent Claim
36 words
An arrangement according to claim 3, in which a zener diode is provided in the emitter circuit of the transistor and a substantially constant supply voltage for the amplifier is derived from across the zener diode.
Claim 7
Dependent Claim
270 words
A circuit arrangement for a telephone subscriber''s instrument for connection to the contacts of a telephone exchange line, comprising a transmitting means having a single transistor amplifier for connection to the line and providing a desired output impedance characteristic and a 180* phase shift, the exchange line being connected so as to form the output load of the amplifier, a receiving means and a tapped impedance circuit connected from the output to the input of the amplifier, in which the impedance of the tapped impedance circuit is chosen so that the arrangement presents to the conductors of the exchange line substantially the same impedance as the conductors of the exchange line present to the arrangement, said receiving means being connected from the tapping of the tapped impedance circuit to the emitter circuit of the transistor so that sidetone from the transmitting means in the receiving means is reduced, wherein the transistor of the amplifier is connected in grounded emitter configuration, with the conductors of the exchange line respectively connected to the emitter and collector circuits of the transistor amplifier, a second amplifier is provided for amplifying an output signal from the transmitting means and applying the amplified signal across the base and emitter electrodes of the transistor, the tapped impedance circuit is connected from the collector of the transistor to its base, and switchable feedback means is provided in the second amplifier to enable that amplifier to oscillate at an audible frequency, so that in response to a calling tone signal from the exchange an audiBle calling signal is generated by the transmitting means when the feedback means is effective.
Claim 8
Dependent Claim
270 words
A circuit arrangement for a telephone subscriber''s instrument for connection to the contacts of a telephone exchange line, comprising a transmitting means having a single transistor amplifier for connection to the line and providing a desired output impedance characteristic and a 180* phase shift, the exchange line being connected so as to form the output load of the amplifier, a receiving means and a tapped impedance circuit connected from the output to the input of the amplifier, in which the impedance of the tapped impedance circuit is chosen so that the arrangement presents to the conductors of the exchange line substantially the same impedance as the conductors of the exchange line present to the arrangement, said receiving means being connected from the tapping of the tapped impedance circuit to the emitter circuit of the transistor so that sidetone from the transmitting means in the receiving means is reduced, wherein the transistor of the amplifier is connected in grounded emitter configuration, with the conductors of the exchange line respectively connected to the emitter and collector circuits of the transistor amplifier, a second amplifier is provided for amplifying an output signal from the transmitting means and applying the amplified signal across the base and emitter electrodes of the transistor, the tapped impedance circuit is connected from the collector of the transistor to its base, and switchable feedback means is provided in the second amplifier to enable that amplifier to oscillate at an audible frequency, so that in response to a calling tone signal from the exchange an audiBle calling signal is generated by the transmitting means when the feedback means is effective.
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) | 1977-01-28 | 1977-07-30 | 1978-01-29 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-01-28 | 1981-07-30 | 1982-01-29 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-01-28 | 1985-07-30 | 1986-01-29 | $7700.00 | Window Closed / Lapsed |