US4484034A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Anti-larsen-effect arrangement in a telephone station equipped with a loudspeaker
Assignee: Telecommunications Radioelectriques et Telephoniques SA TRT
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Filing: 1983-06-07
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Granted: 1984-11-20
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Expires: 2003-06-07
Abstract
Abstract An anti-Larsen circuit for a telephone station in which the listening channel comprises an automatic listening level control circuit, suitably of the type comprising a variable attenuator circuit, a pulse-width modulator and a threshold detector which supplies compression pulses. The transmission channel comprises a circuit for rendering the transmission channel operative or inoperative and also a control circuit. Actuation takes place above a sound-level threshold S 1 and a de-activation below a sound-level threshold S 2 which is smaller than S 1 .
Inventors
- 👤 Gilbert M. M. Ferrieu
- 👤 Roger B. J. Hamel
- 👤 Emmanuel Lefort
- 👤 Francoise Moliere
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 16:35
CPC Classifications
H; H04; H04M; H04M9/00; H04M9/08
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
343 words
An anti-Larsen-effect arrangement in a telephone station having a transmission channel and a listening channel, said listening channel comprising first means for automatic listening signal level control, a speaker amplifier whose gain is manually variable and a loudspeaker, said first means comprising a variable attenuation circuit for attenuating said listening signal in response to compression signals, a pulse width modulator connected between said variable attenuator circuit and said speaker amplifier for pulse width modulating said listening signal which is then amplified by said speaker amplifier and delivered to said loudspeaker, and a threshold detector responsive to the signal supplied by the pulse width modulator which produces a compression signal pulse each time that it detects that the amplitude of the signal received by said microphone reaches a certain threshold, said transmission channel comprising a microphone for supplying an output signal in response to a sound signal received by said microphone, second means connected to said microphone for selectively attenuating the level of the output signal of said microphone to provided a transmit signal, an amplifier having a generally fixed gain connected to said second means for amplifying the transmit signal, and a control chain for said second means, which chain receives the output signal from said microphone and controls said second means to attenuate the level of the transmit signal when the level of the sound signal received by said microphone is less than a sound level threshold S 1 , the level of the sound signal received by said microphone from said loudspeaker and which is caused by a remote user being assumed to be lower than level threshold S 1 and the sound signal received by said microphone and produced by a local user being assumed to be within a range including level threshold S 1 , and while said chain is selectively not controlling said second means to attenuate said transmit signal said chain provides an additional compression signal S O to said first means to control said variable attenuator circuit to obtain a predetermined attenuation of the listening signal.
Claim 2
Dependent Claim
343 words
An anti-Larsen-effect arrangement in a telephone station having a transmission channel and a listening channel, said listening channel comprising first means for automatic listening signal level control, a speaker amplifier whose gain is manually variable and a loudspeaker, said first means comprising a variable attenuation circuit for attenuating said listening signal in response to compression signals, a pulse width modulator connected between said variable attenuator circuit and said speaker amplifier for pulse width modulating said listening signal which is then amplified by said speaker amplifier and delivered to said loudspeaker, and a threshold detector responsive to the signal supplied by the pulse width modulator which produces a compression signal pulse each time that it detects that the amplitude of the signal received by said microphone reaches a certain threshold, said transmission channel comprising a microphone for supplying an output signal in response to a sound signal received by said microphone, second means connected to said microphone for selectively attenuating the level of the output signal of said microphone to provided a transmit signal, an amplifier having a generally fixed gain connected to said second means for amplifying the transmit signal, and a control chain for said second means, which chain receives the output signal from said microphone and controls said second means to attenuate the level of the transmit signal when the level of the sound signal received by said microphone is less than a sound level threshold S 1 , the level of the sound signal received by said microphone from said loudspeaker and which is caused by a remote user being assumed to be lower than level threshold S 1 and the sound signal received by said microphone and produced by a local user being assumed to be within a range including level threshold S 1 , and while said chain is selectively not controlling said second means to attenuate said transmit signal said chain provides an additional compression signal S O to said first means to control said variable attenuator circuit to obtain a predetermined attenuation of the listening signal.
Claim 3
Dependent Claim
129 words
An anti-Larsen-effect arrangement as claimed in claim 1 wherein said control chain controls said second means to selectively not attenuate the level of the transmit signal when the sound level received by the microphone has exceeded said first sound level threshold S 1 and subsequently remains at a level higher than a second sound-level threshold S 2 , which is below or equal to S 1 , and to selectively attenuate the level of the transmit signal when the level of the sound signal received by said microphone has decreased below the level threshold S 2 for a predetermined time, the sound signal received by said microphone and produced by the local user being assumed to be situated within a sound-level range above the level threshold S 2 .
Claim 4
Dependent Claim
74 words
An anti-Larsen-effect arrangement as claimed in claim 2 wherein said control has a time constant for selectively not attenuating the transmit signal that is small relative to a time constant for controlling said first means to attenuate the listening signal and has a time constant for attenuating the transmit signal, which is of the order of 100 ms, and which is fast relative to a time constant for selectively not attenuating the listening signal.
Claim 5
Dependent Claim
61 words
An anti-Larsen-effect arrangement as claimed in claim 1 wherein said compression pulses from the threshold detector are applied to said variable attenuator circuit to control the charge of an intergrator circuit which supplies an attenuation control signal, said first means having time constants that are fast during actuation in order to follow the increase of a signal and slow during deactivation.
Claim 6
Dependent Claim
59 words
An anti-Larsen-effect arrangement as claimed in any one of the the claims 1 to 4 wherein said additional compression signal S O depends on the manually variable gain of the speaker amplifier so as to obtain a reduction of the effect of the signal S O on the attenuation of the listening signal when said manually variable gain decreases.
Claim 7
Dependent Claim
27 words
An anti-Larsen-effect arrangement as claimed in claim 5 wherein the effect produced by the signal S O is controlled to be proportional to said manually variable gain.
Claim 8
Dependent Claim
132 words
An anti-Larsen-effect arrangement as claimed in any one of the claims 1 to 4 wherein said control chain comprises, in cascade between the output of said microphone and a control input of said second means, a resistor, a tapping, a logic element, a NAND-gate circuit, an npn-transistor, whose collector is connected to a current source and whose emitter is connected to earth, a capacitor C 1 , included between said current source and earth, a diode, and the positive input of a differential amplifier which receives a constant voltage level on its negative input, said tapping receiving an auxiliary signal, after integration, which signal can be rendered active and inactive by the output of said differential amplifier, said auxiliary signal being also applied directly to a second input of said logic element.
Claim 9
Dependent Claim
23 words
An anti-Larsen-effect arrangement as claimed in claim 7 wherein compression signal S O is provided by the output signal of said differential amplifier.
Claim 10
Dependent Claim
65 words
An anti-Larsen-effect arrangement as claimed in any one of the claims 1 to 4 wherein said second means in the transmission channel comprises an npn-transistor which is controlled on its base, whose collector is connected to the input of said transmission amplifier via a resistor, and whose emitter is connected to a negative power supply terminal (earth) and may be provided with a collector resistor.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1987-11-20 | 1988-05-21 | 1988-11-20 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-11-20 | 1992-05-21 | 1992-11-20 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-11-20 | 1996-05-21 | 1996-11-20 | $7700.00 | Window Closed / Lapsed |