Transmit/receive network for telephone-subscriber station

Details Transmit/receive network for telephone-subscriber station Transmit/receive network for telephone-subscriber station

1977-12-01

1979-03-27

Claffy, Kathleen H.

179170T, H04M 158

Patent

active

041467531

ABSTRACT:
A receiving amplifier AR and a transmitting amplifier AT at a telephone-subscriber station have operating circuits in respective diagonals A-D and B-C of a bridge circuit whose four impedance arms are formed by two fixed resistances Z.sub.1, Z.sub.2, a variable resistance Z.sub.3 and the resistance Z.sub.4 of a line linking the subscriber station with an associated central office. The variable bridge resistance Z.sub.3 includes a plurality of resistors selectively insertable under the control of a voltage sensor and stabilizer SL connected across the transmitting diagonal B-C which also biases a variable-gain input stage of each amplifier AR, AT to adapt it to the line resistance. A final stage of the transmitting amplifier AT has an input connected via a negative-feedback resistance ZA to one of its output terminals whereby the effective resistance of this amplifier is reduced to a small fraction of the two bridge resistances Z.sub.1, Z.sub.3 in parallel therewith. A microphone M and an earpiece RC, respectively connected to the input of the transmitting amplifier AT and to the output of the receiving amplifier AR, may be constituted by identical electro-acoustic transducers. A tone generator DS, serving for the emission of call-number digits, can be energized from the sensor SL and has an output which blocks the input stage of the transmitting amplifier during such emission.

REFERENCES:
patent: 3546395 (1970-12-01), Schuh
patent: 3582564 (1971-06-01), Knauer
patent: 3708630 (1973-01-01), Matsuda et al.
patent: 3711660 (1973-01-01), Cherry
patent: 3742153 (1973-06-01), Matsuda et al.
patent: 3748400 (1973-07-01), Ritz et al.
patent: 3974344 (1976-08-01), Mersich
patent: 4031331 (1977-06-01), Sencer
patent: 4071713 (1978-01-01), Sencer

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