Telephonic communications – Subscriber line or transmission line interface
Patent
1994-09-12
1995-06-06
Dwyer, James L.
Telephonic communications
Subscriber line or transmission line interface
379402, 379345, H04B 332
Patent
active
054229480
ABSTRACT:
A subscriber line interface circuit, coupled between a telephone unit terminal and a switching system, includes a coding and decoding circuit for controlling analog voltages inputted thereinto and outputted therefrom, using a direct current bias voltage, and an interface circuit. The interface circuit has an amplifier for detecting the analog voltage output, a unit for detecting a direct current bias voltage of the analog voltage output, a subtracting unit for determining the difference between the detected analog voltage output and the detected bias voltage, and resistors for driving the telephone unit terminal on the two-wire side. The analog voltage and the direct current bias voltage output terminals of the encoding and decoding circuit are directly connected with the input terminal of the amplifier for detecting the outputted analog voltage and the interface circuit, respectively, so that only a desired alternating current signal is outputted to the telephone unit terminal on its two-wire side.
REFERENCES:
patent: 4682356 (1987-07-01), Minch et al.
patent: 4896351 (1990-01-01), Stader et al.
patent: 4916734 (1990-04-01), Stader et al.
patent: 4953206 (1990-08-01), Friesen et al.
Dwyer James L.
NEC Corporation
Shehata M.
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