Line-powered modem with capacitive isolation

Details Line-powered modem with capacitive isolation Line-powered modem with capacitive isolation

1995-08-11

1997-08-05

Chan, Wing F.

Telephonic communications

Telephone line or system combined with diverse electrical...

Having transmission of a digital message signal over a...

379412, 375222, H04M 1100

Patent

active

056550103

ABSTRACT:
A modem is disclosed which is separated into two parts, a first modem circuit consisting of digital circuits, and a second modem circuit consisting of a CODEC and analog circuits. The two modem circuits are separately powered by a first and second power source, respectively, and connected by an isolation circuit. The second power source derives all of its power from the telephone line to which the modem is connected. The portions of the isolation circuit which transfer data and control signals between the first and second modem circuits are constructed using coupling capacitors and latch circuits, and a similar capacitor is connected between the reference grounds of the first and second power sources. Each latch circuit uses a nand gate having two inputs, one of which is connected to momentarily receive a potential equivalent to logical zero, thereby providing a reset when the modem is first energized.

REFERENCES:
patent: 5086454 (1992-02-01), Hirzel
patent: 5369687 (1994-11-01), Farkas
patent: 5500895 (1996-03-01), Yurgelites

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