Line-powered modem with capacitive isolation

• US 5,655,010 A
• Filed: 08/11/1995
• Issued: 08/05/1997
• Est. Priority Date: 08/11/1995
• Status: Expired due to Term

• Current Assignee: Xylon LLC (Intellectual Ventures LLC)
• Original Assignee: Paradyne Corporation (Dasan Networks Incorporated)
• Inventors: Bingel, Thomas J.
• Primary Examiner(s): Chan, Wing F.
• Application Number:
  US08/514,040
• Time in Patent Office: 725 Days
• Field of Search: 379/96-98, 379/93, 379/94, 379/395, 379/405, 379/379, 379/376, 379/412, 379/406, 379/413, 379/345, 379/377, 379/399, 379/387, 379/398, 379/375, 375/222
• US Class Current: 379/93.28
• CPC Class Codes: H04L 12/10 Current supply arrangements
• CPC Class Codes: H04M 11/06 Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors
• CPC Class Codes: H04M 19/08 with current supply sources at the substations generating ringing current H04M19/04

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.

Claims

1. A modem comprising a first modem circuit including a transmitter for providing an outgoing digital data signal, a receiver for receiving an incoming digital data signal, and a control means for providing a pair of control signals;

a coder/decoder (CODEC) means coupled to a telephone line for providing said incoming digital data signal by encoding an incoming analog telephone signal received via said telephone line and for providing an outgoing analog telephone signal for transmission over said telephone line by decoding said outgoing digital data signal;

a first power source, which does not draw power from said telephone line, for supplying a potential, with respect to a first reference ground, to said first modem circuit;

a second power source functionally connected to said telephone line for supplying a potential, with respect to a second reference ground, to said CODEC means by drawing power only from said telephone line; and

isolation means connected between said CODEC means and said first modem circuit for electrically isolating said CODEC means from said first modem circuit;

characterized in that said isolation means includes a first capacitive isolator means having a coupling capacitor with two terminals for coupling said incoming digital data signal from said CODEC means to said first modem circuit, a second capacitive isolator means having a coupling capacitor with two terminals for coupling said outgoing digital data signal from said first modem circuit to said CODEC means, third and fourth capacitive isolator means each having coupling capacitors with two terminals for coupling said pair of control signals from said control means to said CODEC means, a capacitor connected between said first reference ground and said second reference ground, and a latch circuit having an input connected to one of the terminals of the coupling capacitor of at least of the capacitor isolator means.

2. The modem as defined in claim 1, wherein the input of a latch circuit is connected to the coupling capacitor of the first capacitive isolator means.

3. The modem as defined m claim 1, wherein the input of a latch circuit is connected to the coupling capacitor of the second capacitive isolator means.

4. The modem as defined in claim 1, wherein the input of a latch circuit is connected to the coupling capacitor of the both the third and fourth capacitive isolator means.

5. A modem as defined in claims 2, 3, or 4 wherein said latch circuit comprises an inverter circuit having an input and an output, a nand gate having two inputs and an output, means for connecting the output of said inverter circuit to one of said two inputs of said nand gate, a feedback resistor connected between the output of said nand gate and the input of said inverter circuit, and a reset means connected to the other of said two inputs of said nand gate for momentarily connecting a potential equivalent to a logic zero to said other input of said nand gate when said at least one latch circuit is first energized with power.

6. A data access arrangement circuit for electrically isolating a telephone line from a first modem circuit including a transmitter for providing an outgoing digital data signal, a receiver for receiving an incoming digital data signal, and a control means for providing a pair of control signals;

said first modem circuit powered only by a first power source that provides a potential with respect to a first reference ground and which does not draw power from said telephone line;

said data access arrangement circuit comprising a CODEC means coupled to said telephone line for providing said incoming digital data signal by encoding an incoming analog telephone signal received from said telephone line and for providing an outgoing analog telephone signal for transmission over said telephone line by decoding said outgoing digital data signal;

a second power source for supplying a potential with respect to a second reference ground to said CODEC means by drawing power only from said telephone line; and

isolation means connected between said CODEC means and said first modem circuit for electrically isolating said CODEC means from said first modem circuit;

characterized in that said isolation means includes a first capacitive isolator means having a coupling capacitor with two terminals for coupling said incoming digital data signal from said CODEC means to said first modem circuit, a second capacitive isolator means having a coupling capacitor with two terminals for coupling said outgoing digital data signal from said first modem circuit to said CODEC means, third and fourth capacitive isolator means each having coupling capacitors with two terminals for coupling said pair of control signals from said control means to said CODEC means, a capacitor connected between said first reference ground and said second reference ground, and a latch circuit having an input connected to one of the terminals of the coupling capacitor of at least of the capacitor isolator means.

7. The data access arrangement circuit as defined in claim 6, wherein the input of a latch circuit is connected to the coupling capacitor of the first capacitive isolator means.

8. The data access arrangement circuit as defined in claim 6, wherein the input of a latch circuit is connected to the coupling capacitor of the second capacitive isolator means.

9. The data access arrangement circuit as defined in claim 6, wherein the input of a latch circuit is connected to the coupling capacitor of the both the third and fourth capacitive isolator means.

10. A data access arrangement circuit as defined in claims 7, 8, or 9 wherein said latch circuit comprises an inverter circuit having an input and an output, a nand gate having two inputs and an output, means for connecting the output of said inverter circuit to one of said two inputs of said nand gate, a feedback resistor connected between the output of said nand gate and the input of said inverter circuit, and a reset means connected to the other of said two inputs of said nand gate for momentarily connecting a potential equivalent to a logic zero to said other input of said nand gate when said at least one latch circuit is first energized with power.

11. A capacitive isolator circuit for a modem comprising:

a coupling capacitor having a first terminal and a second terminal;

a driver circuit having an output electrically connected to the first terminal;

a latch circuit having an input electrically connected to the second terminal, the latch circuit further including an inverter circuit having an input and an output, a nand gate having a first and second input and an output, means for connecting the output of the inverter circuit to the first input of the nand gate, a feedback resistor connected between the output of the nand gate and the input of the inverter circuit, and a reset means connected to the second input of said nand gate for momentarily connecting a potential equivalent to a logic zero to the second input of the nand gate when the latch circuit is first energized with power.