Method and apparatus for decreasing distortion in a line powered modulator circuit

• US 6,661,892 B1
• Filed: 03/30/1999
• Issued: 12/09/2003
• Est. Priority Date: 03/30/1999
• Status: Expired due to Fees

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems Incorporated (Broadcom, Inc.)
• Inventors: Fischer, Jonathan Herman
• Primary Examiner(s): Harvey, Minsun Oh
• Assistant Examiner(s): HAROLD, JEFFEREY F
• Application Number:
  US09/280,473
• Time in Patent Office: 1,715 Days
• Field of Search: 379/387.01, 379/391, 379/402, 379/404, 379/412, 379/93.01
• US Class Current: 379/391
• CPC Class Codes: H04M 19/001 Current supply source at the exchanger providing current to substations

Abstract

A method and apparatus for a telephone line interface or data access arrangement (DAA) which includes a shunt regulator in series with a line modulator. A first sense resistor is placed in series between the shunt regulator and the line modulator to provide a measurement of the amount of current distortion in the DAA shunt regulator. The voltage across the first sense resistor is fed back to the line modulator. A second sense resistor is inserted into the line modulator circuitry to provide a measurement of the system current distortion that is outside of the path containing the sense resistor used to monitor the current distortion in the DAA shunt regulator. The voltage across the second sense resistor is also fed back to the line modulator. The line modulator is capable of adjusting the AC modulation and the DC termination presented to the telephone line. The method includes drawing power from the telephone line using a shunt regulator, modulating the telephone line in series with the shunt regulator, sensing a level of distortion in the shunt regulator, sensing a level of distortion outside the shunt regulator, and feeding the sensed levels of distortion to the line modulator.

Claims

1. A telephone line interface circuit for placing an information signal on a telephone line comprising:

a line modulator for receiving an information signal, said line modulator coupled to said telephone line for modulating said telephone line with said information signal;

a first sense resistor coupled to said line modulator so as to sense a current through said line modulator;

a second sense resistor electrically connected within said line modulator for sensing an error current introduced by said line modulator,

a first feedback path from said first sense resistor to said line modulator; and

a second feedback path containing said second sense resistor;

such that said line modulator incorporates said current through said first sense resistor, said current through said second sense resistor, and said information signal.

2. A telephone line interface circuit as set forth in claim 1 further comprising a shunt regulator coupled in series with said first sense resistor on said telephone line.

3. A telephone line interface circuit as set forth in claim 2 wherein said line modulator comprises a first transistor.

4. A telephone line interface circuit as set forth in claim 3 wherein said line modulator further comprises an amplifier having an output coupled to a control terminal of said first transistor so as to control the current flowing through current flow terminals of said first transistor, said amplifier being coupled to receive at inputs thereto said current through said first sense resistor, said current through said second sense resistor and said information signal.

5. A telephone line interface circuit as set forth in claim 4 wherein said line modulator comprises a second transistor coupled between said output terminal of said amplifier and said control terminal of said first transistor such that said current flowing through said current flow terminals of said first transistor is controlled as a function of said current through said first sense resistor, said current through said second sense resistor and said information signal.

6. A telephone line interface circuit as set forth in claim 4 wherein a first of said current flow terminals of said first transistor is coupled with said first sense resistor and a second of said current flow terminals is coupled with said telephone line.

7. A telephone line interface circuit as set forth in claim 6 wherein said line modulator further comprises a second transistor having a collector coupled to said control terminal of said first transistor, an emitter coupled to said output terminal of said amplifier through said second sense resistor and a base terminal coupled between said first transistor and said first sense resistor.

8. A telephone line interface circuit as set forth in claim 6 wherein said line modulator further comprises a second transistor having a control terminal coupled to said output terminal of said amplifier, a collector coupled to said control terminal of said first transistor and an emitter coupled to said second sense resistor.

9. A telephone line interface circuit for placing an information signal on a telephone line comprising:

a shunt regulator;

a first sense resistor in series with said shunt regulator for sensing a current through said shunt regulator;

a line modulator electrically connected to said first sense resistor and said shunt regulator;

a second sense resistor electrically connected within said line modulator for sensing a current from the telephone line within said line modulator;

a first feedback path from said first sense resistor to said line modulator; and

a second feedback path to said modulator through said second sense resistor located within said modulator.

10. The telephone line interface according to claim 9, wherein:

said line modulator comprises a bipolar transistor.

11. The telephone line interface according to claim 10, wherein:

said bipolar transistor comprises a pnp bipolar transistor.

12. The telephone line interface according to claim 9, wherein:

said telephone line interface is a data access arrangement for a modem.

13. A telephone line interface circuit for placing an information signal on a telephone line comprising:

a first sense resistor for sensing a current on said telephone line;

a first transistor in series with said first sense resistor;

a second sense resistor coupled to sense the current on said telephone line outside of the current path of said first sense resistor;

a second transistor coupled between said second sense resistor and the base of said first transistor;

an amplifier having an input for accepting an information signal and an output electrically connected to said second transistor for modulating said telephone line with said information signal;

a first feedback path from said first sense resistor to said amplifier; and

a second feedback path from said second sense resistor to said amplifier.

14. The telephone line interface circuit according to claim 13, wherein;

said first and second transistors are bipolar transistors.

15. The telephone line interface circuit according to claim 14, wherein;

said first transistor is a pnp bipolar transistor; and

said second transistor is a npn bipolar transistor.

16. The telephone line interface circuit according to claim 15, wherein;

said amplifier controls the emitter of said second transistor; and

said second transistor controls the base of said first transistor through the collector of said second transistor;

such that said amplifier controls said first transistor.

17. The telephone line interface circuit according to claim 16, wherein;

said second sense resistor is connected between said output of said amplifier and the emitter of said second transistor; and

the base of said second transistor is connected to the collector of said first transistor.

18. The telephone line interface circuit according to claim 15, wherein;

said amplifier controls the base of said second transistor; and

said second transistor controls the base of said first transistor through the collector of said second transistor;

such that said amplifier controls said first transistor.

19. A method for placing an information signal on a telephone line, said method comprising:

modulating said telephone line with a modulator;

sensing a first current passing through said modulator;

sensing a second current within said modulator; and

feeding back said first and second currents to said modulator.

20. A telephone line interface circuit for placing an information signal on a telephone line, comprising:

means for drawing power from a telephone line;

means for modulating said telephone line with an information signal, said means for modulating being in series with said means for drawing power;

first means for sensing an amount of distortion in said telephone line interface circuit, said first means for sensing being connected in series with said means for drawing power and said means for modulating;

second means for sensing an amount of distortion in said telephone line interface circuit, said second means for sensing being connected within said means for modulating; and

means for feeding back said first sensed amount of distortion and said second sensed amount of distortion to said telephone line interface circuit.

21. A telephone line interface circuit for placing an information signal on a telephone line comprising:

a line modulator for receiving an information signal, said line modulator coupled to said telephone line for modulating said telephone line with said information signal;

a first sense resistor coupled to said line modulator so as to sense a current through said line modulator; and

a second sense resistor electrically connected within said line modulator for sensing an error current introduced by said line modulator;

such that said line modulator incorporates said current through said first sense resistor, said current through said second sense resistor, and said information signal.