Central office interface techniques for digital subscriber lines

• US 6,850,618 B1
• Filed: 05/15/2000
• Issued: 02/01/2005
• Est. Priority Date: 05/15/2000
• Status: Expired due to Term

• Current Assignee: Ikanos Communications Incorporated (Qualcomm, Inc.)
• Original Assignee: Centillium Communications Incorporated (Transwitch Corporation)
• Inventors: Babaei, Heron, Kiykioglu, Serdar, Mohajeri, Hessam
• Primary Examiner(s): Harvey, Minsun Oh
• Assistant Examiner(s): Tran, Con P.
• Application Number:
  US09/570,804
• Time in Patent Office: 1,723 Days
• Field of Search: 379/399.01, 379/399.02, 379/142.01, 379/93.08, 379/373.01, 379/414, 370/493, 370/252, 370/295, 375/222
• US Class Current: 379/399.01
• CPC Class Codes: H04M 11/062 using different frequency bands for speech and other data

Abstract

A splitterless interface between a digital subscriber line (DSL) and the central office equipment that can receive and isolate the low frequency voice data and high frequency digital data from a telephone line. This interface can also mix and transmit low frequency voice data and high frequency digital data onto a telephone line. For POTS band frequencies, a reactive impedance coupled across the two-wire interface of the POTS line card, and serially coupled to the line side of the DSL coupling transformer, has an open state magnitude. The magnitude of the line side windings of the DSL coupling transformer is low at POTS band frequencies. POTS band signal power is therefore delivered to the POTS line card. For DSL band frequencies, the reactive impedance across the two-wire interface of the POTS line card has a closed state magnitude. The POTS line card is therefore essentially short-circuited at DSL band frequencies, and DSL band signal power is delivered to the DSL modem. The frequency band in which the reactive impedance transitions from an open state magnitude to a closed state magnitude corresponds to the frequency band between the POTS frequency band and the DSL frequency band.

Claims

1. A system for interfacing a telephone line having a first wire and a second wire with a central office, the system comprising:

a DSL modem connected to a coupling transformer having a line side and a circuit side, the modem for processing DSL frequency band signals received from the telephone line, wherein the line side of the transformer is coupled between the first and second wires of the telephone line;

a reactive impedance serially coupled to the line side of the transformer, the reactive impedance having a magnitude that decreases as signal frequency increases;

a POTS line card having a two-wire interface, and for processing POTS frequency band signals received from the telephone line, wherein the two-wire interface of the POTS line card is operatively coupled across the reactive impedance.

2. The system of claim 1 wherein the reactive impedance has an open state magnitude in response to POTS frequency band signals.

3. The system of claim 1 wherein the reactive impedance has a closed state magnitude in response to DSL frequency band signals.

4. The system of claim 1 wherein the POTS line card includes a CODEC that is programmed to compensate for effects the reactive impedance has on POTS band structural impedance.

5. The system of claim 1 further comprising:

a ringing circuit coupled to the POTS line card for ringing a telephone set on the telephone line wherein, responsive to a ringing signal from the ringing circuit, the reactive impedance has an open state magnitude.

6. The system of claim 1 further comprising:

a ringing circuit coupled to the POTS line card for ringing a telephone set on the telephone line wherein, responsive to receiving DSL frequency band signals, the reactive impedance has a closed state magnitude thereby inhibiting the DSL frequency band signals from being delivered to the ringing circuit.

7. The system of claim 1 wherein at least a portion of the system is implemented by one or more integrated circuit chips.

12. The method of claim 1 further comprising:

compensating for effects of the DC blocking capacitor operatively coupled across the two-wire interface of the POTS circuit with a CODEC included in the POTS circuit.

8. A method for interfacing a telephone line having a first wire and a second wire with a central office, the method operating in a system comprising a reactive impedance that is operatively coupled to a two-wire interface of a POTS line card, wherein the reactive impedance is serially coupled to a line side of a coupling transformer, and the line side of the coupling transformer is connected between the first and second wires of the telephone line, the method comprising:

receiving at the POTS line card a first signal having a first frequency that causes the reactive impedance to have an open state magnitude thereby inhibiting the first signal from being transferred from the line side of the transformer to a circuit side of the transformer; and

receiving at a DSL modem that is connected to the circuit side of the coupling transformer a second signal having a second frequency that causes the reactive impedance to have a closed state magnitude thereby inhibiting the second signal from being delivered to the POTS line card.

9. A method for interfacing a telephone line having a first wire and a second wire with a central office, the method operating in a system comprising a reactive impedance that is operatively coupled to a two-wire interface of a POTS circuit, wherein the reactive impedance is serially coupled to a line side of a coupling transformer, the line side of the transformer being connected between the first and second wires of the telephone line, the method comprising:

responsive to a first signal having a POTS band frequency, providing an open state magnitude of the reactive impedance thereby allowing power of the first signal to be delivered to the POTS circuit; and

responsive to a second signal having a DSL band frequency, providing a closed state magnitude of the reactive impedance thereby inhibiting the second signal from being delivered to the POTS circuit.

10. The method of claim 9 wherein providing a closed state magnitude of the reactive impedance in response to the second signal inhibits the second signal from being delivered to a ringing circuit coupled to the POTS circuit, and allows power of the second signal to be delivered to a DSL modem circuit.

11. A method for interfacing a telephone line having first and second wires with a POTS circuit having a two-wire interface, wherein a DC blocking capacitor of a coupling transformer is operatively coupled across the two-wire interface of the POTS circuit, the method comprising:

responsive to a first signal having a POTS band frequency, providing an open state magnitude of the DC blocking capacitor thereby allowing power of the first signal to be delivered to the POTS circuit; and

responsive to a second signal having a DSL band frequency, providing a closed state magnitude of the DC blocking capacitor thereby inhibiting power of the second signal from being delivered to the POTS circuit.

13. The method of claim 11 wherein providing a closed state magnitude of the DC blocking capacitor in response to the second signal inhibits power of the second signal from being delivered to a ringing circuit coupled to the POTS circuit.

14. A system for interfacing a telephone line having a first wire and a second wire with a central office, the system comprising:

a first signal processor for receiving a high frequency analog signal from the telephone line, the first signal processor including a transformer having a line side that is coupled between the first and second wires of the telephone line;

a reactive impedance serially coupled to the line side of the transformer, the reactive impedance for providing an impedance having a magnitude that decreases as signal frequency increases; and

a second signal processor for receiving a POTS band analog signal from the telephone line, the second signal processor having a two-wire interface, and the reactive impedance is coupled across the two-wire interface.

15. The system of claim 14 wherein the reactive impedance has an open state magnitude in response to receiving the POTS band analog signal thereby allowing power of the POTS band analog signal to be delivered to the second signal processor.

16. The system of claim 14 wherein the reactive impedance has a closed state magnitude in response to the high frequency analog signal thereby allowing power of the high frequency analog signal to be delivered to the first signal processor.

17. The system of claim 14 wherein the second signal processor includes a CODEC that is programmed to compensate for the reactive impedance coupled across the two-wire interface of the second signal processor.

18. A system for interfacing a telephone line having a first wire and a second wire with a central office, the system comprising:

a transformer having its line side coupled between the first and second wires of the telephone line, the transformer for decoupling DSL circuitry from the telephone line;

a capacitor serially coupled between first and second line side windings of the transformer; and

a POTS circuit having the capacitor coupled across its two-Wire interface, the POTS circuit for processing POTS frequency band signals received from the telephone line.

19. The system of claim 18 wherein the capacitor has an open state magnitude in response to POTS frequency band signals.

20. The system of claim 18 wherein the capacitor has a closed state magnitude in response to DSL frequency band signals.

21. The system of claim 18 wherein the POTS circuit includes a CODEC that is programmed to compensate for effects of the capacitor coupled across the two-wire interface of the POTS circuit.

22. The system of claim 18 wherein the POTS circuit includes a SLIC.

23. A method for interfacing a telephone line having a first wire and a second wire with a central office, the method operating in a system comprising a capacitor that is coupled across the two-wire interface of a POTS circuit, wherein the capacitor is serially coupled between first and second line side windings of a DSL coupling transformer, the method comprising:

responsive to a first signal having a POTS band frequency, providing an open state magnitude of the capacitor thereby allowing power of the first signal to be delivered to the POTS circuit; and

responsive to a second signal having a DSL band frequency, providing a closed state magnitude of the capacitor thereby inhibiting power of the second signal from being delivered to the POTS circuit.

24. A method for filtering POTS and DSL data received from a telephone line using a DSL coupling transformer and its DC blocking capacitor, the method comprising:

isolating the POTS data by virtue of the POTS data causing the DC blocking capacitor to have an open state magnitude thereby inhibiting the POTS data from being delivered to DSL circuitry; and

isolating the DSL data by virtue of the DSL data causing the DC blocking capacitor to have a closed state magnitude thereby inhibiting the DSL data from being delivered to POTS circuitry.