Reduced-complexity common-mode noise cancellation system for DSL

• US 8,472,533 B2
• Filed: 05/02/2011
• Issued: 06/25/2013
• Est. Priority Date: 10/10/2008
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Wiese, Brian
• Primary Examiner(s): PHU, PHUONG M
• Application Number:
  US13/098,891
• Publication Number:
  US 20110206104A1
• Time in Patent Office: 785 Days
• Field of Search: 375/258, 375/257, 375/284, 375/285, 375/346, 375229-232, 375/222, 375/219, 375/220, 375/260, 370/201, 279/417
• US Class Current: 375/258
• CPC Class Codes: H04B 1/10 Means associated with receiver for limiting or suppressing noise or interference
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 25/0226 sounding signals per se
• CPC Class Codes: H04L 5/00 Arrangements affording multiple use of the transmission path

Abstract

A noise cancellation system has a first transformer with an input side and an output side, the input side having first and second taps coupled to a signal provider, and a center tap providing a first common-mode voltage signal. A first digital subscriber line (xDSL) modem has an input coupled to the output side of the first transformer and an output coupled to customer premises equipment (CPE) for providing an xDSL signal to the CPE. A second transformer has an input side and an output side, the input side having first and second taps coupled to a signal provider, and a center tap providing a second common-mode voltage signal. A second xDSL modem is coupled to the output side of the second transformer. The difference between the first and second common-mode voltage signals is provided to at least one of the first and second xDSL modems to filter out noise from the xDSL signal provided by that modem.

Claims

1. A noise cancellation system, comprising:

a first transformer having an input side and an output side, the input side having first and second taps coupled to a communication service provider and further having a center tap;

a first digital subscriber line (xDSL) modem having an input coupled to the output side of the first transformer and an output coupled to customer premises equipment (CPE) for providing an xDSL signal to the CPE;

a second transformer having an input side and an output side, the input side having first and second taps coupled to the communication service provider and further having a center tap;

a second xDSL modem coupled to the output side of the second transformer; and

a third transformer having an input side and an output side, the input side of the third transformer having one tap coupled to the center tap of the first transformer, and a second tap coupled to the center tap of the second transformer,

the output side of the third transformer being coupled to the first and second xDSL modems to reduce noise in the xDSL signal provided to the CPE.

2. The noise cancellation system of claim 1, wherein the first xDSL modem includes a digital signal processor (DSP) with a noise canceller.

3. The noise cancellation system of claim 2, wherein the second xDSL modem includes a second DSP with a noise canceller.

4. The noise cancellation system of claim 3, further comprising:

a third DSP having an input coupled to the output side of the third transformer and an output coupled to the first and second xDSL modems.

5. The noise cancellation system of claim 4, further comprising:

an analog filter and gain (AFG) circuit having an input side coupled to the output side of the third transformer and an output side; and

an analog/digital converter (ADC) having an input side coupled to the output side of the AFG circuit and an output side coupled to the input of the third DSP, the output of the third DSP being coupled to respective inputs of the first and second xDSL modems.

6. The noise cancellation system of claim 2, further comprising:

an analog filter and gain (AFG) circuit having an input side coupled to the output side of the first transformer and an output side; and

an analog/digital converter (ADC) having an input side coupled to the output side of the AFG circuit and an output side coupled to an input of the DSP.

7. The noise cancellation system of claim 6, further comprising:

a second DSP having an input coupled to the output side of the third transformer and an output coupled to the first and second xDSL modems.

8. The noise cancellation system of claim 7, further comprising:

a second AFG circuit having an input side coupled to the output side of the third transformer and an output side; and

a second ADC having an input side coupled to the output side of the second AFG circuit and an output side coupled to the input of the second DSP, the output of the second DSP being coupled to respective inputs of the first and second xDSL modems.

9. The noise cancellation system of claim 1, wherein the third transformer is configured to detect a difference between a first common mode voltage of a first xDSL line coupled to the first transformer and a second common mode voltage of a second xDSL line coupled to the second transformer.

10. The noise cancellation system of claim 9, wherein the difference between the first and second common mode voltages characterizes the noise on the first xDSL line and the second xDSL line.

12. The noise cancellation system of claim 9, wherein the first xDSL modem includes a digital signal processor (DSP) with a noise canceller.

13. The noise cancellation system of claim 12, further comprising:

an analog filter and gain (AFG) circuit having an input side coupled to the output side of the first transformer and an output side; and

an analog/digital converter (ADC) having an input side coupled to the output side of the AFG circuit and an output side coupled to an input of the DSP.

14. The noise cancellation system of claim 13, further comprising:

a second AFG circuit having an input side coupled to the output side of the second transformer and an output side; and

a second ADC having an input side coupled to the output side of the second AFG circuit and an output side coupled to an input of the DSP.

11. A noise cancellation system, comprising:

a first transformer having an input side and an output side, the input side having first and second taps coupled to a communication service provider and further having a center tap;

an xDSL modem having an input side coupled to the output side of the first transformer and an output side coupled to customer premises equipment (CPE) for providing an xDSL signal to the CPE; and

a second transformer having an input side with first and second taps, the first tap being coupled to the center tap of the first transformer and the second tap being coupled to a terminated wire pair;

the second transformer having an output side coupled to the xDSL modem to reduce noise in the xDSL signal provided to the CPE.

15. The noise cancellation system of claim 11, wherein the second tap of the second transformer is coupled to a common terminal of the terminated wire pair to provide a common mode of the terminated wire pair.

16. A noise cancellation system, comprising:

a first transformer having an input side and an output side, the input side having first and second taps coupled to a signal provider and further having a center tap and providing a first common-mode voltage signal;

a first digital subscriber line (xDSL) modem having an input coupled to the output side of the first transformer and an output coupled to customer premises equipment (CPE) for providing an xDSL signal;

a second transformer having an input side and an output side, the input side having first and second taps coupled to the signal provider and further having a center tap and providing a second common-mode voltage signal;

a second xDSL modem coupled to the output side of the second transformer;

means for taking the difference between the first and second common-mode voltage signals;

means for providing the difference to at least one of the first and second xDSL modems to filter out noise from the xDSL signal provided by that at least one modem; and

a third transformer having an input side and an output side, the input side of the third transformer having one tap coupled to the center tap of the first transformer, and a second tap coupled to the center tap of the second transformer,

the output side of the third transformer being coupled to the at least one xDSL modem to reduce noise in the xDSL signal provided to the CPE through the at least one xDSL modem.

17. The noise cancellation system of claim 16, wherein the at least one xDSL modem includes a digital signal processor (DSP) with a noise canceller.

18. The noise cancellation system of claim 16, further comprising:

a digital signal processor (DSP) having an input coupled to the output side of the third transformer and an output coupled to the at least one xDSL modem.

19. The noise cancellation system of claim 18, further comprising:

an analog filter and gain (AFG) circuit having an input side coupled to the output side of the third transformer and an output side; and

an analog/digital converter (ADC) having an input side coupled to the output side of the AFG circuit and an output side coupled to the input of the DSP, the output of the DSP being coupled to an input of the at least one xDSL modem.

20. The noise cancellation system of claim 16, wherein the signal provider comprises a communications service provider.