Reduced delay digital active noise cancellation

• US 20120140942A1
• Filed: 12/21/2010
• Published: 06/07/2012
• Est. Priority Date: 12/01/2010
• Status: Active Grant

• Current Assignee: Dialog Semiconductor GmbH (Renesas Electronics Corporation)
• Original Assignee: Dialog Semiconductor GmbH (Renesas Electronics Corporation)
• Inventors: Loeda, Sebastian
• Granted Patent: US 8,953,813 B2
• Time in Patent Office: Days
• US Class Current: 381/71.11
• CPC Class Codes: G10K 11/17853 of the filter
• CPC Class Codes: G10K 11/17855 for improving speed or power requirements
• CPC Class Codes: G10K 11/17873 using a reference signal without an error signal, e.g. pure feedforward
• CPC Class Codes: G10K 11/17885 additionally using a desired external signal, e.g. pass-through audio such as music or speech
• CPC Class Codes: G10K 2210/1081 Earphones, e.g. for telephones, ear protectors or headsets
• CPC Class Codes: G10K 2210/3051 Sampling, e.g. variable rate, synchronous, decimated or interpolated
• CPC Class Codes: G10L 21/0208 Noise filtering

Abstract

A digital active noise cancellation circuit device (330) includes an oversampled, sigma-delta, A/D converter (204), a digital decimation filter (208), a digital intermediate filter (308), a digital interpolation filter (232), and a sigma-delta, D/A converter (252). The device (330) is operative to perform the steps of: receiving (904) the analog noise signal (64), converting (908) the analog noise signal into a digital noise signal (261); transferring (912) the digital noise signal to a digital decimation filter, selectively bypassing (916) at least a portion of the digital decimation filter by transferring the digital noise signal to a digital intermediate filter (304), processing (920) the digital noise signal in the digital intermediate filter to generate a digital anti-noise signal (316), transferring (1010) the digital anti-noise signal into a digital interpolation filter (232) operable to up-sample the digital anti-noise signal, selectively bypassing (1020) at least a portion of the digital interpolation filter and converting (1030) the digital anti-noise signal into an analog anti-noise signal (68).

Claims

1. A method for generating an anti-noise signal for a digital active noise cancellation circuit in a digital audio device, the method comprising:

receiving an analog noise signal;

converting the analog noise signal into a digital noise signal by an oversampled, sigma-delta, A/D converter;

transferring the digital noise signal to a digital decimation filter operable to down-sample the digital noise signal;

selectively bypassing at least a portion of the digital decimation filter by transferring the digital noise signal to a digital intermediate filter; and

processing the digital noise signal in the digital intermediate filter to generate a digital anti-noise signal.

2. The method of claim 1 further comprising the steps of:

transferring the digital anti-noise signal into a digital interpolation filter operable to up-sample the digital anti-noise signal;

selectively bypassing at least a portion of the digital interpolation filter; and

converting the digital anti-noise signal into an analog anti-noise signal by a sigma-delta, D/A converter.

3. The method of claim 2 wherein the digital noise signal is transferred directly from the A/D converter to the digital intermediate filter and the digital anti-noise signal is transferred directly from the digital intermediate filter to the D/A converter.

4. The method of claim 3 wherein the digital interpolation filter comprises a plurality of FIR filters, an up-sampler, and a sigma-delta modulator.

5. The method of claim 4 wherein the digital noise signal is transferred directly from the A/D converter to the digital intermediate filter and the digital anti-noise signal is transferred directly from the digital intermediate filter to the sigma-delta modulator.

6. The method of claim 4 wherein the digital noise signal is transferred directly from the A/D converter to the digital intermediate filter and the digital anti-noise signal is transferred directly from the digital intermediate filter to the up-sampler.

7. The method of claim 2 wherein the digital decimation filter comprises a CIC filter and a plurality of FIR filters.

8. The method of claim 7 wherein the digital noise signal is transferred from a stage of the CIC filter to the digital intermediate filter and the digital anti-noise signal is transferred directly to the D/A converter.

9. The method of claim 7 wherein the digital noise signal is transferred from one of the FIR filters to the digital intermediate filter and the digital anti-noise signal is transferred directly to the D/A converter.

10. The method of claim 2 wherein the digital interpolation filter comprises a plurality of FIR filters, an up-sampler, and a sigma-delta modulator and wherein the digital decimation filter comprises a CIC filter and a plurality of FIR filters.

11. The method of claim 1 further comprising the steps of:

combining the digital anti-noise signal with a digital audio input signal to generate a digital combined audio signal;

transferring the digital combined audio signal into a digital interpolation filter operable to up-sample the digital combined audio signal;

selectively bypassing at least a portion of the digital interpolation filter; and

converting the digital combined audio signal into an analog combined audio signal by a sigma-delta, D/A converter.

12. A digital audio device enabled for active noise cancellation comprising:

a digital active noise cancellation circuit operatively coupled to the digital audio circuit comprising;

an oversampled, sigma-delta, A/D converter;

a digital decimation filter;

a digital intermediate filter;

a digital interpolation filter; and

a sigma-delta, D/A converter;

wherein the digital active noise cancellation circuit is operative to perform the steps of;

receiving the analog noise signal;

converting the analog noise signal into a digital noise signal by an oversampled, sigma-delta, analog-to-digital converter;

transferring the digital noise signal to a digital decimation filter operable to down-sample the digital noise signal;

selectively bypassing at least a portion of the digital decimation filter by transferring the digital noise signal to a digital intermediate filter; and

processing the digital anti-noise signal in the digital intermediate filter to generate a digital anti-noise signal; and

a digital audio circuit operative to combine an audio signal with an analog anti-noise signal and to amplify the combined signals through a speaker.

13. The device of claim 12 wherein the digital active noise cancellation circuit is further operative to perform the steps of:

transferring the digital anti-noise signal into a digital interpolation filter operable to up-sample the digital anti-noise signal;

selectively bypassing at least a portion of the digital interpolation filter; and

converting the digital anti-noise signal into an analog anti-noise signal by a sigma-delta, D/A converter.

14. The device of claim 13 wherein the digital anti-noise circuit is further operative to transfer the digital noise signal directly from the A/D converter to the digital intermediate filter and to transfer the digital anti-noise signal directly from the digital intermediate filter to the D/A converter

15. The device of claim 13 wherein the digital interpolation filter comprises a plurality of FIR filters, an up-sampler, and a sigma-delta modulator.

16. The device of claim 15 wherein the digital noise signal is transferred directly from the A/D converter to the digital intermediate filter and the digital anti-noise signal is transferred directly from the digital intermediate filter to the sigma-delta modulator.

17. The device of claim 15 wherein the digital noise signal is transferred directly from the A/D converter to the digital intermediate filter and the digital anti-noise signal is transferred directly from the digital intermediate filter to the up-sampler.

18. The device of claim 13 wherein the digital decimation filter comprises a CIC filter and a plurality of FIR filters.

19. The device of claim 18 wherein the digital noise signal is transferred from a stage of the CIC filter to the digital intermediate filter and the digital anti-noise signal is transferred directly to the D/A converter.

20. The device of claim 18 wherein the digital noise signal is transferred from one of the FIR filters to the digital intermediate filter and the digital anti-noise signal is transferred directly to the D/A converter.

21. The device of claim 13 wherein the digital interpolation filter comprises a plurality of FIR filters, an up-sampler, and a sigma-delta modulator and wherein the digital decimation filter comprises a CIC filter and a plurality of FIR filters.

22. The device of claim 12 wherein the digital active noise cancellation circuit is further operative to perform the steps of:

combining the digital anti-noise signal with a digital audio input signal to generate a digital combined audio signal;

transferring the digital combined audio signal into a digital interpolation filter operable to up-sample the digital combined audio signal;

selectively bypassing at least a portion of the digital interpolation filter; and

converting the digital combined audio signal into an analog combined audio signal by a sigma-delta, D/A converter.

23. A digital active noise cancellation circuit device comprising:

an oversampled, sigma-delta, A/D converter;

a digital decimation filter;

a digital intermediate filter;

a digital interpolation filter; and

a sigma-delta, D/A converter;

wherein the digital active-noise cancellation circuit device is operative to perform the steps of;

receiving the analog noise signal;

converting the analog noise signal into a digital noise signal by an oversampled, sigma-delta, analog-to-digital converter;

transferring the digital noise signal to a digital decimation filter operable to down-sample the digital noise signal;

selectively bypassing at least a portion of the digital decimation filter by transferring the digital noise signal to a digital intermediate filter; and

processing the digital noise signal in the digital intermediate filter to generate a digital anti-noise signal.

24. The device of claim 23 wherein the digital active noise cancellation circuit device is further operative to perform the steps of:

transferring the digital anti-noise signal into a digital interpolation filter operable to up-sample the digital anti-noise signal;

selectively bypassing at least a portion of the digital interpolation filter; and

converting the digital anti-noise signal into an analog anti-noise signal by a sigma-delta, D/A converter.

25. The device of claim 24 wherein the digital anti-noise circuit is further operative to transfer the digital noise signal directly from the A/D converter to the digital intermediate filter and to transfer the digital anti-noise signal directly from the digital intermediate filter to the D/A converter

26. The device of claim 24 wherein the digital interpolation filter comprises a plurality of FIR filters, an up-sampler, and a sigma-delta modulator.

27. The device of claim 26 wherein the digital noise signal is transferred directly from the A/D converter to the digital intermediate filter and the digital anti-noise signal is transferred directly from the digital intermediate filter to the sigma-delta modulator.

28. The device of claim 26 wherein the digital noise signal is transferred directly from the A/D converter to the digital intermediate filter and the digital anti-noise signal is transferred directly from the digital intermediate filter to the up-sampler.

29. The device of claim 24 wherein the digital decimation filter comprises a CIC filter and a plurality of FIR filters.

30. The device of claim 24 wherein the digital interpolation filter comprises a plurality of FIR filters, an up-sampler, and a sigma-delta modulator and wherein the digital decimation filter comprises a CIC filter and a plurality of FIR filters.

31. The device of claim 23 wherein the digital active noise cancellation circuit device is further operative to perform the steps of:

combining the digital anti-noise signal with a digital audio input signal to generate a digital combined audio signal;

transferring the digital combined audio signal into a digital interpolation filter operable to up-sample the digital combined audio signal;

selectively bypassing at least a portion of the digital interpolation filter; and

converting the digital combined audio signal into an analog combined audio signal by a sigma-delta, D/A converter.