FEEDBACK ADAPTIVE NOISE CANCELLATION (ANC) CONTROLLER AND METHOD HAVING A FEEDBACK RESPONSE PARTIALLY PROVIDED BY A FIXED-RESPONSE FILTER

• US 20170053639A1
• Filed: 08/19/2016
• Published: 02/23/2017
• Est. Priority Date: 08/20/2015
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic International Semiconductor Ltd. (Cirrus Logic Incorporated)
• Inventors: Lu, Yang, Hellman, Ryan A., Zhou, Dayong
• Granted Patent: US 10,026,388 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G10K 11/17815 between the reference signals and the error signals, i.e. primary path
• CPC Class Codes: G10K 11/17817 between the output signals and the error signals, i.e. secondary path
• CPC Class Codes: G10K 11/17853 of the filter
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17857 Geometric disposition, e.g. placement of microphones
• CPC Class Codes: G10K 11/17881 the reference signal being an acoustic signal, e.g. recorded with a microphone
• 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 2210/108 Communication systems, e.g. where useful sound is kept and noise is cancelled
• CPC Class Codes: G10K 2210/1081 Earphones, e.g. for telephones, ear protectors or headsets
• CPC Class Codes: G10K 2210/3017 Copy, i.e. whereby an estimated transfer function in one functional block is copied to another block
• CPC Class Codes: G10K 2210/3026 Feedback
• CPC Class Codes: G10K 2210/3027 Feedforward
• CPC Class Codes: G10K 2210/3028 Filtering, e.g. Kalman filters or special analogue or digital filters
• CPC Class Codes: G10K 2210/3055 Transfer function of the acoustic system

Abstract

A controller for an adaptive noise canceling (ANC) system simplifies the design of a stable control response by making the ANC gain of the system independent of a secondary path extending from a transducer of the ANC system to a sensor of the ANC system that measures the ambient noise. The controller includes a fixed filter having a predetermined fixed response, and a variable filter coupled together. The variable response filter compensates for variations of a transfer function of a secondary path that includes at least a path from a transducer of the ANC system to a sensor of the ANC system, so that the ANC gain is independent of the variations in the transfer function of the secondary path.

Claims

1. An adaptive noise cancellation (ANC) controller, comprising:

a fixed filter having a predetermined fixed transfer function (B(z)) that relates to and maintains stability of a compensated feedback loop, wherein the fixed filter contributes to an ANC gain of an ANC system; and

a variable-response filter coupled to the fixed filter, wherein a response of the variable-response filter compensates for variations of a transfer function of a secondary path that includes at least a path from a transducer of the ANC system to a sensor of the ANC system, so that the ANC gain is independent of the variations in the transfer function of the secondary path.

2. The ANC controller of claim 1, wherein the fixed filter causes the ANC gain to be a uniform feedback gain that depends on the predetermined fixed transfer function.

3. The ANC controller according to claim 1, wherein the response of the variable-response filter is an inverse of the transfer function of the secondary path.

4. The ANC controller of claim 3, wherein the response of the variable response filter is controlled in conformity with a control output of an adaptive filter of the ANC system.

5. The ANC controller according to claim 4, wherein the variable-response filter is the adaptive filter, whereby the response of the variable-response filter is dependent on frequency content of a signal provided as an input to the variable response filter to which the response of the variable-response filter is applied.

6. The ANC controller according to claim 4, wherein the adaptive filter is an adaptive filter of a feed-forward portion of the ANC system that adapts to cancel the effects of the secondary path on a component of a signal reproduced by the transducer of the ANC system.

7. The ANC controller according to claim 1, wherein the sensor is a microphone and the transducer is a speaker.

8. An integrated circuit (IC) for implementing at least a portion of an audio device including acoustic noise canceling, the integrated circuit comprising:

an output for providing an output signal to an output transducer including an anti-noise signal for countering the effects of ambient audio sounds in an acoustic output of the transducer;

at least one microphone input for receiving at least one microphone signal indicative of the ambient audio sounds and that contains a component due to the acoustic output of the transducer; and

a processing circuit that adaptively generates the anti-noise signal to reduce the presence of the ambient audio sounds heard by the listener, wherein the processing circuit implements a feedback filter having a response that generates at least a portion of the anti-noise signal from the at least one microphone signal, the feedback filter comprising a fixed filter having a predetermined fixed transfer function (B(z)) and a variable-response filter coupled to the fixed filter, wherein a response of the variable-response filter compensates for variations of a transfer function of a secondary path that includes at least a path from the transducer to the at least one microphone.

9. The integrated circuit of claim 8, wherein the fixed filter causes an ANC gain of the system formed by the feedback filter, the transducer, the at least one microphone and the secondary path to be a uniform feedback gain that depends on the predetermined fixed transfer function.

10. The integrated circuit according to claim 8, wherein the response of the variable-response filter is an inverse of the transfer function of the secondary path.

11. The integrated circuit of claim 10, wherein the response of the variable response filter is controlled in conformity with a control output of an adaptive filter implemented by the processing circuit that models the secondary path.

12. The integrated circuit of claim 11, wherein the variable-response filter is the adaptive filter, whereby the response of the variable-response filter is dependent on frequency content of a signal provided as an input to the variable response filter to which the response of the variable-response filter is applied.

13. The integrated circuit of claim 11, wherein the processing circuit further implements a feed-forward adaptive filter that generates another portion of the anti-noise signal, and further implements a secondary path adaptive filter that adapts to cancel the effects of the secondary path on a component of a source audio signal reproduced by the transducer of the ANC system.

14. A method of canceling effects of ambient noise, the method comprising:

adaptively generating an anti-noise signal to reduce the presence of the ambient noise;

providing a result of the combining to a transducer;

measuring the ambient noise with at least one sensor;

filtering an output of the at least one sensor with a fixed filter having a predetermined fixed transfer function (B(z)) that relates to and maintains stability of a compensated feedback loop, wherein the fixed filter contributes to an ANC gain of an ANC system and a variable-response filter coupled to the fixed filter, wherein a response of the variable-response filter compensates for variations of a transfer function of a secondary path that includes at least a path from a transducer of the ANC system to a sensor of the ANC system, so that the ANC gain is independent of the variations in the transfer function of the secondary path.

15. The method of claim 14, wherein the filtering causes the ANC gain to be a uniform feedback gain that depends on the predetermined fixed transfer function.

16. The method of claim 14, wherein the response of the variable-response filter is an inverse of the transfer function of the secondary path.

17. The method of claim 16, further comprising controlling the response of the variable response filter in conformity with a control output of an adaptive filter of the ANC system.

18. The method of claim 17, wherein the variable-response filter is the adaptive filter, wherein the response of the variable-response filter controlled in dependence on frequency content of a signal provided as an input to the variable response filter to which the response of the variable-response filter is applied.

19. The method of claim 17, wherein the adaptive filter is an adaptive filter of a feed-forward portion of the ANC system that adapts to cancel the effects of the secondary path on a component of a signal reproduced by the transducer of the ANC system.

20. The method of claim 14, wherein the sensor is a microphone and the transducer is a speaker.