Systems and methods for maintaining playback fidelity in an audio system with adaptive noise cancellation

• US 9,620,101 B1
• Filed: 10/08/2013
• Issued: 04/11/2017
• Est. Priority Date: 10/08/2013
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Thandri, Bharath Kumar, Satoskar, Aniruddha, Alderson, Jeffrey D., Melanson, John L.
• Primary Examiner(s): Elahee, Md S
• Application Number:
  US14/048,485
• Time in Patent Office: 1,281 Days
• Field of Search: 381 716, 381 7111, 381120, 381121, 381123, 381150, 381323, 704255, 330151
• CPC Class Codes: G10K 11/17833 by using a self-diagnostic function or a malfunction prevention function, e.g. detecting abnormal output levels
• CPC Class Codes: G10K 11/1785 Methods, e.g. algorithms; Devices G10K11/1781, G10K11/1783 take precedence
• 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 2210/3212 Actuator details, e.g. composition or microstructure
• CPC Class Codes: H02M 3/07 using capacitors charged and discharged alternately by semiconductor devices with control electrode , e.g. charge pumps
• CPC Class Codes: H03F 1/0222 by using a signal derived from the input signal
• CPC Class Codes: H03F 1/26 Modifications of amplifiers to reduce influence of noise generated by amplifying elements
• CPC Class Codes: H03F 2200/507 A switch being used for switching on or off a supply or supplying circuit in an IC-block amplifier circuit
• CPC Class Codes: H03F 3/187 in integrated circuits
• CPC Class Codes: H03F 3/72 Gated amplifiers, i.e. amplifiers which are rendered operative or inoperative by means of a control signal

Abstract

An audio amplifier circuit may include a power amplifier, a charge pump power supply, and a control circuit. The power amplifier may have an audio input for receiving an audio input signal, an audio output for providing the output signal, and a power supply input. The charge pump power supply may provide a power supply voltage to the power supply input. The charge pump power supply may have a select input for selecting an operating mode of the power supply. In a first operating mode, the power supply voltage may equal to a first voltage, and in a second operating mode, the power supply voltage may be substantially equal to a second voltage which is a rational fraction of the first voltage. The control circuit may generate the select input based on a magnitude of anti-noise generated by an adaptive noise cancellation system associated with the audio transducer.

Claims

1. An audio amplifier circuit for providing an output signal to an audio transducer, the audio amplifier circuit comprising:

a power amplifier having an audio input for receiving an audio input signal, an audio output for providing the output signal, and a power supply input;

a charge pump power supply for providing a power supply voltage to the power supply input of the power amplifier, wherein;

the charge pump power supply has a select input for selecting an operating mode of the power supply; and

in a first operating mode, the power supply voltage is equal to a first voltage, and wherein in a second operating mode, the power supply voltage is substantially equal to a second voltage which is a rational fraction of the first voltage; and

a control circuit for generating the select input based on a magnitude of anti-noise generated by an adaptive noise cancellation system associated with the audio transducer.

2. The audio amplifier circuit of claim 1, further comprising an adaptive noise cancellation noise level estimation circuit for generating a noise advisory level signal based on:

a reference microphone signal indicative of ambient audio sounds in an acoustic output of the transducer; and

a gain input signal indicative of a signal gain of an adaptive filter having a response that generates an anti-noise signal from the reference microphone signal, wherein the anti-noise signal counters the effect of ambient audio sounds in the acoustic output of the transducer; and

wherein the control circuit generates the select input based on the noise advisory level signal.

3. The audio amplifier circuit of claim 1, wherein the control circuit further generates the select input based on a signal indicative of the magnitude of the output signal.

4. The audio amplifier circuit of claim 1, wherein the control circuit causes the charge pump power supply to transition from the second operating mode to the first operating mode responsive to a determination that a magnitude of the anti-noise signal is greater than a threshold magnitude.

5. The audio amplifier circuit of claim 4, wherein the threshold magnitude is based on the power supply voltage in the second operating mode.

6. The audio amplifier circuit of claim 1, wherein:

in a third operating mode, the power supply voltage is equal to a third voltage substantially equal to another rational fraction of the first voltage and less than the second voltage; and

wherein the control circuit causes the charge pump power supply to transition from the third operating mode to the first operating mode responsive to a determination that a magnitude of the anti-noise signal is greater than a threshold magnitude.

7. The audio amplifier circuit of claim 1, wherein:

the power supply input comprises a pair of power supply rail connections substantially symmetric about a reference potential; and

the power supply voltage provided by the charge pump power supply is a bi-polar power supply voltage having a first polarity and a second polarity across the pair of power supply rail connections of the power amplifier.

8. The audio amplifier circuit of claim 7, wherein:

the charge pump power supply has a signal polarity input for indicating a polarity of the output signal;

the charge pump power supply increases a magnitude of the first polarity of the power supply voltage and maintains a magnitude of the second polarity of the power supply voltage substantially constant responsive to the signal polarity input indicating a positive polarity of the output signal and a magnitude of the anti-noise signal is greater than a threshold magnitude; and

the charge pump power supply increases the magnitude of the second polarity of the power supply voltage and maintains the magnitude of the first polarity of the power supply voltage substantially constant responsive to the signal polarity input indicating a negative polarity of the output signal and the magnitude of the anti-noise signal is greater than a threshold magnitude.

9. The audio amplifier circuit of claim 1, wherein:

the charge pump power supply comprises a plurality of switches for switching one or more capacitors to provide the first polarity voltage and the second polarity voltage;

in normal operating mode, at least one switch of the plurality of switches has a first impedance and in a weak operating mode, the at least one switch has a second impedance greater than the first impedance; and

the control circuit causes the at least one switch to operate in the weak operating mode responsive to a determination that a magnitude of the anti-noise signal is lesser than a threshold magnitude and causes the at least one switch to operate in the normal operating mode responsive to a determination that the magnitude of the anti-noise signal is greater than the threshold magnitude.

10. The audio amplifier circuit of claim 1, further comprising a selectively enabled second charge pump power supply for generating current to the power supply input, wherein the control circuit enables the second charge pump power supply responsive to a determination that the noise advisory level signal indicates that a magnitude of the anti-noise signal is greater than the threshold magnitude and disables the second charge pump power supply responsive to a determination that the noise advisory level signal indicates that a magnitude of the anti-noise signal is lesser than a threshold magnitude.

11. An audio amplifier circuit for providing an output signal to an audio transducer, the audio amplifier circuit comprising:

a power amplifier having an audio input for receiving an audio input signal, an audio output for providing the output signal, and a power supply input;

a charge pump power supply for providing a power supply voltage to the power supply input of the power amplifier, wherein;

the charge pump power supply has a select input for selecting an operating mode of the power supply; and

in a first operating mode, the power supply voltage is equal to a first voltage, and wherein in a second operating mode, the power supply voltage is substantially equal to a second voltage which is a rational fraction of the first voltage;

a clip detection circuit for detecting the presence of clipping of the output signal and generating a clip detect signal based on the presence or absence of clipping; and

an adaptive noise cancellation circuit for generating an anti-noise signal for countering the effects of ambient sounds at an acoustic output of the audio transducer, the adaptive noise cancellation circuit having an adaptive filter for generating the anti-noise signal from a reference microphone signal indicative of ambient audio sounds, wherein the adaptive noise cancellation circuit selectively enables adaptation of the adaptive filter based on the clip detect signal.

12. A method for providing an output signal to an audio transducer, comprising:

providing by a charge pump power supply a power supply voltage to a power supply input of a power amplifier having an audio input for receiving an audio input signal and an audio output for providing the output signal, wherein;

the charge pump power supply has a select input for selecting an operating mode of the power supply; and

in a first operating mode, the power supply voltage is equal to a first voltage, and wherein in a second operating mode, the power supply voltage is substantially equal to a second voltage which is a rational fraction of the first voltage; and

generating the select input based on a magnitude of anti-noise generated by an adaptive noise cancellation system associated with the audio transducer.

13. The method of claim 12, further comprising:

generating a noise advisory level signal based on;

a reference microphone signal indicative of ambient audio sounds in an acoustic output of the transducer; and

a gain input signal indicative of a signal gain of an adaptive filter having a response that generates an anti-noise signal from the reference microphone signal, wherein the anti-noise signal counters the effect of ambient audio sounds in the acoustic output of the transducer; and

generating the select input based on the noise advisory level signal.

14. The method of claim 12, further comprising generating the select input based on a signal indicative of the magnitude of the output signal.

15. The method of claim 12, further comprising transitioning the charge pump power supply from the second operating mode to the first operating mode responsive to a determination that a magnitude of the anti-noise signal is greater than a threshold magnitude.

16. The method of claim 12, wherein the threshold magnitude is based on the power supply voltage in the second operating mode.

17. The method of claim 12, wherein in a third operating mode, the power supply voltage is equal to a third voltage substantially equal to another rational fraction of the first voltage and less than the second voltage, and the method further comprises transitioning the charge pump power supply from the third operating mode to the first operating mode responsive to a determination that a magnitude of the anti-noise signal is greater than a threshold magnitude.

18. The method of claim 12, wherein:

the power supply input comprises a pair of power supply rail connections substantially symmetric about a reference potential; and

the power supply voltage provided by the charge pump power supply is a bi-polar power supply voltage having a first polarity and a second polarity across the pair of power supply rail connections of the power amplifier.

19. The method of claim 18, wherein the charge pump power supply has a signal polarity input for indicating a polarity of the output signal, and the method further comprises:

increasing a magnitude of the first polarity of the power supply voltage and maintaining a magnitude of the second polarity of the power supply voltage substantially constant responsive to the signal polarity input indicating a positive polarity of the output signal and a magnitude of the anti-noise signal is greater than a threshold magnitude; and

increasing the magnitude of the second polarity of the power supply voltage and maintaining the magnitude of the first polarity of the power supply voltage substantially constant responsive to the signal polarity input indicating a negative polarity of the output signal and the magnitude of the anti-noise signal is greater than a threshold magnitude.

20. The method of claim 12, wherein:

the charge pump power supply comprises a plurality of switches for switching one or more capacitors to provide the first polarity voltage and the second polarity voltage; and

in a normal operating mode, at least one switch of the plurality of switches has a first impedance and in a weak operating mode, the at least one switch has a second impedance greater than the first impedance;

wherein the method further comprises operating the at least one switch in the weak operating mode responsive to a determination that a magnitude of the anti-noise signal is lesser than a threshold magnitude and operating the at least one switch in the normal operating mode responsive to a determination that the magnitude of the anti-noise signal is greater than the threshold magnitude.

21. The method of claim 12, further comprising:

enabling a selectively enabled second charge pump power supply for generating current to the power supply input responsive to a determination that the noise advisory level signal indicates that a magnitude of the anti-noise signal is greater than the threshold magnitude; and

disabling the second charge pump power supply responsive to a determination that the noise advisory level signal indicates that a magnitude of the anti-noise signal is lesser than a threshold magnitude.

22. A method for providing an output signal to an audio transducer, comprising:

providing a power supply voltage to a power supply input of a power amplifier having an audio input for receiving an audio input signal and an audio output for providing the output signal, wherein;

the charge pump power supply has a select input for selecting an operating mode of the power supply; and

in a first operating mode, the power supply voltage is equal to a first voltage, and wherein in a second operating mode, the power supply voltage is substantially equal to a second voltage which is a rational fraction of the first voltage;

detecting the presence of clipping of the output signal and generating a clip detect signal based on the presence or absence of clipping; and

based on the clip detect signal, enabling adaptation of an adaptive filter of an adaptive noise cancellation circuit for generating an anti-noise signal for countering the effects of ambient sounds at an acoustic output of the audio transducer, the adaptive filter for generating the anti-noise signal from a reference microphone signal indicative of ambient audio sounds.