Nonlinear Distortion Compensation for Capacitive MEMS Microphones

1 . A method comprising:

receiving a signal corresponding to an input sound pressure detected by a capacitive microelectromechanical system (MEMS) microphone, wherein the capacitive MEMS microphone includes an active capacitance, and wherein a nonlinear relationship exists between the signal and the input sound pressure;

determining, based on the signal, an input parameter associated with the active capacitance;

determining an output signal based on the input parameter, wherein the output signal and the input sound pressure have a linear relationship;

compensating the signal, based on the determined output signal, to have the linear relationship with the input sound pressure; and

outputting the compensated signal.

2 . The method of claim 1 , further comprising identifying the nonlinear relationship between the signal and the input sound pressure based on a sound level of the signal being higher than a threshold value.

3 . The method of claim 1 , wherein the input parameter is a normalized displacement (b) of a movable electrode in the active capacitance corresponding to the input sound pressure.

4 . The method of claim 3 , wherein:

b

=

-

v

⁡

(

1

+

α

)

v

⁢

α

-

V

b

,

α

=

C

p

/

C

e

,

C p is the parasitic capacitance,

C e is the active capacitance; and

V b is a bias voltage on C e .

5 . The method of claim 4 , wherein the determining the output signal, based on the input parameter, comprises:

estimating the input sound pressure (p) based on the normalized displacement; and

determining the output signal by multiplying p by a transfer function (TF).

6 . The method of claim 4 , wherein the determining the output signal, based on the input parameter, comprises multiplying the normalized dis lacement by a transfer function (TF) to obtain the output signal, wherein

TF

′

=

V

b

1

+

α

.

7 . The method of claim 1 , wherein the MEMS microphone includes a MEMS transducer.

8 . A computer-readable storage medium storing instructions that, when executed by a computing system, cause the computing system to:

receive a signal corresponding to an input sound pressure detected by a capacitive microelectromechanical system (MEMS) microphone, wherein the capacitive MEMS microphone includes an active capacitance, and wherein a nonlinear relationship exists between the signal and the input sound pressure;

determine, based on the signal, an input parameter associated with the active capacitance;

determine an output signal based on the input parameter, wherein the output signal and the input sound pressure have a linear relationship;

compensate the signal, based on the determined output signal, to have the linear relationship with the input sound pressure; and

output the compensated signal.

9 . The computer-readable storage medium of claim 8 , wherein the instructions, when executed, further cause the computing system to identify the nonlinear relationship between the signal and the input sound pressure based on a sound level of the signal being higher than a threshold value.

10 . The computer-readable storage medium of claim 8 , wherein the input parameter is a normalized displacement (b) of a movable electrode in the active capacitance corresponding to the input sound pressure.

11 . The computer-readable storage medium of claim 10 , wherein:

b

=

-

v

⁡

(

1

+

α

)

v

⁢

α

-

V

b

,

α

=

C

p

/

C

e

,

C p is the parasitic capacitance,

C e is the active capacitance; and

V b is a bias voltage on C e .

12 . The computer-readable storage medium of claim 11 , wherein the determining the output signal, based on the input parameter, comprises:

estimating the input sound pressure (p) based on the normalized displacement; and

determining the output signal by multiplying p by a transfer function (TF).

13 . The computer-readable storage medium of claim 11 , wherein the determining the output signal, based on the input parameter, comprises multiplying the normalized displacement by a transfer function (TF) to obtain the output signal, wherein

TF

′

=

V

b

1

+

α

.

14 . The computer-readable storage medium of claim 8 , wherein the MEMS microphone includes a MEMS transducer.

15 . An audio system comprising:

a capacitive microelectromechanical system (MEMS) microphone, wherein the capacitive MEMS microphone includes an active capacitance;

a controller configured to:

receive a signal corresponding to an input sound pressure detected by the capacitive microelectromechanical system (MEMS) microphone, wherein a nonlinear relationship exists between the signal and the input sound pressure;

determine, based on the signal, an input parameter associated with the active capacitance;

determine an output signal based on the input parameter, wherein the output signal and the input sound pressure have a linear relationship; and

compensate the signal, based on the determined output signal, to have the linear relationship with the input sound pressure; and

a speaker configured to output the compensated signal.

16 . The audio system of claim 15 , wherein the controller is further configured to identify the nonlinear relationship between the signal and the input sound pressure based on a sound level of the signal being higher than a threshold value.

17 . The audio system of claim 15 , wherein the input parameter is a normalized displacement (b) of a movable electrode in the active capacitance corresponding to the input sound pressure.

18 . The audio system of claim 17 , wherein:

b

=

-

v

⁡

(

1

+

α

)

v

⁢

α

-

V

b

,

α

=

C

p

/

C

e

,

C p is the parasitic capacitance,

C e is the active capacitance; and

V b is a bias voltage on C e .

19 . The audio system of claim 18 , wherein the determining the output signal, based on the input parameter, comprises multiplying the normalized displacement by a transfer function (TF) to obtain the output signal, wherein

TF

′

=

V

b

1

+

α

.

20 . The audio system of claim 15 , wherein the MEMS microphone includes a MEMS transducer.