Noise cancellation device and noise cancellation method

1. A noise cancellation device, comprising:

an anti-noise filter circuit configured to provide a corresponding one of transfer functions to process a digital signal, in order to generate a noise cancellation signal, wherein the transfer functions are different from each other;

an output circuit configured to mix the noise cancellation signal, a reference signal, and an input signal to generate a mixed signal, and configured to generate a sound output signal based on the mixed signal, wherein the digital signal is associated with the sound output signal; and

a detection circuit configured to control the anti-noise filter circuit to provide the corresponding one of the transfer functions according to a comparison result of a first ratio and a first threshold value,

wherein the first ratio is a ratio of a first power of the mixed signal to a second power of the digital signal.

2. The noise cancellation device of claim 1 , wherein the transfer functions comprise a first transfer function and a second transfer function, a voltage gain of the first transfer function is higher than a voltage gain of the second transfer function, and wherein

if the first ratio is greater than the first threshold value, the anti-noise filter circuit is configured to provide the first transfer function, and if the first ratio is less than the first threshold value, the anti-noise filter circuit is configured to provide the second transfer function.

3. The noise cancellation device of claim 2 , wherein the detection circuit is configured to determine that the noise cancellation device is in an on-ear position if the first ratio is greater than the first threshold value, and is configured to determine that the noise cancellation device is in an off-ear position if the first ratio is less than the first threshold value.

4. The noise cancellation device of claim 2 , further comprising:

a first analog-to-digital converter configured to convert a first electrical signal to the digital signal, wherein the first electrical signal is associated with the sound output signal and a noise signal.

5. The noise cancellation device of claim 4 , wherein the detection circuit is further configured to compare a second ratio with a second threshold value, in order to control the anti-noise filter circuit to provide the second transfer function if the second ratio is less than the second threshold value,

wherein the second ratio is ratio of a third power of the reference signal to a fourth power of the noise signal, and

the detection circuit is further configured to compare the first ratio with the first threshold value if the second ratio is greater than the second threshold value.

6. The noise cancellation device of claim 5 , wherein the detection circuit comprises:

a plurality of bandpass filters configured to process the mixed signal, the digital signal, and a digital noise signal, respectively, wherein the digital noise signal is used to estimate a power of the noise signal;

a plurality of power estimator circuits configured to determine the first power, the second power, the third power, and the fourth power according to the processed mixed signal, the processed digital signal, the reference signal, and the processed digital noise signal, respectively; and

a logic circuit configured to determine the first ratio according to the first power and the second power, and to determine the second ratio according to the third power and the fourth power,

wherein the logic circuit is further configured to compare the first ratio with the first threshold value, and to compare the second ratio and the second threshold value, in order to control the anti-noise filter circuit.

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

a second analog-to-digital converter configured to convert a second electrical signal to the digital noise signal.

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

a first audio-to-electric conversion device configured to receive the sound output signal and the noise signal and to generate the first electrical signal; and

a second audio-to-electric conversion device configured to receive the noise signal and to generate the second electrical signal.

9. The noise cancellation device of claim 5 , wherein the reference signal has an enabling period and a disabling period, and the detection circuit comprises:

a plurality of bandpass filters configured to process the mixed signal and the digital signal, respectively;

a first power estimator circuit configured to, according to the processed mixed signal, determine the first power during the enabling period;

a second power estimator circuit configured to, according to the processed digital signal, determine the second power during the enabling period, and to, according to the processed digital signal, determine the fourth power during the disabling period;

a third power estimator circuit configured to, according to the reference signal, determine the third power during the enabling period; and

a logic circuit configured to determine the first ratio according to the first power and the second power, and to determine the second ratio according to the third power and the fourth power,

wherein the logic circuit is further configured to compare the first ratio and the first threshold value, and to compare the second ratio with the second threshold value, in order to control the anti-noise filter circuit.

10. The noise cancellation device of claim 1 , wherein the output circuit comprises:

an arithmetic circuit configured to mix the noise cancellation signal, the reference signal, and the input signal to generate the mixed signal;

a digital-to-analog converter configured to convert the mixed signal; and

an electric-to-audio conversion device configured to output the sound output signal according to the converted mixed signal.

11. A noise cancellation method, comprising:

controlling an anti-noise filter circuit to provide a corresponding one of transfer functions to process a digital signal, in order to generate a noise cancellation signal, wherein the transfer functions are different from each other;

mixing the noise cancellation signal, a reference signal, and an input signal to generate a mixed signal, and generating a sound output signal based on the mixed signal, wherein the digital signal is associated with the sound output signal; and

controlling the anti-noise filter circuit to provide the corresponding one of the transfer functions according to a comparison result of a first ratio and a first threshold value,

wherein the first ratio is a ratio of a first power of the mixed signal to a second power of the digital signal.

12. The noise cancellation method of claim 11 , wherein the transfer functions comprise a first transfer function and a second transfer function, a voltage gain of the first transfer function is higher than a voltage gain of the second transfer function, and the controlling an anti-noise filter circuit to provide a corresponding one of transfer functions comprises:

providing the first transfer function if the first ratio is greater than the first threshold value; and

providing the second transfer function if the first ratio is less than the first threshold value.

13. The noise cancellation method of claim 12 , wherein an on-ear position is determined if the first ratio is greater than the first threshold value, and an off-ear position is determined if the first ratio is less than the first threshold value.

14. The noise cancellation method of claim 12 , further comprising:

converting a first electrical signal to the digital signal, wherein the first electrical signal is associated with the sound output signal and a noise signal.

15. The noise cancellation method of claim 14 , further comprising:

comparing a second ratio with a second threshold value, in order to control the anti-noise filter circuit to provide the second transfer function if the second ratio is less than the second threshold value, wherein the second ratio is a ratio of a third power of the reference signal to a fourth power of the noise signal; and

comparing the first ratio with the first threshold value of the second ratio is greater than the first threshold value.

16. The noise cancellation method of claim 15 , wherein controlling the anti-noise filter circuit to provide the corresponding one of the transfer functions according to the comparison result comprises:

processing, by a plurality of bandpass filters, the mixed signal, the digital signal, and a digital noise signal, respectively, wherein the digital noise signal is used to estimate a power of the noise signal;

determining the first power, the second power, the third power, and the fourth power according to the processed mixed signal, the processed digital signal, the reference signal, and the processed digital noise signal, respectively;

determining the first ratio according to the first power and the second power, and determining the second ratio according to the third power and the fourth power; and

comparing the first ratio with the first threshold value, and comparing the second ratio and the second threshold value, in order to control the anti-noise filter circuit.

17. The noise cancellation method of claim 16 , further comprising:

converting a second electrical signal to the digital noise signal.

18. The noise cancellation method of claim 17 , further comprising:

receiving, by a first audio-to-electric conversion device, the sound output signal and the noise signal, and generating the first electrical signal; and

receiving, by a second audio-to-electric conversion device, the noise signal, and generating the second electrical signal.

19. The noise cancellation method of claim 15 , wherein the reference signal has an enabling period and a disabling period, and controlling the anti-noise filter circuit to provide the corresponding one of the transfer functions according to the comparison result comprises:

processing, by a plurality of bandpass filters, the mixed signal and the digital signal, respectively;

determining the first power according to the processed mixed signal during the enabling period;

determining the second power according to the processed digital signal, during the enabling period;

determining the third power according to the reference signal during the enabling period;

determining the fourth power according to the processed digital signal during the disabling period;

determining the first ratio according to the first power and the second power, and determining the second ratio according to the third power and the fourth power; and

comparing the first ratio with the first threshold value, and comparing the second ratio with the second threshold value, in order to control the anti-noise filter circuit.

20. The noise cancellation method of claim 11 , wherein generating the sound output signal comprises:

mixing the noise cancellation signal, the reference signal, and the input signal to generate the mixed signal;

converting the mixed signal; and

outputting, by an electric-to-audio conversion device, the sound output signal according to the converted mixed signal.