Amplifier capable of controlling cut-off frequency in real time and amplification method for controlling cut-off frequency in real time

1. An amplifier of a digital audio amplifier capable of driving a loudspeaker using an input digital audio signal, the amplifier comprising:

a variable high-pass filter unit configured to filter the input digital audio signal according to a cut-off frequency Fc;

a displacement detector configured to detect in real time a displacement of the loudspeaker from an output digital audio signal outputted from the variable high-pass filter unit;

a controller configured to control the cut-off frequency Fc of the variable high-pass filter unit in real time according to the displacement detected by the displacement detector,

a first bypass path configured to bypass the input digital audio signal; and

a first switch configured to select and output one of the input digital audio signal bypassed by the first bypass path and the output digital audio signal of the variable high-pass filter unit.

2. The amplifier in accordance with claim 1 , wherein the variable high-pass filter unit comprises a first variable high-pass filter and a second variable high-pass filter in cascade, and wherein the input digital audio signal is sequentially high-pass filtered by the first variable high-pass filter and the second variable high-pass filter.

3. The amplifier in accordance with claim 2 , wherein the variable high-pass filter unit further comprises: a second bypass path configured to bypass an output signal of the first variable high-pass filter; and a second switch configured to select and output one of the output signal of the first variable high-pass filter bypassed by the second bypass path and an output signal of the second variable high-pass filter.

4. The amplifier in accordance with claim 1 , wherein the variable high-pass filter comprises a first variable high-pass filter and a second variable high-pass filter in cascade.

5. The amplifier in accordance with claim 4 , wherein the controller is configured to control in real time the cut-off frequency Fc of each of the first variable high-pass filter and the second variable high-pass filter according to the displacement detected in real time by the displacement detector.

6. The amplifier in accordance with claim 1 , wherein the displacement detector comprises a biquad filter.

7. The amplifier in accordance with claim 1 , wherein the controller is configured to increase the cut-off frequency Fc when the displacement detected by the displacement detector is greater than a reference value and to decrease the cut-off frequency Fc when the displacement detected by the displacement detector is smaller than the reference value.

8. An amplification method performed in a digital audio amplifier capable of driving a loudspeaker using an input digital audio signal, the method comprising:

(a) high-pass filtering the input digital audio signal according to a cut-off frequency Fc;

(b) detecting in real time a displacement of the loudspeaker from an output digital audio signal obtained by filtering the input digital audio signal in the step (a); and

(c) controlling the cut-off frequency Fc in real time according to the displacement detected in the step (b); and

(d) selecting and outputting one of the input digital audio signal and the output digital audio signal obtained by filtering the input digital audio signal in the step (a).

9. The amplification method in accordance with claim 8 , wherein the step (a) comprises:

(a-1) high-pass filtering the input digital audio signal according to the cut-off frequency Fc by passing the input digital audio signal through a first variable high-pass filter to generate an output signal; and

(a-2) high-pass filtering the output signal generated in the step (a-1) according to the cut-off frequency Fc by passing the output signal through a second variable high-pass filter to generate the output digital audio signal.

10. The amplification method in accordance with claim 9 , further comprising selecting and outputting one of the output signal and the output digital audio signal obtained by filtering the output signal in the step (a-2).

11. The amplification method in accordance with claim 9 , wherein the step (c) comprises controlling the cut-off frequency Fc in real time in the steps (a-1) and (a-2) according to the displacement detected in the step (b) in real time.

12. The amplification method in accordance with claim 8 , wherein the step (b) comprises detecting in real time the displacement of the loudspeaker by biquad-filtering the output digital audio signal obtained by filtering the input digital audio signal in the step (a).

13. The amplification method in accordance with claim 8 , wherein the step (c) comprises increasing the cut-off frequency Fc when the displacement detected by the step (b) is greater than a reference value and decreasing the cut-off frequency Fc when the displacement detected in the step (b) is smaller than the reference value.