Method and apparatus for amplifying audio signal

This application claims priority from Korean Patent Application No. 10-2010-0001899, filed on Jan. 8, 2010, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

1. Field

The present disclosure relates to a device for amplifying an audio signal and a method thereof.

2. Description of the Related Art

Conventional audio signal amplifying devices modulate an audio signal using a carrier wave. Conventionally, the modulated signal, which is generated by using the carrier wave, is amplified. Then, a demodulation operation is performed on the amplified modulated signal, using a demodulation filter, so that the carrier wave element included in the amplified modulated signal is eliminated. At this time, as the intensity of voltage and current of the amplified modulated signal is increased, the demodulation filter becomes larger. Accordingly, the size and power consumption of the audio signal amplifying device are increased.

The present disclosure provides a device for amplifying an audio signal and a method thereof.

According to an exemplary embodiment, there is provided an audio signal amplifying device, including a receiving unit that receives an audio signal; a carrier wave generation unit that generates first, second, third, and fourth carrier waves, the first, second, third, and fourth carrier waves having phases that are different from one another; an amplified modulation signal generation unit that compares the first carrier wave and the second carrier wave to the audio signal, respectively, generates a first modulation signal and a second modulation signal, respectively, based on results of the comparisons, amplifies the first modulation signal and the second modulation signal, respectively, based on a value of a first power supply voltage, and generates a first amplified modulation signal and a second amplified modulation signal from the amplified first modulation signal and the amplified second modulation signal, respectively; a first output unit that outputs a first output, the first output comprising one of the first amplified modulation signal or a second power supply voltage, according to a logic state of a third modulation signal, the third modulation signal generated from a result of comparing the third carrier wave to the audio signal; a second output unit that outputs a second output, the second output comprising one of the second amplified modulation signal or the second power supply voltage, according to a logic state of a fourth modulation signal, the fourth modulation signal generated from a result of comparing the fourth carrier wave to the audio signal; and a final output unit that synthesizes the first output and the second output, and outputs the synthesized signal.

Each of the first and the second amplified modulation signals may have a first voltage period having a first logic state and a second voltage period having a second logic state, and a portion of the first voltage period of the first amplified modulation signal is overlapped by a portion of the first voltage period of the second amplified modulation signal.

The carrier wave generation unit may generate the first carrier wave, and may generate the first carrier wave, and generates the second, the third, and the fourth carrier waves by shifting a phase of the first carrier wave.

A phase difference between the first and the second carrier waves may be 180 degrees, and a phase difference between the third and the fourth carrier waves may be 180 degrees.

The first and second modulation signals may be Pulse Width Modulation (PWM) signals.

The first and the second power supply voltage may have absolute voltage values that are equal to each other.

The audio signal amplifying device may further include a demodulation filter that demodulates the first output and the second output, wherein the final output unit may synthesize the demodulated first output and the demodulated second output, and outputs the synthesized signal.

The final output unit may invert a sign of the second, and synthesize the inverted second output and the first output, and output the synthesized signal.

According to another exemplary embodiment, there is provided a method of amplifying an audio signal, including receiving an audio signal; generating first, second, third, and fourth carrier waves, the first, second, third, and fourth carrier waves having phases that are different from one another; comparing the first carrier wave and the second carrier wave to the audio signal, respectively; generating a first modulation signal and a second modulation signal, respectively, based on results of the comparing; amplifying the first modulation signal and the second modulation signal, respectively, based on a value of a first power supply voltage; generating a first amplified modulation signal and a second amplified modulation signal from the amplified first modulation signal and the amplified second modulation signal, respectively; outputting a first output, the first output comprising one of the first amplified modulation signal or a second power supply voltage, according to a logic state of a third modulation signal, the third modulation signal generated from a result of comparing the third carrier wave to the audio signal; outputting a second output, the second output comprising one of the second amplified modulation signal or the second power supply voltage, according to a logic state of a fourth modulation signal, the fourth modulation signal generated from a result of comparing the fourth carrier wave to the audio signal; synthesizing the first output value and the second output value to generate a synthesized signal; and outputting the synthesized signal.

According to another exemplary embodiment, there is provided a computer-readable recording medium storing a program for performing a method of amplifying an audio signal, including receiving an audio signal; generating first, second, third, and fourth carrier waves, the first, second, third, and fourth carrier waves having phases that are different from one another; comparing the first carrier wave and the second carrier wave to the audio signal, respectively; generating a first modulation signal and a second modulation signal, respectively, based on results of the comparing; amplifying the first modulation signal and the second modulation signal, respectively, based on a value of a first power supply voltage; generating a first amplified modulation signal and a second amplified modulation signal from the amplified first modulation signal and the amplified second modulation signal, respectively; outputting a first output, the first output comprising one of the first amplified modulation signal or a second power supply voltage, according to a logic state of a third modulation signal, the third modulation signal generated from a result of comparing the third carrier wave to the audio signal; outputting a second output, the second output comprising one of the second amplified modulation signal or the second power supply voltage, according to a logic state of a fourth modulation signal, the fourth modulation signal generated from a result of comparing the fourth carrier wave to the audio signal; synthesizing the first output value and the second output value to generate a synthesized signal; and outputting the synthesized signal.

The above and other features and advantages will become more apparent by describing in detail exemplary embodiments thereof, with reference to the attached drawings in which:

FIG. 1 is a diagram illustrating an audio signal amplifying device according to an exemplary embodiment;

FIG. 2 is a diagram illustrating an audio signal amplifying device according to another exemplary embodiment;

FIG. 3 is a diagram illustrating an audio signal amplifying device according to another exemplary embodiment;

FIG. 4A is a diagram illustrating the voltage values of the signals inputted to the demodulation filters of the conventional audio signal amplifying device;

FIG. 4B is a diagram illustrating the voltage values of the signals inputted to the demodulation filters of the audio signal amplifying device according to an exemplary embodiment; and

FIG. 5 is a flowchart illustrating a method of amplifying the audio signal according an exemplary embodiment.

The present disclosure will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments are shown.

FIG. 1 is a diagram illustrating an audio signal amplifying device according to an exemplary embodiment.

Referring to FIG. 1 , an audio signal amplifying device 100 according to the exemplary embodiment includes a receiving unit 110 , a carrier wave generation unit 120 , an amplified modulation signal generation unit 130 , a first output unit 142 , a second output unit 144 and a final output unit 150 .

The receiving unit 110 receives an audio signal A 0 .

The carrier wave generation unit 120 generates first to fourth carrier waves C 1 to C 4 , whose phases are different from one another.

For instance, the carrier wave generation unit 120 may generate the first carrier wave C 1 , and then generate the second to the fourth carrier waves C 2 to C 4 by shifting a phase of the first carrier wave C 1 , for example, by 180 degrees, 90 degrees, and 270 degrees respectively.

The amplified modulation signal generation unit 130 generates a first amplified modulation signal MA 1 and a second amplified modulation signal MA 2 by amplifying a first modulation signal M 1 and a second modulation signal M 2 , respectively, based on a voltage value of a first power supply voltage P 1 . Herein, the first and the second modulation signals M 1 and M 2 are respective results of comparing the first and the second carrier waves C 1 and C 2 with the audio signal A 0 .

For instance, when the amplified modulation signal generation unit 130 generates the first modulation signal M 1 , the amplified modulation signal generation unit 130 may generate the first modulation signal M 1 in such a manner that the first modulation M 1 has a low level while the voltage value of the first carrier wave C 1 is equal to or lower than that of the audio signal A 0 at a time domain, and has a high level while the voltage value of the first carrier wave C 1 is higher than that of the audio signal A 0 . At this time, the low level state of the first modulation signal M 1 means that the voltage value of the first modulation signal M 1 is smaller than a predetermined critical value, and the high level state of the first modulation signal M 1 means that the voltage value of the first modulation signal M 1 is equal to or larger than the predetermined critical value.

If the first modulation signal M 1 is generated as discussed above, the voltage value of the first modulation signal M 1 is amplified to that of the first power supply voltage P 1 , and thus the first amplified modulation signal MA 1 is generated. In the same manner, the second amplified modulation signal MA 2 is generated. At this time, at the time domain, a time period where each of the first and the second amplified modulation signals MA 1 and MA 2 has the voltage value of the first power supply voltage P 1 is termed a first voltage period. A time period where each of the first and the second amplified modulation signals MA 1 and MA 2 has 0V is termed a second voltage period. Then, the first and the second amplified modulation signals MA 1 and MA 2 are generated in such a manner that a portion of the first voltage period of the first amplified modulation signal MA 1 is overlapped by a portion of the first voltage period of the second amplified modulation signal MA 2 .

For instance, when a portion of the first voltage period of the first amplified modulation signal MA 1 is from 0 ms to 100 ms, a portion of the first voltage period of the second amplified modulation signal MA 2 may be from 50 ms to 100 ms. If the first amplified modulation signal MA 1 is synthesized with the second amplified modulation signal MA 2 at the time period from 0 ms to 50 ms, the synthesized signal has the voltage value of the first power supply voltage P 1 . However, if the first amplified modulation signal MA 1 is synthesized with the second amplified modulation signal MA 2 at the time period from 50 ms to 100 ms, the synthesized signal has double of the voltage value of the first power supply voltage P 1 . In the exemplary embodiment, the first and the second amplified modulation signals MA 1 and MA 2 are not synthesized with each other, and the first and the second amplified modulation signals MA 1 and MA 2 are output to the first output unit 142 and the second output unit 144 , respectively.

In the above method, the phases of the first and the second carrier waves C 1 and C 2 , which are used for generating the first and the second modulation signals M 1 and M 2 , may have been determined differently. Accordingly, the first and the second amplified modulation signals MA 1 and MA 2 may be generated in such a manner that the portion of the portion of the first voltage period of the first amplified modulation signal MA 1 is overlapped by the portion of the first voltage period of the second amplified modulation signal MA 2 .

Meanwhile, in another exemplary embodiment, it may be checked whether the maximum voltage value of the audio signal A 0 is equal to or lower than the critical value. In the case where the maximum voltage value of the audio signal A 0 is equal to or lower than the critical value, the amplified modulation signal generation unit 130 may output two voltages approximated to 0V, instead of generating the first and the second amplified modulation signals MA 1 and MA 2 . Further details are described later referring to FIG. 3 .

The audio signal amplifying device according to the exemplary embodiment may further include a voltage control unit (not shown). The voltage control unit checks whether the maximum voltage value of the audio signal A 0 is equal to or lower than the critical value. Then, in the case where the maximum voltage value of the audio signal A 0 is equal to or lower than the critical value, the voltage control unit controls the amplified modulation signal generation unit 130 to output two voltages approximated to 0V, instead of the first and the second amplified modulation signals MA 1 and MA 2 .

The first output unit 142 outputs the first amplified modulation signal MA 1 or a second power supply voltage P 2 , as a third amplified modulation signal MA 3 , according to a logic state of a third modulation signal M 3 . Herein, the third modulation signal M 3 is a result of comparing the third carrier wave C 3 with the audio signal A 0 .

For instance, in the case where the logic state of the third modulation signal M 3 is a low level state, the first amplified modulation signal MA 1 may be output. In the case where the logic state of the third modulation signal M 3 is a high level state, the second power supply voltage P 2 may be output. On the other hand, in the case where the logic state of the third modulation signal M 3 is a low level state, the first output unit 142 outputs the first amplified modulation signal MA 1 . Thus, the third amplified modulation signal MA 3 has a voltage value of the first power supply voltage P 1 or 0V. In the case where the logic state of the third modulation signal M 3 is the high level state, the first output unit 142 outputs the second power supply voltage P 2 , and thus the third amplified modulation signal MA 3 has a voltage value of the second power supply voltage P 2 .

In summary, the third amplified modulation signal MA 3 has a voltage value of 0V, the first power supply voltage P 1 , or the second power supply voltage P 2 , according to the logic state of the third modulation signal M 3 . At this time, the second power supply voltage P 2 may have the same absolute voltage value as the first power supply voltage P 1 with a different sign.

Meanwhile, the exemplary embodiment is not limited to the above case. That is, the first amplified modulation signal MA 1 may be output in the case where the logic state of the third modulation signal M 3 is a high level state, and the second power supply voltage P 2 may be outputted in the case where the logic state of the third modulation signal M 3 is a low level state.

The second output unit 144 outputs the second amplified modulation signal MA 2 or the second power supply voltage P 2 , as a fourth amplified modulation signal MA 4 , according to a logic state of a fourth modulation signal M 4 . Herein, the fourth modulation signal M 4 is a result of comparing the fourth carrier wave C 4 with the audio signal A 0 .

For instance, in the case where the logic state of the fourth modulation signal M 4 is a low level state, the second amplified modulation signal MA 2 may be output. In the case where the logic state of the fourth modulation signal M 4 is a high level state, the second power supply voltage P 2 may be output. That is, the fourth amplified modulation signal MA 4 has a voltage value of 0V, the first power supply voltage P 1 , or the second power supply voltage P 2 , according to the logic state of the fourth modulation signal M 4 .

Meanwhile, the exemplary embodiment invention is not limited to the above case. That is, the second amplified modulation signal MA 4 may be output in the case where the logic state of the fourth modulation signal M 4 is a high level state, and the second power supply voltage P 2 may be output in the case where the logic state of the fourth modulation signal M 4 is a low level state. In the exemplary embodiment, the first to the fourth modulation signals M 1 to M 4 and the first to the fourth amplified modulation signals MA 1 to MA 4 may be Pulse Width Modulation (PWM) signals.

The final output unit 150 synthesizes the output value (MA 1 or P 2 ) of the first output unit 142 and the output value (MA 2 or P 2 ) of the second output unit 144 , i.e., the third amplified modulation signal MA 3 and the fourth amplified modulation signal MA 4 , and outputs a final output signal F 0 .

At this time, since each of the third and the fourth amplified modulation signals MA 3 and MA 4 has a voltage value of 0V, the first power supply voltage P 1 , or the second power supply voltage P 2 , the final output signal F 0 output from the final output unit 150 may have a voltage value of 0V, the first power supply voltage P 1 , the second power supply voltage P 2 , double of the first power supply voltage P 1 , or double of the second power supply voltage P 2 . Also, a form of the final output signal F 0 becomes similar to that of the audio signal A 0 input to the audio signal amplifying device 100 . That is, the final output signal F 0 becomes an amplified version of the audio signal A 0 received through the receiving unit 110 .

In another exemplary embodiment, the final output unit 150 may receive the third and the fourth amplified modulation signals MA 3 and MA 4 through a positive (+) input unit and a negative (−) input unit of the final output unit 150 , respectively. Accordingly, the final output unit 150 multiplies the fourth amplified modulation signal MA 4 by a negative sign, and synthesizes the fourth amplified modulation signal MA 4 multiplied by a negative sign and the third amplified modulation signal MA 3 , and then outputs the final output signal F 0 .

Meanwhile, for outputting the final output signal F 0 amplified to the same voltage value, the first power supply voltage P 1 and the second power supply voltage P 2 , supplied to the audio signal amplifying device 100 according to the exemplary embodiment, are reduced to half the value of those signals of the conventional audio signal amplifying device. That is, the conventional audio signal amplifying device outputs the final output signal F 0 , which is amplified to the first power supply voltage P 1 or the second power supply voltage P 2 , when the conventional audio signal amplifying device is supplied with the first power supply voltage P 1 and the second power supply voltage P 2 . However, the audio signal amplifying device 100 according to the exemplary embodiment is capable of outputting the final output signal F 0 , which is amplified to double of the first power supply voltage P 1 or double of the second power supply voltage P 2 , when the audio signal amplifying device 100 is supplied with the first power supply voltage P 1 and the second power supply voltage P 2 .

FIG. 2 is a diagram illustrating an audio signal amplifying device according to another exemplary embodiment.

Referring to FIG. 2 , the audio signal amplifying device 200 A according to this exemplary embodiment includes first to third phase shifters 212 , 214 and 216 ; an amplified modulation signal generation unit 220 ; first and second output units 232 and 234 ; first and second demodulation filters 242 and 244 ; and a final output unit 250 . In the exemplary embodiment of FIG. 2 , corresponding units of the receiving unit 110 and the carrier wave generation unit 120 of FIG. 1 are omitted. However, the audio signal amplifying device 200 A according to the exemplary embodiment of FIG. 2 may further include the corresponding units of the receiving unit 110 and the carrier wave generation unit 120 of FIG. 1 .

The first phase shifter 212 generates a second carrier wave C 2 by shifting a phase of a first carrier wave C 1 as much as 180 degrees when the first phase shifter 212 receives the first carrier wave C 1 .

The second phase shifter 214 generates a third carrier wave C 3 by shifting the phase of the first carrier wave C 1 as much as 90 degrees when the second phase shifter 214 receives the first carrier wave C 1 .

The third phase shifter 216 generates a fourth carrier wave C 4 by shifting the phase of the third carrier wave C 3 as much as 180 degrees when the third phase shifter 216 receives the third carrier wave C 3 .

In another exemplary embodiment, a single unit including all of the first to the third phase shifters 212 to 216 may generate the first carrier wave C 1 , and may generate the second to the fourth carrier waves C 2 to C 4 using the first to the third phase shifters 212 to 216 . Meanwhile, the phases of the first to the fourth carrier waves C 1 to C 4 are not limited to the above-described example.

The amplified modulation signal generation unit 220 generates a first amplified modulation signal MA 1 and a second amplified modulation signal MA 2 by amplifying a first modulation signal M 1 and a second modulation signal M 2 , respectively, based on a value of a first power supply voltage +½ PVDD. Herein, the first and the second modulation signals M 1 and M 2 are respective results of comparing the first and the second carrier waves C 1 and C 2 with an audio signal A 0 .

In detail, a first comparator 222 a generates the first modulation signal M 1 by comparing the first carrier wave C 1 with the audio signal A 0 . A first output buffer 224 a outputs the first modulation signal M 1 to a first P-type Metal Oxide Semiconductor (PMOS) transistor 226 a and a first N-type Metal Oxide Semiconductor (NMOS) transistor 228 a.

Accordingly, the first PMOS transistor 226 a is turned on when the first modulation signal M 1 has a low level state, and thus the first PMOS transistor 226 a outputs the first power supply voltage +½ PVDD. The first NMOS transistor 228 a is turned on when the first modulation signal M 1 has a high level state, and thus the first NMOS transistor 228 a outputs a ground voltage GND. In this manner, the first PMOS transistor 226 a and the first NMOS transistor 228 a output the first amplified modulation signal MA 1 through a first middle output terminal Vout_a. This first amplified modulation signal MA 1 is supplied to the first output unit 232 .

A second comparator 222 b generates the second modulation signal M 2 by comparing the second carrier wave C 2 with the audio signal A 0 . A second output buffer 224 b outputs the second modulation signal M 2 to a second PMOS transistor 226 b and a second NMOS transistor 228 b.

Accordingly, the second PMOS transistor 226 b is turned on when the second modulation signal M 2 has a low level state, and thus the second PMOS transistor 226 b outputs the first power supply voltage +½ PVDD. The second NMOS transistor 228 b is turned on when the second modulation signal M 2 has a high level state, and thus the second NMOS transistor 228 b outputs the ground voltage GND. In this manner, the second PMOS transistor 226 b and the second NMOS transistor 228 b output the second amplified modulation signal MA 2 through a second middle output terminal Vout_b. This second amplified modulation signal MA 2 is supplied to the second output unit 234 .

The first output unit 232 outputs the first amplified modulation signal MA 1 or a second power supply voltage P 2 , as a third amplified modulation signal MA 3 , according to a logic state of a third modulation signal M 3 . Herein, the third modulation signal M 3 is a result of comparing the third carrier wave C 3 with the audio signal A 0 .

In detail, a third comparator 232 a generates the third modulation signal M 3 by comparing the third carrier wave C 3 with the audio signal A 0 . A third output buffer 232 b outputs the third modulation signal M 3 to a third PMOS transistor 232 c and a third NMOS transistor 232 d.

Accordingly, the third PMOS transistor 232 c is turned on when the third modulation signal M 3 has a low level state, and thus the third PMOS transistor 232 c outputs the first amplified modulation signal MA 1 input to the first output unit 232 through the first middle output terminal Vout_a of the amplified modulation signal generation unit 220 . The third NMOS transistor 232 d is turned on when the third modulation signal M 3 has a high level state, and thus the third NMOS transistor 232 d outputs the second power supply voltage, i.e., −½ PVDD. In this manner, the third PMOS transistor 232 c and the third NMOS transistor 232 d output the third amplified modulation signal MA 3 through a third middle output terminal Vout_c.

As a result, the third amplified modulation signal MA 3 output by the first output unit 232 has a voltage value of 0V, +½ PVDD, or −½ PVDD, according to the logic state of the third modulation signal M 3 .

The second output unit 234 outputs the second amplified modulation signal MA 2 or the second power supply voltage P 2 , as a fourth amplified modulation signal MA 4 , according to a logic state of a fourth modulation signal M 4 . Herein, the fourth modulation signal M 4 is a result of comparing the fourth carrier wave C 4 with the audio signal A 0 .

In detail, a fourth comparator 234 a generates the fourth modulation signal M 4 by comparing the fourth carrier wave C 4 with the audio signal A 0 . A fourth output buffer 234 b outputs the fourth modulation signal M 4 to a fourth PMOS transistor 234 c and a fourth NMOS transistor 234 d.

Accordingly, the fourth PMOS transistor 234 c is turned on when the fourth modulation signal M 4 has a low level state, and thus the fourth PMOS transistor 234 c outputs the second amplified modulation signal MA 2 input to the second output unit 234 through the second middle output terminal Vout_b of the amplified modulation signal generation unit 220 . The fourth NMOS transistor 234 d is turned on when the fourth modulation signal M 4 has a high level state, and thus the fourth NMOS transistor 234 d outputs the second power supply voltage −½ PVDD. In this manner, the fourth PMOS transistor 234 c and the fourth NMOS transistor 234 d output the fourth amplified modulation signal MA 4 through a fourth middle output terminal Vout_d.

As a result, the fourth amplified modulation signal MA 4 output by the second output unit 234 has a voltage value of 0V, +½ PVDD, or −½ PVDD, according to the logic state of the fourth modulation signal M 4 .

The first demodulation filter 242 performs a demodulation operation for eliminating a carrier wave element from the third amplified modulation signal MA 3 .

The second demodulation filter 244 performs the demodulation operation for eliminating a carrier wave element from the fourth amplified modulation signal MA 4 .

At this time, the first and the second demodulation filters 242 and 244 may include an inductor and a capacitor. As the voltage and current of the third and the fourth amplified modulation signals MA 3 and MA 4 respectively inputted to the first and the second demodulation filters 242 and 244 become smaller, the size of the inductor of the first and the second demodulation filters 242 and 244 becomes smaller.

In the audio signal amplifying device 200 A according to the exemplary embodiment, the values of the voltage and current of the third and the fourth amplified modulation signals MA 3 and MA 4 input to the first and the second demodulation filters 242 and 244 are smaller than those of signals input to demodulation filters of the conventional audio signal amplifying device with the conventional class D modulation method. Therefore, in comparison with the conventional technology, the sizes of the first and the second demodulation filters 242 and 244 may be decreased. Also, if the values of the voltage and current of the third and the fourth amplified modulation signals MA 3 and MA 4 input to the first and the second demodulation filters 242 and 244 become smaller, the power consumption of the audio signal amplifying device according to the exemplary embodiment is reduced in comparison with the conventional technology.

The difference between the signals input to the demodulation filters of the conventional audio signal amplifying device with the class D modulation method and the third and the fourth amplified modulation signals input to the first and the second demodulation filters of the audio signal amplifying device 200 A according to the exemplary embodiment is described later referring to FIGS. 4A and 4B .

The final output unit 250 outputs a final output signal F 0 by synthesizing the third and the fourth amplified modulation signals MA 3 and MA 4 , to which the demodulation operation has been performed by the first and the second demodulation filters 242 and 244 .

As illustrated in FIG. 2 , since the final output signal F 0 is outputted by amplifying the audio signal A 0 inputted to the audio signal amplifying device, the final output signal F 0 has the same sinusoidal form as the audio signal A 0 .

Meanwhile, as described above, the final output unit 250 may receive the third and the fourth amplified modulation signals MA 3 and MA 4 through a positive (+) input unit and a negative (−) input unit of the final output unit 250 , respectively.

FIG. 3 is a diagram illustrating an audio signal amplifying device according to another exemplary embodiment.

The audio signal amplifying device 200 B of FIG. 3 , like that of the audio signal amplifying device 200 A FIG. 2 , includes first to third phase shifters 212 , 214 and 216 ; an amplified modulation signal generation unit 220 ; first and second output units 232 and 234 ; first and second demodulation filters 242 and 244 ; and a final output unit 250 .

However, in the audio signal amplifying device 200 B of FIG. 3 , the maximum voltage value of the audio signal A 0 is much smaller than that of the audio signal amplifying device 200 A of FIG. 2 . Accordingly, the amplified modulation signal generation unit 220 outputs the ground voltage GND through a first middle output terminal Vout_a and a second middle output terminal Vout_b.

An operation of the amplified modulation signal generation unit 220 is described in detail as follows.

If the maximum voltage value of the input audio signal A 0 is equal to or lower than a critical value, a first comparator 222 a outputs a signal of a high level. A first output buffer 224 a outputs the high level signal to a first PMOS transistor 226 a and a first NMOS transistor 228 a.

Accordingly, the first PMOS transistor 226 a is turned off and the first NMOS transistor 228 a is turned on so that the first PMOS transistor 226 a and the first NMOS transistor 228 a output the ground voltage GND. Thus, the ground voltage GND is outputted through the first middle output terminal Vout_a.

Also, if the maximum voltage value of the inputted audio signal A 0 is equal to or lower than the critical value, a second comparator 222 b outputs a signal of a high level. A second output buffer 224 b outputs the high level signal to a second PMOS transistor 226 b and a second NMOS transistor 228 b.

Accordingly, the second PMOS transistor 226 b is turned off and the second NMOS transistor 228 b is turned on so that the second PMOS transistor 226 b and the second NMOS transistor 228 b output the ground voltage GND. Thus, the ground voltage GND is outputted through the second middle output terminal Vout_b.

The first output unit 232 outputs the ground voltage GND or the second power supply voltage P 2 , as a third amplified modulation signal MA 3 , according to a logic state of the third modulation signal M 3 . Herein, the third modulation signal M 3 is a result of comparing the third carrier wave C 3 with the audio signal A 0 .

Accordingly, the third amplified modulation signal MA 3 output by the first output unit 232 has a voltage value of 0V or −½ PVDD, according to the logic state of the third modulation signal M 3 .

The second output unit 234 outputs the ground voltage GND or the second power supply voltage P 2 , as a fourth amplified modulation signal MA 4 , according to a logic state of the fourth modulation signal M 4 . Herein, the fourth modulation signal M 4 is a result of comparing the fourth carrier wave C 4 with the audio signal A 0 .

Accordingly, the fourth amplified modulation signal MA 4 output by the second output unit 234 has a voltage value of 0V or −½ PVDD, according to the logic state of the fourth modulation signal M 4 .

The final output unit 250 outputs a final output signal F 0 by synthesizing the third and the fourth amplified modulation signals MA 3 and MA 4 , to which the demodulation operation has been performed by the first and the second demodulation filters 242 and 244 .

In this manner, according to the exemplary embodiment of FIG. 3 , in the case where the voltage value of the audio signal A 0 input to the audio signal amplifying device 200 B is equal to or smaller than the critical value, the final output signal F 0 outputted from the final output unit 250 does not greatly switch from −PVDD to +PVDD, but switches in a range from −½ PVDD to +½ PVDD. Therefore, in the case where the voltage value of the input audio signal A 0 is small, the switching voltage height for the audio signal A 0 is lowered. As a result, the power consumption of the audio signal amplifying device is reduced.

Except for the above explanations, the units illustrated in FIG. 3 perform the same operations as the units illustrated in FIG. 2 . Therefore, detailed explanations are omitted.

Referring to FIGS. 4A and 4B , the difference between the voltage values of the signals input to the demodulation filters of the conventional audio signal amplifying device and the third and the fourth amplified modulation signals MA 3 and MA 4 input to the demodulations filters of the audio signal amplifying device according to the exemplary embodiment is described as follows.

FIG. 4A is a diagram for explaining the voltage values of the signals inputted to the demodulation filters of the conventional audio signal amplifying device.

In FIG. 4A , a switching voltage value of a first synthesized signal 410 a is illustrated at a time domain. Herein, the first synthesized signal 410 a is generated by synthesizing two signals respectively input to two demodulation filters of the conventional audio signal amplifying device. Referring to FIG. 4A , the switching voltage of the first synthesized signal 410 a ranges from −10V to 0V until 100 ms, from 0V to +10V at 100 ms to 150 ms, from −10V to 0V at 150 ms to 200 ms, and from 0V to +10V at 200 ms to 250 ms.

In FIG. 4A , a first sinusoidal signal 420 a overlapped by the first synthesized signal 410 a , illustrated with a solid line, represents a signal that is generated when the carrier wave element is eliminated from the first synthesized signal 410 a . That is, the first sinusoidal signal 420 a is a final output signal obtained by eliminating the carrier wave element from the first synthesized signal 410 a.

FIG. 4B is a diagram for explaining the voltage values of the signals inputted to the demodulation filters of the audio signal amplifying device according to the exemplary embodiment.

In FIG. 4B , a switching voltage value of a second synthesized signal 410 b is illustrated. Herein, the second synthesized signal 410 b is generated by synthesizing the third and the fourth amplified modulation signals MA 3 and MA 4 respectively input to two demodulation filters of the audio signal amplifying device according to the exemplary embodiment. Referring to FIG. 4B , the switching value of the second synthesized signal 410 b is mostly ranged from about −10V to about −5V until 80 ms, from about −5V to about 0V at 90 ms to 100 ms, from about 0V to about +5V at 100 ms to 110 ms, from about +5V to about +10V at 110 ms to 140 ms, from about 0V to about +5V at 140 ms to 150 ms, from about 0V to about −5V at 150 ms to 160 ms, from about −5V to about −10V at 160 ms to 190 ms, from about −5V to about 0V at 190 ms to 200 ms, from about 0V to about +5V at 200 ms to 210 ms, from about +5V to about +10V at 210 ms to 240 ms, and from about 0V to about +5V at 240 ms to 250 ms.

In FIG. 4B , a second sinusoidal signal 420 b overlapped by the second synthesized signal 410 b , illustrated with a solid line, represents a signal which is generated when the carrier wave element is eliminated from the second synthesized signal 410 b . That is, the second sinusoidal signal 420 b is a final output signal obtained by eliminating the carrier wave element from the second synthesized signal 410 b.

Comparing the final output signals of FIGS. 4A and 4B , both of them are sinusoidal signals have voltage levels that range from −10V to 10V.

However, while the first synthesized signal 410 a of FIG. 4A has a voltage level of −10V or +10V during the entire time period, the second synthesized signal 410 b of FIG. 4B not only has a time period of a voltage level of −10V or +10V but also has a time period of a voltage level of −5V or +5V. Therefore, although the maximum voltage value of the second synthesized signal 410 b of FIG. 4B is the same as that of the first synthesized signal 410 a , the average voltage value and average current value of the second synthesized signal 410 b are smaller than those of the first synthesized signal 410 a of FIG. 4A .

Accordingly, the size of the demodulation filters of the audio signal amplifying device according to the exemplary embodiment invention become smaller in comparison to the demodulation filters of the conventional audio signal amplifying device.

FIG. 5 is a flowchart illustrating a method of amplifying the audio signal according to an exemplary embodiment.

In operation 510 , the audio signal A 0 is received.

In operation 520 , the first to the fourth carrier waves C 1 to C 4 , whose phases are different from one another, are generated.

In operation 530 , the first amplified modulation signal MA 1 and the second amplified modulation signal MA 2 are generated by amplifying the first modulation signal M 1 and the second modulation signal M 2 , respectively, based on a voltage value of the first power supply voltage P 1 . Herein, the first and the second modulation signals M 1 and M 2 are respective results of comparing the first and the second carrier waves C 1 and C 2 with the audio signal A 0 .

However, according to another exemplary embodiment, in operation 530 , a control process may be further performed. That is, during the control process, it is checked whether the maximum voltage value of the audio signal A 0 is equal to or lower than the critical value. Then, in the case where the maximum voltage value of the audio signal A 0 is equal to or lower than the critical value, two voltages approximated to 0V are output instead of the first and the second amplified modulation signals MA 1 and MA 2 .

In operation 540 , the first amplified modulation signal MA 1 or the second power supply voltage P 2 is output, as the third amplified modulation signal MA 3 , according to a logic state of the third modulation signal M 3 . Herein, the third modulation signal M 3 is a result of comparing the third carrier wave C 3 with the audio signal A 0 .

In the case where the two voltages approximated to 0V are outputted instead of the first and the second amplified modulation signals MA 1 and MA 2 in operation 530 , the third amplified modulation signal MA 3 has a voltage value approximated to 0V or a voltage value of the second power supply voltage P 2 in operation 540 .

In operation 550 , the second amplified modulation signal MA 2 or the second power supply voltage P 2 is output, as the fourth amplified modulation signal MA 4 , according to a logic state of the fourth modulation signal M 4 . Herein, the fourth modulation signal M 4 is a result of comparing the fourth carrier wave C 4 with the audio signal A 0 .

In the case where the two voltages approximated to 0V are outputted instead of the first and the second amplified modulation signals MA 1 and MA 2 in operation 530 , the fourth amplified modulation signal MA 4 has a voltage value approximated to 0V or a voltage value of the second power supply voltage P 2 in operation 550 .

In operation 560 , the third and the fourth amplified modulation signals MA 3 and MA 4 are synthesized, and then the synthesized signal is outputted.

Meanwhile, the above-described exemplary embodiments may be written as a program to be performed by a computer. By using a computer-readable recording medium, the embodiments may be realized at a general-purpose digital computer including a processor which operates the program.

The computer-readable recording medium includes a magnetic storage medium (e.g., ROM, floppy disk, hard disk and the like) and an optical reading medium (e.g., CD-ROM, DVD and the like).

While the present disclosure has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.