Audio signal amplifying device and method

An audio signal amplifying device configured to process a differential input signal and thereby generate a differential output signal, the audio signal amplifying device comprising:

• a signal detection circuit configured to detect a variation in an amplitude of the differential input signal and thereby generate a detection result;
• a voltage supply circuit configured to output one of multiple voltages as a supply voltage according to the detection result, wherein when the detection result indicates that the amplitude of the differential input signal satisfies a first condition, the supply voltage is a first voltage of the multiple voltages, and when the detection result indicates that the amplitude of the input signal satisfies a second condition, the supply voltage is a second voltage of the multiple voltages lower than the first voltage;
• an amplifying circuit configured to receive the supply voltage, then process the differential input signal according to the supply voltage, and then generate the differential output signal;
• and
• a common-mode voltage modulation circuit configured to output one of multiple reference voltages as a common-mode voltage to the amplifying circuit in accordance with the detection result, wherein when the detection result indicates that the amplitude of the differential input signal satisfies the first condition, the common-mode voltage is a first reference voltage of the multiple reference voltages;
• when the detection result indicates that the amplitude of the differential input signal satisfies the second condition, the common-mode voltage is a second reference voltage of the multiple reference voltages;
• and the second reference voltage is lower than the first reference voltage,
• wherein the amplitude of the differential input signal satisfying the first condition is a first amplitude, the amplitude of the differential input signal satisfying the second condition is a second amplitude, and the first amplitude is greater than the second amplitude.