Patent ID: 8014539

Claim:
An apparatus to control an output power of a digital amplifier in a digital audio amplification device, the apparatus comprising: a signal processing unit to power amplify a pulse signal and to convert the pulse signal into a direct current (DC) voltage in an impedance measuring mode and to extract an audio signal from a PWM signal in an audio reproduction mode; an impedance measuring unit to connect a resistance device between the signal processing unit and a speaker unit and to detect a voltage value applied to the resistance device and the speaker unit; and a micom unit to generate a test pulse generation control signal which is modulated into a pulse signal having a predetermined duty cycle in the signal processing unit if the speaker unit is connected to the device, to determine an impedance of the speaker unit based on the voltage value detected by the impedance measuring unit, to control a power amplification of the PWM signal by providing a voltage level control signal to control a switching power level of the signal processing unit according to the determined impedance, and to control an audio level in an audio reproduction mode accordingly.