Method and apparatus to control output power of a digital power amplifier optimized to a headphone and a portable audio player having the same

A digital amplifier usable in a portable audio device, the amplifier comprising:

• a signal processing unit having a variable power supply unit to output a variety of voltages, the signal processing unit receiving an audio signal and amplifying the audio signal based on a DC voltage currently output by the variable power supply unit;
• an impedance measuring unit having a resistive element with a first end connected to the signal processing unit and a second end connected to an output of the portable device and to measure an impedance value of any speaker unit connected to the output of the portable audio device and to output an impedance detection signal;
• and
• a micom unit to receive the impedance detection signal and to control the variable power supply unit to update the DC voltage currently output based on the measured impedance value indicated by the impedance detection signal.

A portable audio device, comprising:

• a signal processing unit which includes a digital amplifier,
• wherein the digital amplifier amplifies a test pulse generation control signal or an audio signal based on a power supply level of a power supply;
• and
• a power supply control unit to vary the power supply level of the power supply based on an impedance of at least one speaker unit connected to the digital amplifier,
• wherein the signal processing unit power amplifies a pulse signal with a predetermined duty cycle and converts the pulse signal into a direct current (DC) voltage in an impedance measuring mode, and
• wherein the signal processing unit power amplifies a pulse signal with a duty cycle corresponding to an instantaneous amplitude of an audio signal in an audio reproduction mode.

A portable audio device, comprising:

• a digital amplifier to amplify an audio signal based on a power supply level of a power supply;
• and
• an apparatus to control an output power of the digital amplifier by varying the power supply level of the power supply based on an impedance of at least one speaker unit connected to the digital amplifier, the apparatus including
• a signal processing unit to power amplify a pulse signal and to convert the pulse signal into a direct current (DC) voltage,
• an impedance measuring unit to connect a resistance device between the signal processing unit and the at least one speaker unit and to detect a voltage value applied to the resistance device and the at least one 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 at least one speaker unit is connected to the portable audio device, to determine the impedance of the at least one speaker unit based on the voltage value detected by the impedance measuring unit, to control a power amplification by providing a voltage level control signal to the signal processing unit according to the determined impedance, and to control an audio level in an audio reproduction mode accordingly.

A portable audio device, comprising:

• a signal processing unit having a first terminal to generate a voltage signal in a headphone impedance measuring mode;
• a second terminal to be connected to an external headphone;
• an impedance measuring unit to selectively connect the first terminal to a first end of a resistive device and the second terminal to a second end of the resistive device to generate one of a first value and a second value according to the voltage signal corresponding to a characteristic of the external headphone;
• and
• a processor unit to control the signal processing unit to generate one of a first audio reproducing signal and a second audio reproducing signal according to the one of the first value and the second value.

A method of controlling output power of a digital audio amplification device, the method comprising:

• if a speaker unit is connected to the digital audio amplification device, setting an impedance measuring mode and generating an arbitrary pulse signal;
• converting the arbitrary pulse signal into a DC voltage;
• applying the DC voltage to a resistance device connected to the speaker unit and detecting a voltage between the resistance device and the speaker unit;
• determining an impedance of the speaker unit based on the detected voltage;
• and
• adjusting a level of audio being reproduced by providing a voltage level control signal to control a switching power level according to the determined impedance of the speaker unit.