Digital amplifier
View Patent ↗A digital amplifier includes a digital PWM generator, a first amplifier circuit, a first low-pass filter, a second amplifier circuit, a second low-pass filter, an attenuator, an error extractor, an adder, and a voltage supply unit. The first amplifier circuit amplifies a digital PWM signal at a second voltage. The first low-pass filter extracts a low-frequency band voltage signal from the amplified digital PWM signal, and outputs the extracted voltage signal to a load. The second amplifier circuit amplifies the generated digital PWM signal at a third voltage. The error extractor extracts an error signal. The adder adds a digital error signal whose feedback gain is adjusted to a digital audio signal. The voltage supply unit generates the third voltage that has a voltage value of a predetermined ratio to a voltage value of the second voltage, and supplies the third voltage to the second amplifier circuit.
1. A digital amplifier comprising:
a digital pulse width modulation (PWM) generator that generates a digital PWM signal corresponding to a digital audio signal by using a first voltage;
a first amplifier circuit that amplifies the digital PWM signal at a second voltage whose absolute value is larger than an absolute value of the first voltage;
a first low-pass filter that extracts low-frequency components, as a first analog voltage signal, from a first amplified digital PWM signal amplified by the first amplifier circuit, and outputs the low-frequency components to a load;
a second amplifier circuit that amplifies the digital PWM signal at a third voltage whose absolute value is smaller than the absolute value of the second voltage;
a second low-pass filter that extracts low-frequency components, as a second analog voltage signal, from a second amplified digital PWM signal amplified by the second amplifier circuit;
a first attenuator that attenuates the first analog voltage signal extracted by the first low-pass filter to generate a first attenuated analog voltage signal;
an error extractor that extracts an error signal based on the second analog voltage signal extracted by the second low-pass filter and the first attenuated analog voltage signal generated by the first attenuator;
a digital error signal generator that generates, from the error signal, a digital error signal whose feedback gain is adjusted, the digital error signal being generated by digitizing the error signal;
an adder that adds the digital error signal to the digital audio signal; and
a voltage supply unit that generates the third voltage that has a voltage value of a predetermined ratio to a voltage value of the second voltage by using the second voltage, and supplies the third voltage to at least the second amplifier circuit.
2. The digital amplifier according to claim 1 , wherein an amplification factor of the second amplifier circuit is equal to a product of an amplification factor of the first amplifier circuit and an attenuation factor of the first attenuator.
3. The digital amplifier according to claim 1 , further comprising:
a third amplifier circuit that amplifies the first voltage;
a second attenuator that attenuates the second voltage;
a second error extractor that extracts, as a differential signal, a difference between the first voltage amplified by the third amplifier circuit and the second voltage attenuated by the second attenuator; and
a digital gain adjuster that increases or decreases a sound volume of the digital audio signal based on the differential signal extracted by the second error extractor.
4. The digital amplifier according to claim 3 , wherein an amplification factor of the second amplifier circuit is equal to a product of an amplification factor of the first amplifier circuit and an attenuation factor of the first attenuator.
5. A digital amplifier comprising:
a digital pulse width modulation (PWM) generator that generates a digital PWM signal corresponding to a digital audio signal by using a first voltage;
a voltage generation circuit that generates a second voltage that has a voltage value of a predetermined ratio to a voltage value of the first voltage by using a third voltage, the second voltage having an absolute value that is larger than an absolute value of the first voltage;
a first amplifier circuit that receives the second voltage and amplifies the digital PWM signal at the second voltage;
a first low-pass filter that extracts low-frequency components, as a first analog voltage signal, from a first amplified digital PWM signal amplified by the first amplifier circuit, and outputs the low-frequency components to a load;
a second amplifier circuit that amplifies the digital PWM signal at the first voltage;
a second low-pass filter that extracts low-frequency components, as a second analog voltage signal, from a second amplified digital PWM signal amplified by the second amplifier circuit;
an attenuator that attenuates the first analog voltage signal extracted by the first low-pass filter to generate a first attenuated analog voltage signal;
an error extractor that extracts an error signal based on the second analog voltage signal extracted by the second low-pass filter and the first attenuated analog voltage signal generated by the attenuator;
a digital error signal generator that generates, from the error signal, a digital error signal whose feedback gain is adjusted, the digital error signal being generated by digitizing the error signal; and
an adder that adds the digital error signal to the digital audio signal.
6. The digital amplifier according to claim 5 , wherein an amplification factor of the second amplifier circuit is equal to a product of an amplification factor of the first amplifier circuit and an attenuation factor of the attenuator.