Class-D transconductance amplifier

A circuit for driving an audio loudspeaker, comprising:

• a non-inverting amplifier adapted to receive an audio signal from an audio source at a positive input terminal;
• a feedback network connected between an output of the non-inverting amplifier and a negative input of the non-inverting amplifier;
• a capacitor connected at a first terminal to a first terminal of the audio loudspeaker and a at a second terminal to a second terminal of the audio loudspeaker;
• a power switch adapted to provide drive current to the audio loudspeaker and connected between the output of the non-inverting amplifier and the first terminal of the capacitor;
• a feedback resistor connected between the second terminal of the capacitor and the negative input of the non-inverting, amplifier;
• a sense resistor connected at a first terminal to the second terminal of the capacitor;
• and
• an inductor connected between a second terminal of the sense resistor and ground,
• where the capacitor (C) and the inductor (L) form a passive LC reconstruction filter having at least a portion of the passive LC reconstruction filter situated in a feedback loop of the amplifier and the circuit is adapted to operate in a current feedback mode as a voltage-controlled current source.

A method for driving an audio loudspeaker, comprising:

• operating a class-D audio amplifier in a current feedback mode as a voltage-controlled current source;
• decoupling the audio loudspeaker from the class-D amplifier using a pair of inductors, with a first inductor of the pair of inductors connected in series between a first terminal of a capacitor and a first terminal of the audio loudspeaker and second inductor of the pair of inductors connected in series between a second terminal of the capacitor and a second terminal of the audio loudspeaker;
• reconstructing an audio signal at the audio loudspeaker using a passive class-D reconstruction filter, where at least a portion of the passive class-D reconstruction filter is located within a feedback loop to an input of the class-D audio amplifier;
• and
• driving the audio loudspeaker with the reconstructed audio signal.

A class-D audio amplifier, comprising:

• a power switch adapted to provide drive current to an audio loudspeaker;
• a passive inductor/capacitor (LC) reconstruction filter adapted to situate at least a portion of the passive LC reconstruction filter in a feedback loop to an error amplifier;
• where the class-D audio amplifier operates in a current feedback mode as a voltage-controlled current source;
• and
• a pair of inductors adapted to decouple the power switch and the passive LC reconstruction filter from the audio loudspeaker.