Patent ID: 7171011

Claim:
An acoustic drive circuit comprising: a first power amplifier having a first input terminal for receiving a first acoustic signal, a second input terminal connected to receive a reference voltage, and a first output terminal, the first power amplifier including a first differential amplifier having a first negative input, a first positive input connected to the second input terminal, and a first output connected to the first output terminal, and also including a first resistor connected between the first input terminal and the first negative input, and a first feedback resistor connected between the first output and the first negative input of the first differential amplifier; a second power amplifier having a third input terminal for receiving a second acoustic signal, a fourth input terminal connected to receive the reference voltage, and a second output terminal, the second power amplifier including a second differential amplifier having a second negative input, a second positive input connected to the fourth input terminal, and a second output connected to the second output terminal, and also including a second resistor connected between the third input terminal and the second negative input, and a second feedback resistor connected between the second output terminal and the second negative input of the second differential amplifier; and a pulse generator having an output terminal for outputting a pulse signal having a frequency higher than frequencies in a speech band and having an average voltage that is equal to about the reference voltage, wherein the first output terminal of the first power amplifier is connected to one end of a first voice coil of a headphone and the second output terminal of the second power amplifier is connected to one end of a second voice coil of the headphone, and the output terminal of the pulse generator is connected to a common terminal between other ends of the first and second voice coils.