Patent ID: 7420413

Claim:
An amplifier circuit of a BTL system, comprising: a first operational amplifier circuit which outputs an output signal having a same phase as an input signal input to a signal input terminal; a second operational amplifier circuit which outputs an output signal having an opposite phase to the input signal; a voltage dividing circuit which generates a midpoint voltage of the input signal; a first resistance element which is connected between an output terminal of the first operational amplifier circuit and a negative phase input terminal of the first operational amplifier circuit; a second resistance element and a third resistance element which are connected in series between the negative phase input terminal of the first operational amplifier circuit and a negative phase input terminal of the second operational amplifier circuit; a fourth resistance element which is connected between an output terminal of the second operational amplifier circuit and the negative phase input terminal of the second operational amplifier circuit; and an impedance conversion circuit which is connected between a midpoint voltage node of the voltage dividing circuit and a series-connection node of the second resistance element and the third resistance element, the impedance conversion circuit being connected directly to the series-connection node of the second resistance element and the third resistance element.