Patent ID: 7298205

Claim:
An amplifier for amplifying differential signal composed of an in-phase signal and an opposite-phase signal, said amplifier comprising: an amplifier circuit, connected to a path from an input terminal to an output terminal, for amplifying the differential signal inputted from the input terminal; a first feedback circuit, which is connected between an input and a feedback terminal of said amplifier circuit and which includes an inductor and a capacitor, for feeding a feedback output of said amplifier circuit back to the input of said amplifier circuit while changing, in one direction, a phase of the signal passing through said first feedback circuit; and a second feedback circuit, which is connected between the input and an output of said amplifier circuit and which includes a circuit in which a resistor and a capacitor are connected in parallel, for feeding the output of said amplifier circuit back to the input of said amplifier circuit while changing, in another direction, a phase of the signal passing through said second feedback circuit, wherein said amplifier circuit includes: an in-phase amplifying section, having an in-phase feedback terminal which is one of phase feedback terminals, for operating based on the in-phase signal of the differential signal; and an opposite-phase amplifying section, having an opposite-phase feedback terminal which is another of the phase feedback terminals, for operating based on the opposite-phase signal of the differential signal, wherein one end of said first feedback circuit is electrically connected to both the in-phase feedback terminal and the opposite-phase feedback terminal, and another end of said first feedback circuit is grounded, wherein said second feedback circuit includes: an in-phase feedback section operating based on the in-phase signal; and an opposite-phase feedback section operating based on the opposite-phase signal; and wherein a phase of a signal in which fundamental waves included in two feedback signals fed back by said first and second feedback circuits are combined is shifted by approximately 180 degrees from a phase of a fundamental wave of the signal inputted from the input terminal.