Patent ID: 7224226

Claim:
An amplifier comprising: a first terminal to which an alternating signal is inputted; a second terminal connected via an external first resistor to a power supply line; a third terminal to be grounded; a second resistor provided on a signal line in between the second terminal and the third terminal; a differential amplifier, a positive power supply terminal of which being connected to a signal line in between the second terminal and the second resistor, and a negative power supply terminal of which being connected to the third terminal and of an inverting and a non-inverting input terminals of which, the alternating signal being inputted through the first terminal to one input terminal and an output according to the alternating signal being fed back to the other input terminal via a signal line in between the second terminal and the second resistor, and between the one input terminal and the other input terminal, a positive offset voltage higher than a maximum level of the alternating signal at the one input terminal and relative to ground potential being produced in advance; and a third resistor provided between a signal line joining the first terminal and the one input terminal, and a signal line leading to the third terminal to stabilize a direct current component of the alternating signal inputted to the one input terminal to ground potential, wherein a voltage waveform of the alternating signal that has been amplified on the basis of the resistances of the first resistor and the second resistor is produced at the second terminal.