Patent ID: 8174319

Claim:
An amplifier comprising: a first amplifier comprising an N-type field-effect transistor which receives a reference voltage at a gate, a P-type field-effect transistor connected between a drain of the N-type field-effect transistor and a power supply voltage line, and a constant current source connected between a source of the N-type field-effect transistor and a ground terminal, the first amplifier outputting a voltage from a connecting point of the drain of the N-type field-effect transistor and the P-type field-effect transistor; a second amplifier comprising a resistance, and a P-type field-effect transistor connected in series between the power supply voltage line and the ground terminal, the second amplifier receiving the voltage output from the first amplifier at a gate of the P-type field-effect transistor and outputting a voltage from a connecting point of the P-type field-effect transistor and the resistance; and a switch provided between an output of the first amplifier and the power supply voltage line and comprising an N-type field-effect transistor which receives the reference voltage at a gate.