An amplifier comprises a first amplifier circuit which amplifies a first
signal to output an amplified first signal, a circuit which outputs a
second signal corresponding to a difference between the first signal and
the amplified first signal, a second amplifier circuit which amplifies
the second signal to output an amplified second signal, a combine circuit
which outputs an amplified signal by combining the amplified second
signal with the amplified first signal, and a controller which controls a
supply of a power to the first amplifier circuit and the second amplifier
circuit and has a first mode to supply the power to the second amplifier
circuit without supplying the power to the first amplifier circuit.