Amplifier

An amplifier, comprising:

• an input end to which an input signal is applied;
• a low-frequency amplifier circuit that includes
• a first transistor having a gate terminal to which the applied input signal is input, the first transistor being a transistor through which a current depending on the applied input signal flows,
• a load section that is connected to a drain terminal of the first transistor,
• a second transistor of which a gate terminal is connected to the load section, the second transistor being a transistor through which a current depending on a change in a voltage of the drain terminal of the first transistor flows,
• a first resistance to which a source terminal of the first transistor and a drain terminal of the second transistor are connected in common, the first resistance being a resistance through which the current from the first transistor and the current from the second transistor flow, and
• a third transistor that supplies a current approximately equal to the current of the second transistor;
• a high-frequency amplifier circuit that includes
• a constant current circuit,
• a fourth transistor that is connected in series to the input end and the constant current circuit, the fourth transistor being a transistor through which a bias current from the constant current circuit flows,
• a first capacitor that is connected in parallel to the constant current circuit and causes an alternating current signal from among the input signal to flow into the fourth transistor, and
• a fifth transistor that forms a current mirror circuit with the fourth transistor and supplies a current depending on the current flowing through the fourth transistor;
• and
• an output end from which the current supplied by the third transistor and the current supplied by the fifth transistor are output.