Bias circuit and amplifier using the same

A bias circuit, comprising:

• a first current source which generates and outputs a first current;
• a second current source which generates and outputs a second current having a temperature-to-output current characteristic that an output current characteristic increases or decreases with a change in temperature to intersect with that of the first current;
• a first field effect transistor which converts the first current inputted from the first current source into a drain terminal thereof to a first voltage, and outputs the first voltage;
• a second field effect transistor which converts the second current inputted from the second current source into a drain terminal thereof to a second voltage, and outputs the second voltage;
• a differential amplifier which has a positive input terminal and a negative input terminal, compares the first voltage inputted from the first field effect transistor into the negative input terminal and the second voltage inputted from the second field effect transistor into the positive input terminal, and outputs a third voltage that is a difference according to a result of the comparison;
• a third field effect transistor which permits a third current to flow from a direct-current power supply according to a value of the third voltage inputted into a gate terminal thereof;
• a fourth field effect transistor which converts the second voltage inputted from the second field effect transistor into a gate terminal thereof to a current for bias;
• and
• a current combining unit which connects an output terminal of the second current source and the drain terminal of the second field effect transistor to combine the second current and the third current and input a resulting current into the drain terminal of the second field effect transistor.