Digital variable capacitance circuit, resonant circuit, amplification circuit, and transmitter

A radio frequency integrated circuit, comprising,

• an amplification circuit for outputting a radio frequency signal to an antenna;
• a balun including a first terminal, a second terminal, a third terminal, and a fourth terminal;
• and
• a variable capacitance circuit including a fifth terminal and a sixth terminal,
• wherein the first terminal and the second terminal of the balun receive output signals of the amplification circuit,
• wherein the third terminal and the fourth terminal of the balun are connected to the fifth terminal and the sixth terminal of the variable capacitance circuit, respectively, and the fifth terminal is connected to a radio frequency output terminal;
• wherein the variable capacitance circuit comprises a plurality of capacity cells that are connected in parallel between two output terminals,
• wherein one of the capacity cells comprises:
• a first capacitor having one end connected to one of the two output terminals;
• an impedance element that is connected in series with the first capacitor between the two output terminals;
• a transistor that is connected in parallel with the impedance element and is controlled in accordance with a digital control signal;
• a bias voltage supply terminal that is supplied with a bias voltage;
• and
• a control signal that controls the transistor to be turned on or off,
• wherein the bias voltage is supplied to another end of the first capacitor when the transistor is controlled to be turned off.