Variable gain circuit, high frequency switch, and transistor circuit

A variable gain circuit comprising:

• a first input/output terminal and a second input/output terminal configured to input/output a high frequency signal;
• a transistor having a first signal terminal connected to the first input/output terminal, a second signal terminal connected to the second input/output terminal, and a control terminal;
• a first bias terminal having a first variable voltage, a second bias terminal having a second variable voltage, a third bias terminal having a third variable voltage, and a reference voltage terminal having a fixed voltage, the first, second, and third variable voltages and the fixed voltage being independent of each other;
• a first impedance element connected between the first bias terminal and the first signal terminal;
• a second impedance element connected between the second bias terminal and the second signal terminal;
• a third impedance element connected between the third bias terminal and the control terminal;
• and
• a first switch configured to selectively connect the reference voltage terminal to the control terminal.