Impedance detection circuit, impedance detector and method of impedance detection

An impedance detection circuit comprising:

• a first operational amplifier;
• a second operational amplifier of which both input terminals are in an imaginary short status;
• a signal line of which one end is connected to one of the input terminals of the second operational amplifier and the other end is connected to an impedance element;
• a shield that shields electrically at least a part of the signal line;
• a first impedance that is connected between an output terminal of the first operational amplifier and the signal line;
• and
• a signal output terminal that is connected to the output terminal of the first operational amplifier.

An impedance detection method including steps for:

• making both of the input terminals of the second operational amplifier imaginary short;
• connecting one of the input terminals to the signal line and making it into the condition of neither input nor output of current at the input terminal;
• connecting the other input terminal to the shield of at least a part of the signal line;
• and
• detecting a impedance of a impedance element by the current that flows through the first impedance connected to the signal line.