PROBLEM TO BE SOLVED: To highly precisely detect an impedance of a subject by suppressing the deterioration of a detection precision due to a process fluctuation or the like with a simple circuit constitution.SOLUTION: A waveform information detection section 4 is provided with a reply signal conversion circuit 41 and a digital phase comparison circuit 43, the reply signal conversion circuit 41 converts a reply signal 3S from a reply signal generation section 3 into a comparison object signal 41S consisting of a digital signal indicating a voltage change of the reply signal 3S and outputs it, the digital phase comparison circuit 43 compares the phases of a rectangular-wave digital criterion signal 42S synchronized with a feed signal 2S from a feed signal generation section 2 and the comparison object signal 41S to detect a phase difference between the comparison object signal 41S and the feed signal 2S as waveform information, and generates a detection signal 4S consisting of the digital signal having the pulse width according to the phase difference.COPYRIGHT: (C)2008,JPO&INPIT【課題】簡素な回路構成で、プロセス変動等の要因による検出精度の劣化を抑制でき、被検体のインピーダンスを高精度で検出する。【解決手段】波形情報検出部4に、応答信号変換回路41とデジタル位相比較回路43とを設け、応答信号変換回路41により、応答信号生成部3からの応答信号3Sを当該応答信号3Sの電圧変化を示すデジタル信号からなる被比較信号41Sに変換して出力し、デジタル位相比較回路43により、供給信号生成部2からの供給信号2Sに同期した矩形波のデジタル基準信号42Sと被比較信号41Sとの位相を比較することにより、波形情報として被比較信号41Sと供給信号2Sの位相差を検出し、当該位相差に応じたパルス幅を有するデジタル信号からなる検出信号4Sを生成する。【選択図】 図1
