PROBLEM TO BE SOLVED: To provide a monitoring device capable of monitoring minute change in state of a monitoring target using a capacitance variation detection circuit that offers an extended range of detectable capacitance variation.SOLUTION: A capacitance variation detection circuit 20 comprises a Colpitts oscillator circuit 14, a human body detector section 8, a variable resistance circuit 9, an amplitude detection circuit 16, and a signal amplifier circuit 12. The amplitude detection circuit 16 changes resistance R3 of the variable resistance circuit 9 in accordance with an amplitude of an output voltage Vd of an amplifier circuit 4. When the Colpitts oscillator circuit 14 stops oscillating in response to a capacitance change of the human body detector section 8, the amplitude detection circuit 16 changes the resistance of the variable resistance circuit 9 such that the oscillation is resumed. A filter circuit 29 extracts a signal in a frequency band corresponding to motion of a monitoring target from a signal Vo representing an amplitude of the output of the amplifier circuit 4.SELECTED DRAWING: Figure 1COPYRIGHT: (C)2018,JPO&INPIT【課題】検出可能な静電容量の変化の範囲が拡大された静電容量変化検出回路を使用し、監視対象の細かな状態変化を監視できる監視装置を提供する。【解決手段】静電容量変化検出回路20は、コルピッツ発振回路14と、人体検知部8と、可変抵抗回路9と、振幅検出回路16と、信号増幅回路12とを含む。振幅検出回路16は、増幅回路4の出力電圧Vdの振幅に応じて可変抵抗回路9の抵抗値R3を変化させる。振幅検出回路16は、人体検知部8の静電容量変化に応じてコルピッツ発振回路14の発振が停止したときに、発振が再開するように可変抵抗回路9の抵抗値を変化させる。フィルタ回路29は、増幅回路4の出力の振幅の変化を示す信号Voから監視対象の動作に対応する帯域の信号を抽出する。【選択図】図1
