DIODE DETECTION CIRCUIT

PURPOSE:To obtain a diode detection circuit not causing a change in the detection characteristic depending on an input signal level and ambient temperature by providing an input circuit comprising a detection diode, a resistor, a capacitor and a coil, and providing an operational amplifier and a feedback circuit. CONSTITUTION:When the detection diode D1 performs an ideal detection, the AC component is bypassed by the capacitor C2 and the DC component is fed to the operational amplifier OP. Since a non-inverting input terminal of the amplifier OP is kept at a prescribed potential, the amplifier OP applies feedback operation by using the diode D2 and the resistor R2 so as to bring the level of an inverting input terminal to an equi-potential. In selecting the caharacteristics of both the diodes D1, D2 the same and resistors R1, R2 to have the same resistance, the DC component potential by the diode D2 and the resistor R2 is the same as the DC component potential by the detection diode D1 and the resistor R1. Further, the polarity of the DC potentials is made opposite to each other and led to an output terminal S to obtain an excellent detection characteristic.