DETECTION CIRCUIT AND GAIN FLUCTUATION DETECTING CIRCUIT

摘要

PROBLEM TO BE SOLVED: To improve detection efficiency and temperature stability without using any complicated circuit or expensive circuit component by adding a temperature compensating circuit to the same detection diode (temperature compensation detection diode) to be biased in the forward direction of DC at all the time by a bias current in the forward direction of the detection diode. SOLUTION: The temperature compensating circuit composed of an operational amplifier IC is added to a diode D2. The inverted input terminal of the operational amplifier IC is connected to the cathode of the diode D2, the non- inverted input terminal is connected to the ground and the output terminal is connected to the anode of the diode D2 and further connected through an inductor L to the anode of a diode D1. Even when the forward voltage value of the diode D2 tries to change because of a temperature change, the anode potentials of the diodes D2 and D1 are oppositely changed and the bias current is maintained at a fixed value. The diode D1 is biased forward and its operating point is set in the area of high detection efficiency.