| 摘要 |
PURPOSE: To realize stable operation of the circuit and to obtain high speed responsiveness by making an operation amplifier have a composite amplifier constitution of FET input type operation amplifier and a bipolar input type operation amplifier. CONSTITUTION: The input terminal 10 of the logarithmic amplifier is connected to the negative input terminal 11a of the FET input type operation amplifier 11. In addition, the input terminal 10 is also connected to the negative input terminal 22a of the bipolar input type operation amplifier 22 through a capacitor 16. The output terminal 22c of the bipolar input type operation amplifier 22 is connected to an output terminal 31 at a first stage through a resistor 30. Then, output voltage (positive voltage) generated at the output terminal 22c of the operation amplifier 22 is inputted to an operation amplifier 42 at a second stage and also to a transistor 33. Then, the higher the voltage applied to the emitter 33a of the transistor 33 is, the lower the resistance value between the emitter and a collector and the larger a feedback quantity through a capacitor 32. |
