| 摘要 |
PROBLEM TO BE SOLVED: To provide a filter circuit for stabilizing gain ripple or group delay ripple by making a unity gain frequency of operational amplifiers constant so as to make a Q value constant. SOLUTION: The filter circuit utilizing operational amplifiers the cut-off frequency of which is made constant by varying the resistance of resistive elements or the capacitance of capacitive elements is provided, which includes: a unity gain angular frequency stabilizing circuit that has a circuit for copying an input differential stage of the operational amplifiers, a voltage source connected to an input of the copy of the differential stage, a current generating source for generating a current on the basis of control for making the cut-off destination constant, wherein an output of the current generating source is connected to an output of the copy of the input differential stage to adjust the output of the copy of the differential stage, and a feedback is inputted to a gate of a transistor for generating a bias current of the copy of the differential stage; and a means for inputting an output of the unity gain angular frequency stabilizing circuit to the gate of the transistor generating the bias current of the input differential stage by each operational amplifier for configuring the filter circuit. COPYRIGHT: (C)2007,JPO&INPIT
|
