| 摘要 |
This is a filter circuit for keeping a Q value constant and stabilizing the gain ripple and group delay ripple of a filter by keeping the unity gain frequency of an operational amplifier (op-amp). The filter circuit using an op-amp for keeping the cut-off frequency constant by making a resistance or a capacitance value variable comprises a unity gain angular frequency stabilizing circuit provided with a circuit obtained by copying the input differential stage of the operational amplifier, for connecting a current generating source for generating current under the control of keeping the cut-off frequency constant, for adjusting the output of the copy of the input differential stage and feeding back/inputting the adjusted output to the gate of a transistor, and a circuit for inputting the output of the unity gain angular frequency stabilizing circuit to the gate of the transistor for generating the bias current of the input differential stage of each op-amp.
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