| 摘要 |
PROBLEM TO BE SOLVED: To provide a low-pass filter circuit whose cut-off frequency can be set with high accuracy, where an attenuation in an attenuation area is not reduced. SOLUTION: This low-pass filter circuit having a component of an amplifier 51 with an output impedance and whose gain is the unity is provided with a compensation purpose filter circuit, consisting of resistors 10, 11 and capacitors 15, 16 that is connected to a stage before and after the low-pass filter circuit via a 2nd amplifier 50. A transfer function of the low-pass filter circuit is a product between a transfer function of a 1st quadratic low-pass filter circuit, and the reciprocal of the transfer function of a 2nd quadratic low-pass filter circuit by taking an output impedance 14 of the amplifier which is the component into account, and the compensation purpose filter circuit is selected to have the transfer function of the 2nd quadratic low-pass filter. Thus, deterioration in the attenuation at an attenuation region is eliminated, and the accuracy of the cut-off frequency to be set can be enhanced.
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