| 摘要 |
PROBLEM TO BE SOLVED: To provide a tertiary low-pass filter provided with characteristics by one operational amplifier capable of offset correction by performing multiple feedback to an inverted input side through a resistor and a capacitor provided with a specified resistance value and a capacitance value corresponding to a cut-off frequency. SOLUTION: The resistance values of first, second, third and forth resistors are respectively turned toαR, R, R and (1-α)R for the resistance value R corresponding to the cut-off frequency of a circuit and a prescribed rear numberα. The capacitance values of first, second and third capacitors are turned to values to be respectively (1+2α)t0 C/α(2t0 -1)},α(2t0 -1)C/ (1+2α)t0 <2> } and t0 C/α(1-α)} for the capacitance value C corresponding to the cut-off frequency of the circuit and a rear number solution t0 for which the function F(t)=t<3> -2 t<2> +3α(2t-1)/(1+2α) of the real number (t) of 1<(t)<2 at the time of 0.4<α<1 becomes F(t)=0. Thus, this multiple feedback type tertiary low-pass filter provided with the Butter worth characteristics by one operation amplifier capable of the offset correction is realized.
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