| 摘要 |
A filter circuit having a first variable resistive element determining the time constant of the filter circuit and a band pass filter having a second variable resistive element determining the time constant of the band pass filter. Each variable resistive element is connected to receive a time constant control signal which is obtained through a compensation circuit which receives an output voltage signal from a phase detection circuit for detecting a phase difference between the output signal of the band pass filter and a reference signal. The compensation circuit has a comparison circuit for comparing a first voltage generated by a third variable resistive element and a second voltage generated by a constant trimming resistor to generate the output voltage signal. The resistive values of the first to third variable resistive elements vary in proportion to each other, thereby controlling the time constant of the filter circuit to be free from the influence of the variance of the resistive element of the filter circuit.
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