| 摘要 |
PROBLEM TO BE SOLVED: To obtain a filter circuit that absorbs dispersion among elements and easily absorbs an environmental change and a secular change so as to compensate the characteristics. SOLUTION: The filter circuit is provided with a changeover device 5 that selects a filter 1 to be a filter of an open circuit or an oscillation circuit of a closed loop, with a phase locked loop(PLL) circuit consisting of a phase comparator 2 that receives an output of the oscillation circuit at one phase input and receives a reference phase at the other phase input when the filter is selected for the oscillation circuit of the closed loop and of a low pass filter 3, and with a sample-hold circuit 4 (S/H) that samples and holds an output of the phase locked loop circuit, whereby the characteristic value of the open circuit is maintained with an output of the sample-hold circuit.
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