Patent ID: 7400868

Claim:
An automatic tuning apparatus for filter comprising: an input terminal to which an input signal is inputted; a reference signal generator for outputting a reference signal; a first switching part wherethrough said input signal and said reference signal are inputted and wherefrom either one of them is selectively outputted; a filter having a control terminal wherethrough a control signal for controlling its filter characteristic is inputted, said filter processing the signal outputted from said switching part with said filter characteristic and then outputting the processed signal; an output terminal from which the output signal of said filter is outputted; an amplitude detection part whereto said output signal of said filter is inputted and detects its amplitude; a phase comparator part for detecting the phase difference between the signal before its passing through said filter and the signal after its passing through said filter; and a control part which: in a first mode, controls said first switching part such that said input signal is inputted to said filter and outputted from said output terminal; and in a second mode, controls said first switching part so that said reference signal is inputted to said filter; inputs successively a plural number of control signals to said control terminal of said filter; determines tentatively the value of the control signal based on respective amplitudes detected by said amplitude detection part as coarse tuning step; inputs successively a plural number of control signals in the vicinity of the tentatively determined value to said control terminal; and determines the value of the control signal to be used in said first mode as fine tuning step based on respective phase differences detected by said phase comparator part, wherein, in said second mode, said control part: repeats said coarse tuning step a plurality of times and makes the mode, the median, or the average value obtained from a plural number of repeated results to be the value of the tentatively determined control signal; and/or repeats said fine tuning steps a plurality of times and makes the mode, the median, or the average value obtained from a plural number of repeated results to be the value of said control signal.