| 摘要 |
There is provided a filter device having a function of adjusting the center frequency of a filter. The filter device includes: a filter core unit (102) provided with an adder (109) for outputting an added signal of an input signal and a feedback signal (signal Vf), an AGC circuit for generating an amplification signal in which the added signal is amplified, and a phase shifter (111) for generating the signal Vf by shifting a phase of the amplification signal; an amplitude comparing circuit (101) for comparing the reference amplitude and the amplitude of the signal Vf; a gain control voltage generator (108) for controlling the amplification factor of the AGC circuit (110) based upon the comparison result; a frequency comparing circuit (103) for comparing the reference frequency and the frequency of the signal Vf; a phase shifter control voltage generator (117) for controlling the shift amount of the phase in the phase shifter (111) based upon the comparison result. The gain control voltage generator (108) oscillates the filter core unit (102), while the amplification factor and the shift amount are being controlled. |
