Patent attributes
A band pass filter includes a first band pass filter constructed of a biquad circuit and having a first center frequency, and a second bandpass filter constructed of a biquad circuit and having a second center frequency different from the first center frequency, and the first band pass filter and the second band pass filter are series connected, in which the first band pass filter and the second band pass filter have center frequency adjusting variable resistors varied at the same time, and a fixed resistor is connected in parallel to the center frequency adjusting variable resistor of one of the first band pass filter and the second band pass filter. As a result, the center frequency and/or the maximum gain can be made variable while the band width is fixed.
