Fourth-order single-chip filter

High-order filters are normally designed by using two or more 2nd order sections in series. This means that a 4th-order filter needs at least two opamps. The present filter, however, uses only one opamp, which results in smaller distortion, intermodulation, and so on. Also, there is no internal resonance rise, which typifies combinations of 2nd-order sections. Because of this, the peak input signal may be equal to the peak output of the opamp (but consider the common mode input range).