A tunable band-pass filter using a complex-arithmetic heterodyne approach

Complex arithmetic allows the separation of the poles and zeros in the top half of the z-plane from the poles and zeros in the bottom half of the z-plane. Heterodyne techniques can then be used to move the poles and zeros in the top half of the plane counter-clockwise and the poles and zeros in the bottom half of the z-plane clockwise. For the case of narrow-band band-pass filters, a significant hardware savings can be obtained by using only the real part of the resulting output.