Digital complex envelope demodulation using nonminimal normal form structures

Through the use of a complex bandpass digital filter with decimated output, the complex envelope of a narrow-band signal can be obtained by multiplying the decimated filter output by a complex exponential sequence. For appropriate choices of decimation ratio, the complex envelope can be obtained directly from the output of the complex filter, with no multiplications by a complex exponential sequence required. In this correspondence we call attention to a new nonminimal recursive structure, derived from the normal form, that can be used for efficient implementation of complex bandass filters with decimated output.