Filtering transformation in Generalized Quadrature Bandpass Sampling

According to recent research, Generalized Quadrature BandPass Sampling (GQBPS) with FIR filtering is promising to deal with the noise aliasing problem in subsampling systems. However, the interesting band of folded spectra by GQBPS with real FIR filtering is still located at the input carrier frequency. In this paper, inherent FIR filtering in GQBPS with real coefficients is transformed such that the interesting band is shifted to a lower frequency. The main advantage of such transformation is to achieve a frequency downconversion besides sampling and dealing with noise aliasing in GQBPS. As a special case of GQBPS, Uniform Quadrature BandPass Sampling (UQBPS) is also discussed including the filter transformation. Both theoretical analyses and simulations are included. It is verified that the expected noise aliasing improvement of GQBPS or UQBPS does not change with the filter transformation. The whole subsampling system with GQBPS or UQBPS might be simplified by using complex filtering.