Discrete-time N-path decimating filters

By combining the advantages of N-path filters together with single-path decimating filters with M-fold reduction of the sampling rate, this paper proposes a new N-path decimating filter building block that has the ability to perform frequency downconversion simultaneous with high selectivity filtering. Besides, while using circuits working at only F, such N-path-decimators provide a rejection of the aliasing frequency components from 0 to MNF/sub s//2 outside the channel passbands. This makes them particularly attractive for radio front-ends in modern communications systems. An example is given using a 5-path system where the output and input sampling frequencies of the decimating pathfilters are, respectively, 6 MHz and 24 MHz, yielding an overall input sampling frequency of 120 MHz and hence extended input baseband from 0 to 60 MHz. A detailed computer-based spectral analysis clearly illustrates the resulting two frequency downconversion channels, one from 24 MHz to 6 MHz and the other from 48 MHz to 12 MHz.