A study of the digital N-path band-pass filter with special purpose applications

The N-path, particularly in the narrow bandpass area, is shown to have distinct advantages over filters realized by the standard low-pass to bandpass transformation. The main advantages are reduced computational requirements, lower coefficient quantization sensitivities and characteristics that make the filter amenable to certain special purpose filter problems. The basic digital N-path bandpass filter accepts N-th order sampled data. Each of the N-th order interwoven sequences is individually filtered by one of N identical low-pass filters. The outputs of the N low-pass filters are combined to attain a bandpass which is a symmetric frequency translation of the low-pass response. The N-path filter was developed from digital N-th order bandpass reconstruction theory. The finite word length effects of the N-path configuration are examined. The filter noise, stability and coefficient quantization sensitivities are shown to depend mainly on the configuration of the low-pass paths.