Versatile building blocks for multirate processing of bandpass signals

In this paper we develop a special down-converting bandpass decimator structure which can be used for reducing the sampling rate by a factor two without causing any disturbing aliasing effects for a bandpass signal located originally around quarter of the sampling rate (π/2). Based on this special bandpass filter design and usual halfband lowpass and highpass decimation filters, an efficient stepwise decimation and mixing approach is developed for filtering out and down-converting a narrowband signal located in frequency domain anywhere within a wideband digitized signal. This kind of down-conversion and decimation approach finds applications in communications receivers where the role of DSP-based solutions is becoming more and more important.