Cascade Linear Phase Recursive Half-Band Filters Implement the Most Efficient Digital Down-Converter "Best of R&D Track"

The digital down converter (DDC) is a fundamental component in modern receivers. Two different architectures, operating on very different principles, have become dominant in modern receiver systems. The first of these is the Edwin Armstrong heterodyne model formed by three processes, a quadrature heterodyne, a low-pass filter, and an M-to-1 down sampler. The second is the band centered polyphase filter in which the three processes are performed in the reverse order, an M-to-1 aliasing down sampler, an Mpath partitioned low-pass filter, and an M-point complex phase-alignment vector. The second option finds great favor in multichannel receivers in which multiple narrowband signals are separated by the single filter coupled to an IFFT that provides the multiple M-point phase alignment vectors. In this paper we present a polyphase filter form of the single channel DDC that offers significant computational advantages over the conventional single channel DDC. This architecture may present the minimum power implementation of a DDC and likely will find great value in battery operated radio receivers.