A Multi-Rate Filter for Broadband Radiotelescopes

We have investigated the implementation of various structures based on the Cascaded Integrator Comb (CIC) filter to replace the decimation filter in the first stage, 32-time demultiplexed input digital filter of the large Correlator System of the ALMA (Atacama Large Millimeter Array) interferometer project. The main goal of this study is to reduce the power dissipation in the 2-stage, 32-time demultiplexed ALMA digital filter implemeneted in large FPGA's by optimizing the used number of logic elements available in these chips. Different modified CIC filter implementations are presented and compared in terms of complexity and power performances. We conclude that a CIC filter with a Quarter-band filter significantly improve the overall power dissipation and thus the ALMA filter efficiency.