Arcetri Astrophysical Observatory

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logosmallarcetri Arcetri Technical Reports 5/2002


Design of a FIR filter using a Virtex2 Xilinx chip 

G. Comoretto

INAF - Arcetri Astrophysical  Observatory

Abstract

In the hybrid correlator proposed for ALMA, a large fraction of the total complexity and cost is represented by the digital filterbank. In this report, an alternative design for the filter unit is presented. This includes a digital baseband converter, to select an arbitrary portion of the input band, and a two-stage filter.  The baseband converter allows the selection of a 62.5 MHz portion of the input band arbitrarily positioned in the 2 GHz IF bandwidth. In this way, it is possilbe to cover it with partially overlapped subbands, allowing a better control of edge effects.  The filter section is composed by a 64-tap coarse FIR filter, used to allow a 1:8 decimation of the input data, and a 128 tap sharp filter, equivalent to a 1024 tap filter operating at the original data rate.  The whole filter can be fit in a Xilinx XC2V1000 FPGA, with a reduction of a factor 4 in total gate usage.

Postscript version of this report.

PDF version of this report.