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Hello,

Has anyone compared FPGA implementations of full-rate digital FIR = filters based on the use of Multiplier Blocks vs. traditional FIRs with = constant coefficient multipliers? By full rate, I mean: one output = result per clock cycle and no interpolation or decimation.

For anyone not familiar, a multiplier block is a network of shifters and = adders that performs multiplications by several coefficients efficiently = by exploiting common sub-expressions. The multiplier block can be = exploited in FIR filters by transposing the standard filter so that the = products of all the coefficients with the current input-sample are = required simultaneously.

Also, by representing the coefficients in the Canonical-Signed-Digit = number system (a small number of +1 and -1's) along common = sub-expression sharing the multiplier block can get even smaller.

For example, the multiplier block for a 100 tap FIR filter (fp=3D0.10 = and fs=3D0.12) can be realized with only 61 adds (zero explicit = multiplications). See filter example #4 in "FIR Filter Synthesis = Algorithms for Minimizing the Delay and the Number of Adders," =

If the adder depth is constrained to a maximum of four, then the = authors' algorithm can do the multiplier block in 69 additions.

It would seem that this approach would be very efficient in a target = such as the Xilinx Spartan-IIE (with no dedicated multipliers).

Another question: If we only need one result per K clock periods (K ~=3D =

1000 for audio applications), could a multiplier block approach realized = with, say, bit-serial addition be more efficient than some other = approach such as distributed arithmetic?Comments welcome. Thanks.

-Michael

______________________ Michael E. Spencer, Ph.D. President Signal Processing Solutions, Inc. Web: