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AR# 43386

FIR Compiler v6.2 - Why is the output of the filters attenuated?


When using FIR Compiler v6.2, the output of the filter is attenuated.

The integer coefficients are scaled to use the maximum dynamic range.

The input and output have the same width.

What can cause this problem?


To calculate the output width, the core combines data width, coefficient width, and bit growth (due to the natural gain of the filter). 

This gives the full precision output width.

If the input width and output width are the same, some rounding mode will be applied to the output, and additional LSBs will be trimmed. 

Normally the value will be attenuated, depending on how many bits are rounded.

To investigate further, you can add another FIR Compiler with full precision output and compare the output values.

AR# 43386
Date Created 07/29/2011
Last Updated 01/05/2015
Status Active
Type General Article
  • ISE Design Suite - 13.2
  • FIR Compiler