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AR# 62425

Vivado2014.2 FIR Compiler 7.1- Fractional Rate FIR Compiler 7.1 does not accept symmetric co-efficients


FIR Compiler 7.1 Sysgen block sets do not allow symmetric co-efficients, while IP catalog has removed the option completely.
What is the reason behind this restriction in the core user guide?

Steps To Reproduce:

Filter Type: Interpolation
Rate Change Type: Fixed_Fractional
Interpolation Rate Value: 5
Decimation Rate Value: 4

Quantization : Integer_Coefficients
Coefficeint_Width: 18
Coefficient structure : Select Symmetric. Note that the setting will be returned back to Non_Symmetric


Coefficient symmetry has never been supported for fractional rate filters.

This is noted in the "Notable Limitations" section of the Product Guide/Datasheet.

The GUI has always restricted the Coefficient Structure parameter to "Non Symmetric" and "Inferred" for fractional rate filters in both Vivado and Coregen, where "Inferred" will only result in a non symmetric implementation.

A coefficient vector with symmetric characteristics can still be supplied to the core but the symmetry is not exploited.

The Product Guide/Datasheet section "Polyphase Interpolator Exploiting Symmetric Pairs" explains what is required to support symmetry for an integer rate filter.

This cannot be extended for fractional rate change as it will not use every polyphase with every input sample provided.

Fractional decimation could potentially support symmetry but it has not been of high enough priority for it to be added to the core.
AR# 62425
Date Created 10/09/2014
Last Updated 10/13/2014
Status Active
Type General Article
  • FIR Compiler