How do I get Scaled Coefficients for the FPGA version of the Butterworth Filter

[David_R._Asher]

I am trying to program an FPGA application where I need to be able to change the filter cutoff frequency.  I see that I can make a terminal for the filter coefficients on the Butterworth Filter express VI, but how do I generate those filter coefficents for different cutoff frequencies?  When I use the Butterworth Coefficients VI on the host side it returns small floating point values rather than the large fixed point values that I am seeing on the FPGA side.

Thanks,

David R. Asher

[JLewis · Accepted solution]

Hi David,

In 8.5 or 8.6, there is a shipping example that contains the filter design subVI you need:

examples\R Series\FPGA Fundamentals\Analysis and Control\Filter and DC-RMS\Using Reconfigurable Butterworth Filter - R-series.lvproj

In LabVIEW 2009, there is a new palette under My Computer: FPGA Interface>>Scaling, with a new Butterworth Coefficients VI on it. That will produce the quantized coefficients you need in the format expected by the FPGA Butterworth Filter.

Regards,

Jim