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How to caculate FPGA Butterworth Coefficients

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Hi,

 

I am using the National Instruments (FPGA) 'Butterworth Filter' VI, to implement a 2nd order low pass filter.

The input and output signals are Fixed Point numbers with a signed integer word length of minus 4. I have been able to configure the cut-off frequency using the VI's dialog box, but I'd like to make this configurable at run time.The VI has an input called 'Scaled Coefficients', which takes a 3 element array of 32 bit signed integers.I therefore need to determine the value of these coefficients, but the documentation does not include information on how to calculate them.

I have noticed that the Real Time module includes a 'Butterworth Coefficients' VI, which outputs 5 doubles consisting of 3 forward coefficients and 2 reverse.

I am not sure whether i can use these values, or how to scale them to the integers for the FPGA VI?

 

Thanks for your help.

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Accepted by topic author sparkymark567

I have found the VI to calculate the required coefficients under FPGA interface.

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