FPGA butterworth 3rd order

[charlie87]

Hi,

I want to implement butterworth filter 3rd order in FPGA. It must be possible to change the type (HP,LP,BP,BS) and the parameters (cuttof freq) during FPGA run. I found that there is Butterwort VI in FPGA Palette but it is not possible to change type from my host during the run.

I want to ask what are the other options to implement butterworth 3rd order in FPGA ?

Now my idea is to use Digital filter design toolkit in host to get coef. according the parameters and implement the filters polynom from multiply and add block in FPGA. But I am not sure about this... 

[okubik]

Hi Charlie,

Have you tried "Using Multichannel Butterworth Filter - R-series" example? I think that's exactly what are you looking for.

[charlie87]

Yes I have seen this vi, but it is not what I want. I want to change the type during the run. When I opet this multichannel butterworth vi I cannot set the type (lowpass or highpass) from the host front panel. Only in block properties. Maybe it can be done somehow, but I do not know how. Please explain if it is possible...

[Ardent]

Hi Charlie,

basically you can open the FPGA VI "Using multichannel Butterworth filter (FPGA)". Inside is a express VI called "Butterworth filter" - if you create a SubVI from this express VI (rightclick->convert to subVI), go inside and then rightclick the Butterworth filter and select "Open front panel", you'll see, how the Butterworth is implemented. What more, you can see, where the LP/HP is being changed and bound this to a network shared variable.

Hope this helps.

[charlie87]

I tried what you advised me. Everything works but there is no option to change type of the filter in the sub VI. Please check it if you can and if it is possible please put a picture here or something if it is possible...

[Ardent · Accepted solution]

Hi,

you need to change the "lowpass" constant  at the lowest level to a control. See attached picture - I highlited the constant in question.

Hope this helps

[charlie87]

thanks...now its working. Do you think that it can be possible to change the behaviour of this Butterworth block in multichannel mod ? Multichannel mod does not support 4th order and I would like it

[Ardent]

In that case you will probably have to rewrite the Butterworth filter VI. I would suggest trying to configure a multichannel filter and a 4th order filter, check their block diagrams and afterwards creating your own Butterworth that will support multiple channels and 4th order filter.