Butterworth bandpass gain

Hi, I'm working on butterworth IIR filters, I have my s-plane analogue
prototype and conversions to HP/BS/LP working fine and am able to
calculate gain and scale it correctly, do bilinear and covert to SOS,
no problem.

I'm having trouble finding references about how to calculate an overall
gain for the bandpass case.  Is there any reference or paper that could
shed some light ? Apparently, I need to calculate something other than
the DC gain, the fcutoff gain ? 

any help would be great

thanks!

polar.ninja@gmail.com skrev:
> Hi, I'm working on butterworth IIR filters, I have my s-plane analogue
> prototype and conversions to HP/BS/LP working fine and am able to
> calculate gain and scale it correctly, do bilinear and covert to SOS,
> no problem.
>
> I'm having trouble finding references about how to calculate an overall
> gain for the bandpass case.  Is there any reference or paper that could
> shed some light ? Apparently, I need to calculate something other than
> the DC gain, the fcutoff gain ?

You have to do things in the correct order to get these things to work.
Somewhere along the line you make a LP s-domain prototype. If you
scale this LP prototype filter function such that it has unit gain at
DC,
everythings else comes out correctly once you apply the BLT or
convert to HP, BP or BS filters.

Rune

thanks rune, I got it working!!!

best regards!


Rune Allnor wrote:
> polar.ninja@gmail.com skrev:
> > Hi, I'm working on butterworth IIR filters, I have my s-plane analogue
> > prototype and conversions to HP/BS/LP working fine and am able to
> > calculate gain and scale it correctly, do bilinear and covert to SOS,
> > no problem.
> >
> > I'm having trouble finding references about how to calculate an overall
> > gain for the bandpass case.  Is there any reference or paper that could
> > shed some light ? Apparently, I need to calculate something other than
> > the DC gain, the fcutoff gain ?
>
> You have to do things in the correct order to get these things to work.
> Somewhere along the line you make a LP s-domain prototype. If you
> scale this LP prototype filter function such that it has unit gain at
> DC,
> everythings else comes out correctly once you apply the BLT or
> convert to HP, BP or BS filters.
> 
> Rune