FPGA Central

hi! All,
i would like some info on implementing cascade form IIR
filters...does matlab support it???...as far as i can understand
butter,cheby1,cheby2,bessel,ellip generate coefficients in the direct
form...how do i implement the cascade form...

TIA
bngguy

bngguy wrote:
> hi! All,
> i would like some info on implementing cascade form IIR
> filters...does matlab support it???...as far as i can understand
> butter,cheby1,cheby2,bessel,ellip generate coefficients in the direct
> form...how do i implement the cascade form...
>
> TIA
> bngguy

I don't know if Matlab supports it, but cascading filters is relatively
easy. Here's the process I use:

1. Factor your numerator and denominator polynomials
2. Combine all your complex pairs into 2nd-order polynomials
3. Match zeros up to their closest denominators (I don't know the
"best" way to do this, use your intuition).
4. Build as many 1st- and 2nd- order polynomials you need
5. Check your gains from the input to the states, to verify
that nothing will overflow.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Matlab generally refers to this as second order sections or SOS for short.
There are several functions in the SP toolbox that convert to/from the SOS form
including TF2SOS.

"Tim Wescott" <[email protected]> wrote in message
news:[email protected]..
> bngguy wrote:
> > hi! All,
> > i would like some info on implementing cascade form IIR
> > filters...does matlab support it???...as far as i can understand
> > butter,cheby1,cheby2,bessel,ellip generate coefficients in the direct
> > form...how do i implement the cascade form...
> >
> > TIA
> > bngguy
>
> I don't know if Matlab supports it, but cascading filters is relatively
> easy. Here's the process I use:
>
> 1. Factor your numerator and denominator polynomials
> 2. Combine all your complex pairs into 2nd-order polynomials
> 3. Match zeros up to their closest denominators (I don't know the
> "best" way to do this, use your intuition).
> 4. Build as many 1st- and 2nd- order polynomials you need
> 5. Check your gains from the input to the states, to verify
> that nothing will overflow.

bngguy wrote:

> hi! All,
> i would like some info on implementing cascade form IIR
> filters...does matlab support it???...as far as i can understand
> butter,cheby1,cheby2,bessel,ellip generate coefficients in the direct
> form...how do i implement the cascade form...
>
> TIA
> bngguy

"Cascade" refers to a chain of second-order sections. Sure, Matlab does
that.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Hello,

Yes, Mathlab supports it. Also, ONEoverT will implement cascade form IIR filter
very easily as well.

Bob Carter

[email protected] (bngguy) wrote in message news:<[email protected] com>...
> hi! All,
> i would like some info on implementing cascade form IIR
> filters...does matlab support it???...as far as i can understand
> butter,cheby1,cheby2,bessel,ellip generate coefficients in the direct
> form...how do i implement the cascade form...
>
> TIA
> bngguy