# iirlp2bs

Transform IIR lowpass filter to IIR bandstop filter

## Description

`[`

transforms an IIR lowpass filter to an IIR bandstop filter.`num`

,`den`

,`allpassNum`

,`allpassDen`

] =
iirlp2bs(`b`

,`a`

,`wo`

,`wt`

)

The lowpass filter is specified using the numerator and denominator coefficients
`b`

and `a`

respectively. The function
returns the numerator and denominator coefficients of the transformed bandstop
digital filter. The function also returns the numerator and denominator coefficients
of the allpass mapping filter, `allpassNum`

and
`allpassDen`

respectively.

For more details on the transformation, see IIR Lowpass Filter to IIR Bandstop Filter Transformation.

Frequencies must be normalized to be between 0 and 1, with 1 corresponding to half the sample rate.

## Examples

## Input Arguments

## Output Arguments

## More About

## References

[1] Nowrouzian, B., and A.G.
Constantinides. “Prototype Reference Transfer Function Parameters in the Discrete-Time
Frequency Transformations.” In *Proceedings of the 33rd Midwest
Symposium on Circuits and Systems*, 1078–82. Calgary, Alta., Canada: IEEE,
1991. https://doi.org/10.1109/MWSCAS.1990.140912.

[2] Nowrouzian, B., and L.T.
Bruton. “Closed-Form Solutions for Discrete-Time Elliptic Transfer Functions.” In [1992]
*Proceedings of the 35th Midwest Symposium on Circuits and
Systems* , 784–87. Washington, DC, USA: IEEE, 1992.
https://doi.org/10.1109/MWSCAS.1992.271206.

[3] Constantinides, A.G. “Design
of Bandpass Digital Filters.” *Proceedings of the IEEE*
57, no. 6 (1969): 1229–31. https://doi.org/10.1109/PROC.1969.7216.

[4] Constantinides,
A.G.“Spectral transformations for digital filters.” *
Proceedings of the IEEE*, vol. 117, no. 8: 1585-1590. August
1970.

## Extended Capabilities

## Version History

**Introduced in R2011a**