DSP Blockset

Designing Continuous-Time Classical IIR Filters

The Analog Filter Design block designs and applies continuous-time IIR filters with standard band configurations. All of the analog filter designs let you specify a filter order. The other available parameters depend on the filter type and band configuration, as shown in the table below.

Configuration	Butterworth	Chebyshev I	Chebyshev II	Elliptic
Lowpass	p	p, Rp	s, Rs	p, Rp, Rs
Highpass	p	p, Rp	s, Rs	p, Rp, Rs
Bandpass	p1, p2	p1, p2, Rp	s1, s2, Rs	p1, p2, Rp, Rs
Bandstop	p1, p2	p1, p2, Rp	s1, s2, Rs	p1, p2, Rp, Rs

where:

p	=	passband edge frequency
p1	=	lower passband edge frequency
p2	=	upper cutoff frequency
s	=	stopband edge frequency
s1	=	lower stopband edge frequency
s2	=	upper stopband edge frequency
Rp	=	passband ripple in decibels
Rs	=	stopband attenuation in decibels

For all of the analog filter designs, frequency parameters are in units of radians per second.

The block uses a state-space filter representation, and applies the filter using the State-Space block in the Simulink Continuous library. All of the design methods use Signal Processing Toolbox functions to design the filter:

• The Butterworth design uses the toolbox function butter.
• The Chebyshev type I design uses the toolbox function cheby1.
• The Chebyshev type II design uses the toolbox function cheby2.
• The elliptic design uses the toolbox function ellip.

For more information on the filter design algorithms, see the Signal Processing Toolbox documentation.

Note    The Analog Filter Design block does not work with Simulink's discrete solver, which is enabled when the discrete option is selected in the Solver panel of the Simulation Parameters dialog box. Select one of the continuous solvers (e.g., ode4) instead.

Example: Chebyshev Type II Lowpass Filter

Designing Discrete-Time Special IIR and FIR Filters