Filter Design Toolbox™

designopts

Valid input arguments and values for specification object and method

Syntax

options = designopts(d,'designmethod')

Description

options = designopts(d,'designmethod') returns the structure options with the default design parameters used by the design method designmethod, specific to the response you defined for d. Replace designmethod with one of the strings returned by designmethods.

Use help(d,designmethod) to get a description of the design parameters. For example, to see the help for designing a highpass Chebyshev II filter from a specifications object d, enter

help(d,'cheby2')

at the prompt. MATLAB responds with help for Chebyshev II filter designs that use the specification Fst,Fp,Ast,Ap.

DESIGN Design a Chebyshev Type II iir filter.
HD = DESIGN(D, 'cheby2') designs a Chebyshev Type II 
filter specified by the FDESIGN object H.

HD = DESIGN(..., 'FilterStructure', STRUCTURE) returns a 
filter with the structure STRUCTURE.  STRUCTURE is 
'df2sos' by default and can be any of the following.

'df1sos'
'df2sos'
'df1tsos'
'df2tsos'
 
HD = DESIGN(..., 'MatchExactly', MATCH) designs a 
Chebyshev Type II filter and matches the frequency and
magnitude specification for the band MATCH exactly.  
The other band will exceed the specification.  
MATCH can be 'stopband' or 'passband' and is 'passband' 
by default.

Examples

Design a minimum order, lowpass Butterworth filter. Use designmethods to determine the appropriate input arguments. Start by creating a lowpass filter specification object d.

d = fdesign.lowpass;

Because you want information about the input arguments for designing a filter using a design method, use designmethods(d) to get the list of valid methods.

designmethods(d)

Design Methods for class fdesign.lowpass (Fp,Fst,Ap,Ast):


butter
cheby1
cheby2
ellip
equiripple
ifir
kaiserwin
multistage

Pick one method and determine the design options for that method.

options = designopts(d,'butter')

options = 

    FilterStructure: 'df2sos'
       MatchExactly: 'stopband'

In this example, the filter structure is Direct-Form II with second-order sections, and the design seeks to match the desired stopband performance exactly. As you see by reading the help, FilterStructure and MatchExactly are input arguments for designing the Butterworth filter.

Get help for designing a filter from d using the butter design method to see the arguments.

help(d,'butter')

 DESIGN Design a Butterworth IIR filter.
 HD = DESIGN(D, 'butter') designs a Butterworth filter specified by the
 FDESIGN object H.
 
 HD = DESIGN(..., 'FilterStructure', STRUCTURE) returns a filter with the
structure STRUCTURE.  STRUCTURE is 'df2sos' by default and can be any of
the following.

    'df1sos'
    'df2sos'
    'df1tsos'
    'df2tsos'
 
 HD = DESIGN(..., 'MatchExactly', MATCH) designs a Butterworth filter
 and matches the frequency and magnitude specification for the band
 MATCH exactly.  The other band will exceed the specification.  MATCH
 can be 'stopband' or 'passband' and is 'stopband' by default.

See Also

design, designmethods, fdesign

designmethods

dfilt