Filter Design Toolbox™

cheby1 - Chebyshev Type I filter using specification object

Syntax

hd = design(d,'cheby1')
hd = design(d,'cheby1',designoption,value,designoption,
value,...)

Description

hd = design(d,'cheby1') designs a Chebyshev I IIR digital filter using the specifications supplied in the object d.

hd = design(d,'cheby1',designoption,value,designoption,
value,...) returns a Chebyshev I IIR filter where you specify design options as input arguments.

To determine the available design options, use designopts with the specification object and the design method as input arguments as shown.

designopts(d,'method')

For complete help about using cheby1, refer to the command line help system. For example, to get specific information about using cheby1 with d, the specification object, enter the following at the MATLAB prompt.

help(d,'cheby1')

Examples

These examples use filter specification objects to construct Chebyshev type I filters. In the first example, you use the matchexactly option to ensure the performance of the filter in the passband.

d = fdesign.lowpass
designopts(d,'cheby1')
ans = 

    FilterStructure: 'df2sos'
       MatchExactly: 'passband'

hd = design(d,'cheby1','matchexactly','passband')

d =
 
               Response: 'Lowpass'      
          Specification: 'Fp,Fst,Ap,Ast'
            Description: {4x1 cell}     
    NormalizedFrequency: true           
                  Fpass: 0.45           
                  Fstop: 0.55           
                  Apass: 1              
                  Astop: 60             

hd =
 
         FilterStructure: 'Direct-Form II, Second-Order Sections'
              Arithmetic: 'double'                               
               sosMatrix: [5x6 double]                           
             ScaleValues: [6x1 double]                           
        PersistentMemory: false          

cheby1 also design highpass filters, among others. Specify the filter order, passband edge frequency. and the passband ripple to get the filter exactly as required.

d = fdesign.highpass('n,fp,ap',7,20,.4,50)
hd = design(d,'cheby1')
 
d =
 
               Response: 'Highpass'
          Specification: 'N,Fp,Ap' 
            Description: {3x1 cell}
    NormalizedFrequency: false     
                     Fs: 50        
            FilterOrder: 7         
                  Fpass: 20        
                  Apass: 0.4       


hd =
 
         FilterStructure: 'Direct-Form II, Second-Order Sections'
              Arithmetic: 'double'                               
               sosMatrix: [4x6 double]                           
             ScaleValues: [5x1 double]                           
        PersistentMemory: false          

Use fvtool to view the resulting filter.

fvtool(hd)

By design, cheby1 returns filters that use second-order sections. For many applications, and for most fixed-point applications, SOS filters are particularly well-suited.

See Also

butter, cheby2, ellip

ca2tf

cheby2