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equiripple - Equiripple single-rate FIR filter from specification object

Syntax

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

Description

hd = design(d,'equiripple') designs an equiripple FIR digital filter using the specifications supplied in the object d. Equiripple filter designs minimize the maximum ripple in the passbands and stopbands. hd is a dfilt object

hd = design(d,'equiripple',designoption,value,designoption,
...value,...) returns an equiripple FIR 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 equiripple, refer to the command line help system. For example, to get specific information about using equiripple with d, the specification object, enter the following at the MATLAB prompt.

help(d,'equiripple')

Examples

First create a lowpass equiripple filter. Assume the data is sampled at 10,000 Hertz. The passband frequency is 500 Hertz with a stopband frequency of 700 Hz. The desired passband ripple is 1 dB with 60 dB of stopband attenuation.

Fs=10000;
d=fdesign.lowpass('Fp,Fst,Ap,Ast',500,700,1,60,10000);
Hd=design(d,'equiripple');

Displaying the filter in FVTool shows the equiripple nature of the filter.

The next example designs a highpass equiripple filter with a direct-form transposed structure by specifying the filterstructure argument. To set the design options for the filter, use the designopts method and options object opts.

d=fdesign.highpass;
opts=designopts(d,'equiripple')

opts = 

    FilterStructure: 'dffir'
      DensityFactor: 16

opts.FilterStructure='dffirt'

opts = 

    FilterStructure: 'dffirt'
      DensityFactor: 16
opts.densityfactor=20

opts = 

    FilterStructure: 'dffirt'
      DensityFactor: 16
      densityfactor: 20 
Hd=design(d,'equiripple',opts)
 
Hd =
 
     FilterStructure: 'Direct-Form FIR Transposed'
           Numerator: [1x45 double]               
    PersistentMemory: false               

See Also

design, designmethods.

ellipord

eqtflength

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