Least squares filtering

Syntax

hd = design(d,'fircls')
hd = design(d,'fircls','FilterStructure',value)
hd = design(d,'fircls','PassbandOffset',value)
hd = design(d,'fircls','zerophase',value)

Description

hd = design(d,'fircls') designs a FIR Constrained Least Squares (CLS) filter, hd, from a filter specifications object, d.

hd = design(d,'fircls','FilterStructure',value) where value is one of the following filter structures:

'dffir', a discrete-time, direct-form FIR filter (the default value)

'dffirt', a discrete-time, direct-form FIR transposed filter

'dfsymfir', a discrete-time, direct-form symmetric FIR filter

'fftfir', a discrete-time, overlap-add, FIR filter

hd = design(d,'fircls','PassbandOffset',value) where value sets the passband band gain in dB. The PassbandOffset and Ap values affect the upper and lower approximation bound in the passband as follows:

Lower bound = (PassbandOffset-Ap/2)

Upper bound = (PassbandOffset+A/2)

For bandstop filters, the PassbandOffset is a vector of length two that specifies the first and second passband gains. The PassbandOffset value defaults to 0 for lowpass, highpass and bandpass filters. The PassbandOffset value defaults to [0 0] for bandstop filters.

hd = design(d,'fircls','zerophase',value) where value is either 'true' ('1') or 'false' ('0') . If zerophase is true, the lower approximation bound in the stopband is forced to zero (i.e., the filter has a zero phase response). Zerophase is false (0) by default.

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

designopts(d,'fircls')

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

help(d,'fircls')

Examples

The following example designs a constrained least-squares FIR lowpass filter.

h = fdesign.lowpass('n,fc,ap,ast', 50, 0.3, 2, 30);
Hd = design(h, 'fircls');
fvtool(Hd)

The following example constructs a constrained least-squares FIR bandpass filter.

d = fdesign.bandpass('N,Fc1,Fc2,Ast1,Ap,Ast2',...
30,0.4,0.6,60,1,60);
Hd = design(d, 'fircls');
fvtool(Hd)