firrcos (Signal Processing Toolbox)

Raised cosine FIR filter design

Syntax

b = firrcos(n,F0,df,fs)
b = firrcos(n,F0,df,fs,'bandwidth')
b = firrcos(n,F0,df)
b = firrcos(n,F0,r,fs,'rolloff')
b = firrcos(...,'type')
b = firrcos(...,'type',delay)
b = firrcos(...,'type',delay,window)
[b,a] = firrcos(...)

Description

b = firrcos(n,F0,df,fs) or, equivalently,

b = firrcos(n,F0,df,fs,'bandwidth') returns an order n lowpass linear-phase FIR filter with a raised cosine transition band. The filter has cutoff frequency F0, transition bandwidth df, and sampling frequency fs, all in hertz. df must be small enough so that F0 ± df/2 is between 0 and fs/2. The coefficients in b are normalized so that the nominal passband gain is always equal to 1. Specify fs as the empty vector [] to use the default value fs = 2.

b = firrcos(n,F0,df) uses a default sampling frequency of fs = 2.

b = firrcos(n,F0,r,fs,'rolloff') interprets the third argument, r, as the rolloff factor instead of the transition bandwidth, df. r must be in the range [0,1].

b = firrcos(...,'type') designs either a normal raised cosine filter or a square root raised cosine filter according to how you specify of the string 'type'. Specify 'type' as:

'normal', for a regular raised cosine filter. This is the default, and is also in effect when the 'type' argument is left empty, [].
'sqrt', for a square root raised cosine filter.

b = firrcos(...,'type',delay) specifies an integer delay in the range [0,n+1]. The default is n/2 for even n and (n+1)/2 for odd n.

b = firrcos(...,'type',delay,window) applies a length n+1 window to the designed filter to reduce the ripple in the frequency response. window must be a length n+1 column vector. If no window is specified, a rectangular (rectwin) window is used. Care must be exercised when using a window with a delay other than the default.

[b,a] = firrcos(...) always returns a = 1.

Examples

Design an order 20 raised cosine FIR filter with cutoff frequency 0.25 of the Nyquist frequency and a transition bandwidth of 0.25:

h = firrcos(20,0.25,0.25);
freqz(h,1)

See Also

fir1, fir2, firls, firpm

firpmord flattopwin