Filter Design Toolbox™butter   cheby1
  

ca2tf - Convert coupled allpass filter to transfer function form

Syntax

[b,a]=ca2tf(d1,d2)
[b,a]=ca2tf(d1,d2,beta)
[b,a,bp]=ca2tf(d1,d2)
[b,a,bp]=ca2tf(d1,d2,beta)

Description

[b,a]=ca2tf(d1,d2) returns the vector of coefficients b and the vector of coefficients a corresponding to the numerator and the denominator of the transfer function

d1 and d2 are real vectors corresponding to the denominators of the allpass filters H1(z) and H2(z).

[b,a]=ca2tf(d1,d2,beta) where d1, d2 and beta are complex, returns the vector of coefficients b and the vector of coefficients a corresponding to the numerator and the denominator of the transfer function

[b,a,bp]=ca2tf(d1,d2), where d1 and d2 are real, returns the vector bp of real coefficients corresponding to the numerator of the power complementary filter G(z)

[b,a,bp]=ca2tf(d1,d2,beta), where d1, d2 and beta are complex, returns the vector of coefficients bp of real or complex coefficients that correspond to the numerator of the power complementary filter G(z)

Examples

Create a filter, convert the filter to coupled allpass form, and convert the result back to the original structure (create the power complementary filter as well).

[b,a]=cheby1(10,.5,.4);

 

[d1,d2,beta]=tf2ca(b,a);

% tf2ca returns the % denominators of the % allpasses.

[num,den,numpc]=ca2tf(d1, d2,beta);

% Reconstruct the original % filter plus the power % complementary one.

[h,w,s]=freqz(num,den);

 

hpc = freqz(numpc,den);

 

s.plot = 'mag';

 

s.yunits = 'sq';

 

freqzplot([h hpc],w,s);

% Plot the mag response of the % original filter and the % power complementary one.

See Also

cl2tf, iirpowcomp, tf2ca, tf2cl

  

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