Difference in Chebyshev filter

Question

Chin Wei Chang 2017-1-9

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/319684-difference-in-chebyshev-filter

编辑： Chin Wei Chang 2017-4-10

采纳的回答： Star Strider

在 MATLAB Online 中打开

I want to realize Chebyshev filter by two ways ,MATLAB function and formula

Type = 6, ripple = 10db , cutoff frequency=300Hz

This is using MATLAB function "cheby1" to simulate

[b,a] = cheby1(6,10,0.6);  % 0.6=300/(1000/2)
figure(); 
freqz(b,a,[],1000);

This is output

And the following code is totally the same as Chebyshev filter' formula

N = 6; 
ripple = 10; 
wc = 300; 
w1 = 0 :wc; 
w2 = wc :500; 
V1 = cos(N*acos(w1/wc)); 
V2 = cosh(N*acosh(w2/wc)); 
epsilon = sqrt( ( 10^(0.1*ripple) ) -1); 
H1 = 1 ./ sqrt( 1 + (epsilon * V1).^2 ); 
H2 = 1 ./ sqrt( 1 + (epsilon * V2).^2 ); 
plot(w1 , 20*log10(H1)); 
hold on, 
plot(w2 , 20*log10(H2));

This is output

I don't know why these two figures are different,

how can I fix this?

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Star Strider 2017-1-9

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/319684-difference-in-chebyshev-filter#answer_249944

They don’t look different to me. The difference is that the cheby1 code implements a discrete filter using the bilinear transformation. Your code designs a continuous filter.