[SOLVED] Chebyshev Filters - example

[matusel]

Hello everybody i'm studiing the Chebyshev Filters and i would like to know if someone can post an example of a third order Chebyshev Filter.

 

[rfmemo]

what is the frequency specification of your filter?

 

[FvM]

Just an example

 

[matusel]

Ok thankyou very much I needed this example because I have a doubt. In my book they say that the amplitude of a cebyshev filter oscillates in the pass band but the question is, if the transfer function has just poles how can the module (bode plot) oscillate (see ripple) ?
To oscillate there should be also zeroes!! In the oscillation the poles move the amplitude down of 20dB and the zeroes move it up...what is my mistake?

 

[FvM]

A Chebyshev type I filter has only poles, one real and a complex pair in case of 3rd order. Your simplified assumption about relation of poles/zeros and magnitude characteristic doesn't aplly to complex pole pairs, I think.

 

[matusel]

Thank you FvM And there is no way/rules to draw a bode diagram of amplitude of a couple of complex poles ?

 

[FvM]

I think, you can't sketch the magnitude without considering the pole quality factor. Below is an example of a second order Cheybyshev, which represents basically one complex pole pair.

 

[matusel]

Thank I think I've finally undersood