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a question about the Q of high order LPF

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davidwx

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Since we know that a high order filter can realised by a series of several stages.I am wondering what the exact ralationship between the quality factor of each stage and the quanlity factor of overall.Thank you very much!
 

davidwx said:
Since we know that a high order filter can realised by a series of several stages.I am wondering what the exact ralationship between the quality factor of each stage and the quanlity factor of overall.Thank you very much!
Click to expand...

1.) It is correct that each stage has a different quality factor; however, the relationship between these different Q values depends on the approximation chosen (Butterworth, Chebyshev, Bessel,...)
2.) An "overall" quality factor can be given only in case of a bandpass. But remember this overall Q has another definition as the pole Q for each stage.
LvW
 

LvW said:
1.) It is correct that each stage has a different quality factor; however, the relationship between these different Q values depends on the approximation chosen (Butterworth, Chebyshev, Bessel,...)
2.) An "overall" quality factor can be given only in case of a bandpass. But remember this overall Q has another definition as the pole Q for each stage.
LvW
Click to expand...


suppose that i choose Chebyshev II polynomial to approximate the transfer function,what the relationship i could expect.Thank you again!
 

David, you certainly know that there are several Chebyshev II alternatives depending on
* the degree of the transfer function, and
* the amount of damping in the stop band (zero placement).

More than that, it is not possible to give any relation between the Q values for a selected characteristic. These values result from the transfer function based on the Chebyshev polynoms when it is split into 2nd order expressions.
 

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