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Hello, I have got a theory on this link of filters http://ece-www.colorado.edu/~ecen2260/slides/FilterSlides.pdf It gives in a formula a relationship between wo and wc. wo should be chosen in such a way that the desired cut-off frequency is got; here is the formula wo=wc*((2^1/n)-1)^1/2 where n is the filter order. When i fill in this formula i get for wc=8.2 MHz, wo#.43MHz. When i used the wo value in my code i get at -3dB a reading of 9Mhz(instead of 8.2 Mhz). Can one check that theory and tell me if my approach is correct? Thx ===== Sylvianne |
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bessel filter
Started by ●March 12, 2003
Reply by ●March 12, 20032003-03-12
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Hi, Matlab besself or besselap function's returned transfer function does not seem to get the cutoff freq exactly at -3db. So you can try the follg. 1. Get the poles of the analog bessel filter from some filter design book. 2. Since you used bilinear transformation earlier, do prewarping before using your cutoff frequency in the analog domain. (like W=tan(w/2)) 3. Do bilinear transformation to get digital filter. (you can use 'bilinear' function) But if you do bilinear transformation you will loose the linear phase properties of bessel filter. So you can try other analog to discrete conversion methods also. Navan --- Sylvianne Tameze <> wrote: > Hello, > > I have got a theory on this link of filters > http://ece-www.colorado.edu/~ecen2260/slides/FilterSlides.pdf > It gives in a formula a relationship between wo and > wc. > wo should be chosen in such a way that the desired > cut-off frequency is got; here is the formula > wo=wc*((2^1/n)-1)^1/2 where n is the filter order. > When i fill in this formula i get for wc=8.2 MHz, > wo#.43MHz. > When i used the wo value in my code i get at -3dB a > reading of 9Mhz(instead of 8.2 Mhz). > Can one check that theory and tell me if my approach > is correct? > > Thx > > ===== > Sylvianne __________________________________________________ |
