Is there a general form of transfer function (with peak frequency \$\omega_m\$ and quality factor \$Q\$) relevant for any type of bandpass filter ?

  • \$\begingroup\$ a bandpass filter has two cutoff frequencies! \$\endgroup\$ – stevenvh May 14 '12 at 12:00
  • \$\begingroup\$ well I meant the peak frequency, the frequency at which the gain is maximum \$\endgroup\$ – snickers May 14 '12 at 12:02
  • \$\begingroup\$ Some bandpass filters have multiple peaks, like a Chebychev for example. \$\endgroup\$ – Olin Lathrop May 14 '12 at 12:04
  • \$\begingroup\$ @snickers - even without the multiple peaks (Olin's comment) the center frequency isn't enough to know the bandwidth. \$\endgroup\$ – stevenvh May 14 '12 at 12:06
  • \$\begingroup\$ @snickers - example of the frequency response of a Chebychev filter: cnx.org/content/m16895/latest/c92.png \$\endgroup\$ – stevenvh May 14 '12 at 12:09

No. Whilst a standard second-order bandpass section can be defined in this way ...

\$H(s) = \dfrac{\dfrac{\omega_m}{Q}s}{s^2+\dfrac{\omega_m}{Q}s+\omega_m^2}\$

... it is also possible to have a second-order bandpass filter with the same characteristic frequency and Q but with a different transfer function. This previous question which addresses a filter with a stop-band attenuation of 1 is a case-in-point.

Furthermore, higher-order filters will require more than just these two parameters to define them since there are more coefficients.


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