Patent ID: 7657564

Claim:
A method for selecting a desired ferrite bead from a plurality of ferrite beads for a filter to avoid a peak value from occurring in a frequency response curve of the filter, the method comprising the steps of: (a) building an equivalent model database comprising parameters of equivalent models of the plurality of ferrite beads, the parameters comprising an inductance and a capacitance of a corresponding equivalent model of each ferrite bead; (b) calculating parameters of the desired ferrite bead in the filter based on parameters of the filter, the parameters of the desired ferrite bead comprising an inductance, a capacitance, and a resonant frequency, wherein the inductance of the desired ferrite bead in the filter is obtained as follows: L = R 2 ⁢ C ′ Q 2 where L denotes the inductance of the desired ferrite bead, R denotes a load impedance of the filter, C′denotes a capacitance of the filter, and Q denotes a quality factor of the filter, wherein the capacitance of the desired ferrite bead in the filter is obtained as follows: C = C ′ 10 - A 20 - 1 where C denotes a capacitance of the desired ferrite bead, A denotes an attenuation constant of the filter, wherein the resonant frequency of the desired ferrite bead in the filter is obtained as follows: F = 1 2 ⁢ π ⁢ LC where F denotes the resonant frequency of the desired ferrite bead; (c) comparing the resonant frequency calculated in step (b) with a desired resonant frequency of the filter; if the resonant frequency calculated in step (b) equals or approaches the desired resonant frequency, going to step (e); if the resonant frequency calculated in step (b) does not equal or approach the desired resonant frequency, going to step (d); (d) adjusting parameters of the filter, then returning to step (b) to obtain different parameters of the desired ferrite bead; (e) searching the equivalent model database for an inductance and a capacitance respectively equaling or approaching the inductance and the capacitance calculated in step (b); if the inductance and capacitance do not exist in the database, going to step (f); if the inductance and capacitance exist, going to step (g); (f) adjusting parameters of the filter, then returning to step (b) to obtain different parameters of the desired ferrite bead; (g) selecting the desired ferrite bead with the searched inductance and capacitance in the database for the filter for avoiding the peak value in the frequency response curve of the filter.