APPLICATION NOTE
2
Impedance of a bead depends on the material and dimensions of the bead.
In the following Fig.2, Bead #2 has more inductance than Bead #1.
Figure 2: Impedance of Bead
Two different approaches to model Ferrite Beads in PSpice has been described below.
Model Ferrite Beads in PSpice - Approach 1
Ferrite beads used for power supply decoupling represent a difficult modeling problem for those involved in
SPICE circuit simulations. The bead's frequency-dependent nonlinear and non-monotonic behavior are
particularly difficult to model.Eventually, the best recourse is to use simple L-R type equivalent circuit models.
Accurate modeling and simulation of ferrite beads over a wide range is possible. To model the bead, a voltage-
controlled current source (VCCS) behavioral model is used in such a way that the source's terminals appear as
an impedance. The source's current is controlled by its terminal voltage as follows:
Thus, the terminal impedance (Z) is the reciprocal of the source's scale factor (K). The listing illustrates this
concept for a sub circuit model of the Fair-Rite 2673000101 ferrite bead.Data is entered into the table as
frequency, magnitude of 1/Z in decibels, and the angle of 1/Z in degrees.
.SUBCKT BEAD73 1 2
GBEAD 1 2 FREQ { V(1, 2) }= ((1K,40.5,-89.9)
+ (10k, 20.6, -89.5)
+ (100k, 0.9, -80.5)
