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Ferrite Beads

Ferrite Beads also known as ferrite chokes are passive devices and they are used to constrict high-frequency signals in electronic components. The ferrite becomes resistive over its intended frequency range and uses up the noise energy in the form of heat.

How do the ferrite beads work?

The ferrite bead is connected in series with the power supply rail and is often combined with the capacitors to ground on either side of the bead. This then forms a low-pass filter network, further reducing the high-frequency power supply noise. Use SPICE (Simulation Program with Integrated Circuit Emphasis) or another similar tool to ensure any anti-resonance peaks caused by ferrite or PCB inductive structure does not violate the target impedance limit.

Ferrite Beads come in two categories:

High-Q Beads - typically used as resonators and must not be used in power isolation circuits
Low-Q Beads - these are also called absorptive beads and they are lossy and make good filter networks because they are designed to absorb high-frequency noise currents and dissipate it as heat

What to consider when choosing Ferrite Beads?

Make sure that any voltage drop does not cause the target supply rail to fall below the recommended operating conditions of the device
The ferrite bead is inductive, therefore do not use it with High-Q decoupling capacitors
Applying ferrite beads correctly can be an effective and inexpensive way to reduce high-frequency noise and switching transients