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EMI filters use two basic elements: series impedances, usually
inductors, and shunt impedances, usually capacitors. These capacitors
and inductors, configured as a low pass filter, reduce unwanted
electrical energy entering or leaving a circuit. The capacitor's
impedance is severely affected by lead inductance. Leaded capacitors
are ineffective filters above the self resonant frequency, usually
greater than a few megahertz, due to parasitic lead inductance.
To achieve high frequency filtering, lead length must be very
near zero. |
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The preeminent filtering challenge is to maintain the required
capacitive shunting performance at high frequencies. It is difficult
to attach capacitors to high current lines while maintaining the
required minimum lead length. |