Column: EMC
The importance of resistors in filter design By Dr Min Zhang, EMC consultant at Mach One Design, and design engineers at REO UK
F
ilters are oſten designed to achieve a certain attenuation in a specified frequency range. We have seen that the impedance of inductive components increases with
frequency, whilst the capacitor’s impedance decreases with frequency. By combining inductors and capacitors, many different types of filters can be built. Although typically filters are designed
using inductors and capacitors because their impedance changes with frequency, resistors are also used for filtering purposes. An ideal resistor has a fixed resistance against frequency, so it might sound odd to use resistors in a filter as they introduce I²R loss.
Linking resistors On a printed circuit board, to ensure signal integrity, resistors are used as series and/or parallel terminations to a transmission line. As shown in Figure 1, they are used to match the impedance of a transmission line system, which is critical for high-speed data communication on a PCB. At the same time, resistors in series with a capacitor or in parallel with an inductor are used to damp the resonance in a system. In a high-voltage system, in order to withstand the voltage on the DC link,
Figure 1: Resistors are used to match the impedance of a transmission line system
Figure 2: Due to capacitance tolerance, it is important to balance capacitors using balancing resistors 12 February 2023
www.electronicsworld.com
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