Feedthrough components play a very important role in the EMI suppression of electrical installations and equipment. Feedthrough capacitors and filters are widely employed in EMI/RFI suppression circuits, power converters, power supplies, telephone exchanges, and base stations.
Feedthrough Filters
Feedthrough is one of the key sources of electrical noise in signal transmission. It is especially
a problem in Si/ZnO Surface Acoustic Wave (SAW) devices. The feedthrough is because input and output connectors effectively form a capacitor so that electromagnetic energy can be coupled directly between them. The induced feedthrough creates unwanted amplitude and phase ripples in the transmitted signal.
The easiest way of preventing EMI is to enclose the electrical equipment (if possible) in a metal case. This is popularly known as ‘Faraday Cage’ and is good at minimizing Radiated Interference (RMI). However, most pieces of equipment require input-output connections such as power cables, signal, and control lines which may act as antennae for picking up or radiating interference.
Using Feedthrough Components (Filters and Capacitors) is an important solution to attenuate the undesired EM/RF noise. Feedthrough components can safely carry high frequency electrical signals through PCBs or enclosures. They act as a bypass and can carry either high current or high voltage signals.
Therefore, most electrical and electronic systems need a sequence of Inductor-Capacitor (LC) filters to remove EMI. These components are called Feedthrough (FT) Capacitors and FT Filters.
Interference entering or leaving the equipment can be eliminated using feedthrough EMI filters mounted in the wall of a shielded case. Any incoming or outgoing cables would then pass through these filters. Power or wanted signals would pass through these filters unaffected. Only higher frequency interference will be blocked. These filters will reduce both emissions and susceptibility. They are one of the most reliable solutions for high frequency and high current filtering applications.
Feedthrough Capacitors are an elementary, cost-effective option. For higher performance over a broad range of frequencies, feedthrough filters are used. Filters perform better than capacitors when the noise source impedance is < 50 Ohm.
Feedthrough capacitor sample schematic
A Feedthrough Capacitor is a feedthrough terminal that provides the desired value of capacitance between the conductor and the metal chassis through which the conductor is passing. This capacitor is primarily used for bypass purposes in high frequency circuits.
Normal two terminal capacitors resonate with their lead inductance in the region 1-10MHz. So they may not be effective in noise suppression above a few MHz. However, feedthrough capacitors have no major resonance as they have no lead inductance and the performance of these units continues to increase with frequency. In a feedthrough capacitor, the current carrying conductor is connected to an electrode that runs through the center of the component. The second electrode is connected to the case. This concentric geometry is responsible for its excellent performance characteristics, both at low and high frequencies.
The most common designs of feedthrough capacitors are tubular feedthrough types.
Feedthrough Filter Connection
A Feedthrough device consisting of an inductor positioned between two capacitors connected to the ground. L, T, LL, and Pi are different types of feed-through filters. They are very effective in providing filtering in high frequency ranges (> 1 GHz). They also provide EMI protection in standard, high and extended performance ranges.
C Filter – Just a feedthrough capacitor that has low self-inductance. Works by shunting the high frequency noise to the ground. Suitable when both source and load impedances are high.
L-C Filter – Inductive element combined with a capacitor. Suitable when the source and load have contrasting impedances (one low, the other high).
Pi Filter – 2 capacitors and an inductive element in between. Suitable when both source and load impedances are high.
T Filter – 2 series inductive elements separated by a feedthrough capacitor. Suitable when both source and load impedances are low.
Multi-element filters – 3 or more elements in combination such as L-C-L-C-L filters. The insertion loss increases exponentially as more elements are added.
Insertion Loss is a relative measure of the filter’s attenuation characteristics, measured in decibels (dB). It is the ratio of noise without a filter to that with a filter installed. The insertion loss performance is used to determine the appropriate filter by gauging signal attenuation at any given frequency. However, this is only indicative. Actual performance in service will vary depending on the overall circuit characteristics.
The factors that might influence the insertion loss are – filter configuration, source, and load impedances, load current, shielding quality, earthing impedance, dielectric materials used.
Image courtesy – Passive-components.eu
Filters Insertion Loss
EMISINDIA has a wide range of Standard Feedthrough Capacitors and Filters. EMIS feedthrough components provide high insertion loss (attenuation) to the wide range of frequencies up to 1GHz. They comply with standard CAN / CSA-E60384-14:09. Feedthrough components are available up to 600A in both AC and DC.
Customized Feedthrough Components
EMIS also develops Customised Feedthrough components based on the configuration, capacitor rating, electrical parameters/characteristics, mechanical dimensions, and mounting arrangements of the customer.
Feedthrough Filters
Multiple products are available for different purposes.
Find more information in the product data sheet here.
Multiline filter configuration (two lines, three lines, and four lines) available. Also available with Surge Suppressor.
Find more information in the product data sheet here.
The EMC Filters may be used only for their intended application within the specified values in low voltage networks in compliance with the instructions given in the datasheets.
Feedthrough components from EMIS are widely used in several industry areas. They are specially designed to handle all kinds of high frequency EMI suppression. Some industry application areas are listed below.
With the backing of a strong design team and a NABL accredited in-house testing facility, EMIS can offer custom feedthrough capacitor and filter solutions to your design challenges with ease.
EMISINDIA is a leading service provider of Electromagnetic Compatibility (EMC) and Electromagnetic Interference (EMI) Engineering and Compliance Services. Apart from comprehensive EMI/EMC Testing Facilities, we also offer expert consultancy support for engineering, design analysis, and technical training. Our endeavor is to provide our customers all EMI related solutions under one roof. Feel free to get in touch with us.
An integral part of the content creation team at EMIS INDIA, Anuradha is a corporate trainer in the IT/telecom domain with over 18 years of experience. She served in senior technical and management positions in Huawei and TCS for 10+ years
