Insertion Loss in EMI Filters
Electromagnetic interference (EMI) filtering is essential to equipment design. The key to choosing a high-performance filter is knowing the basics of EMI filter insertion loss.
What Is Insertion Loss?
Insertion loss measures how much an EMI filter weakens a passing signal at a given frequency. It denotes how well the filter can eliminate unwanted noise from a circuit.
Insertion loss in EMI filters is the ratio of the input signal to the output signal. It's dependent on frequency and often changes over various orders of magnitude in the filter's useful frequency range, making it most easily expressed in decibels.
Why Is Insertion Loss Important?
Insertion loss plays a crucial role in the design and development of high-frequency devices — in this case, EMI filters. As a metric, this efficiency measurement makes a valuable guide to selecting an EMI filter that meets unique performance requirements. It's a good rule of thumb to select an EMI filter with insertion loss performance that meets the device's requirements, typically high insertion loss indicates higher performance.
High Insertion Loss Measurement
There are various ways you can measure insertion loss, such as a spectrum analyzer. This device measures and displays signal strengths with varied frequencies within its spectrum, or frequency range. It displays the full signal spectrum and other characteristics like noise, modulated width, and spurious signals. You can use a spectrum analyzer to calculate loss measurement.
A line impedance stabilization network (LISN) is used in susceptibility and radiofrequency emission testing for EMI test standards. LISN can calculate insertion loss while taking impedance into account, then plot the data from other measures on a graph.
Factors That Impact Insertion Loss
Numerous characteristics influence EMI filter insertion loss, including:
- Electrical configuration: A filter's electrical configuration, or capacitor and inductor combination, should optimize filter performance for a specific source and load impedance situation. Insertion loss performance is usually dependent on component characteristics, which you can find in datasheets.
- Source and load impedance: Source and load impedance usually has different published values than insertion loss figures and may differ from what the figures imply, resulting in insertion loss fluctuations.
- Load current: How load current affects EMI filter insertion loss depends on the filtering element properties. Filters with inductive elements might experience considerable insertion loss reductions where ferrite inductors saturate currents.
- Earthing impedance: Grounding systems provide a low impedance path for currents to the earth.
- Shielding integrity: Shielded rooms have multi-circuits for achieving high insertion loss and leakage currents for high common-mode insertion loss.
Low Conducted Emissions Testing and Filter Insertion Loss
Conducted emissions are the noise components that a device or subcircuit generates and channels to another device. These emissions must remain low or they may cause issues within other devices.
Equipment must adhere to applicable EMI regulations and conducted emissions requirements. Insertion loss performance is crucial to this equipment compliance. When you conduct insertion loss testing to establish the raw conducted emissions data, you can determine the frequency and extent to which the unit requires suppression.
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