Optimize Your Filter Design Using EMI Filter Simulation

Cadence System Analysis

Key Takeaways

EMI filter simulation is a computer-based simulation method where the designer can simulate the response of an EMI filter.
EMI filter simulation can provide a frequency sweep feature, where the signal of interest is superimposed with high-frequency signals.
The parametric sweep, an extension of EMI filter simulation, can help in identifying the best components for a filter circuit.

Circuit simulation using a simulation tool

Circuit simulation is helpful when designing EMI filters

Designing perfect EMI filters for power supplies or power converters is a challenging task. Passive EMI filters are designed for a passband and stopband. They reject frequency components above the cut-off frequency, suppressing the interference from reaching the loads.

Simulation tools are helpful when designing EMI filters. Circuit simulation prevents hardware iterations in EMI filters, and the design process becomes less excruciating with them. EMI filter simulation is one computer-aided method of designing real EMI filters that are close to ideal filters.

Noise Suppression for Improved System Performance

Switched-mode power supplies are a reliable source of power for industrial, automotive, medical, and consumer applications. Switched-mode power supplies are based on power electronic converters, and these converters generate noise, especially conducted noise, broadband noise, and high-frequency noise. The noises generated in circuits can be categorized as either common-mode or differential mode noise, which leads to interference in the load and source sides. It is very important to suppress these noises, as it affects the performance of the system.

Using EMI Filters to Suppress Noise

Using EMI filters is one way to suppress noise. These filters are designed to limit certain frequencies from reaching the load and source sides. Each EMI filter is associated with frequency response, and when the input signals undergo variation, they often show transient response. The filter design needs to satisfy the suppression of unwanted frequency components in the circuit and its response should match with this given task.

EMI Filter Simulation

EMI filter simulation is a computer-based method where the designer can simulate the response of an EMI filter before going into the hardware implementation phase. The goal of EMI filter simulation is to verify the frequency response of a filter and confirm that it suppresses the desired frequency or range of frequencies.

EMI filter simulation identifies how efficient the filter is at minimizing noise present in the circuit. For example, consider a power circuit in which the noises present (and their frequencies) are known. In the design phase of the filters for such circuits, imagine that the designer is clear about the specific frequency, or range of frequencies, the filter needs to suppress as well as the components to be selected. In such cases, EMI filter simulation verifies the frequency response of the filter to make sure it does the job perfectly.

Types of EMI Filters

EMI filters can be active or passive, and EMI filter simulation can work on both types of filters.

Passive EMI filters are made of passive components—capacitors and inductors.

Active EMI filters are based on active devices, utilizing the technique of anti-noise cancellation. Active filters generate the same noises that are present in the circuit, but opposite in phase. The combination of the noises in the circuit and the anti-noise from the active filters nullify the noise effect in the circuit.

What Does EMI Filter Simulation Help With?

EMI filter simulation helps us to identify multiple resonances due to parasitics and coupling from the transfer function of the filter. The filter characteristics under various noise frequencies and resonance conditions can be visualized using EMI filter simulation. The effectiveness of damping resistors in minimizing the resonances can also be studied from EMI filter simulation.

Frequency Sweeps and Transfer Functions

For linear filters, the transfer function of the filter provides information on its frequency response. EMI filter simulation can provide a frequency sweep feature, where the signal of interest is superimposed with high-frequency signals. The input signals to the EMI filter are given an initial frequency sweep, from DC to high frequency, to check the resonance in the EMI filter. The parasitics associated with EMI filters are responsible for the creation of resonance conditions.

High-Frequency Spikes in Output Signals

In certain cases, damping resistors may damp out the resonant frequency of interest, but get coupled with other components or parasitics in the circuit. This may lead to the generation of other high-frequency spikes in the output signal. This is a serious concern when selecting the components for a filter. The parametric sweep is an extension of EMI filter simulation, and it can help in identifying the best components for the filter circuit.

Why Use EMI Filter Simulation?

EMI filter simulation allows designers to evaluate and optimize EMI filter designs, as it is the best simulation tool to understand conducted noise, coupling effects, and resonance in filter designs. This type of simulation helps designers avoid hardware trial-and-error iterations and speed up the time it takes to deliver a completed product.

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