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Ferrite Data Line Filters for Noise Suppression

Key Takeaways

  • One of the methods to mitigate noise is to use filters in data lines. 

  • Ferrite data line filters are one of the successful ways to implement filtering techniques that use external magnetics.

  • Surface mount ferrite beads are employed for attenuating noises in data lines laid out on PCBs.

  External magnetics on data lines

Data line filtering is one solution to minimize the impact of noise sources on data lines

As data rates explode with new digital technologies, data lines continue to be affected by EMI and noise. The frequency of the noise in these data lines increases with the switching speed and data rates. To achieve signal integrity and communication reliability, it is important to mitigate disturbances from the data line.

Data line filtering is one solution to minimize the impact of noise sources on data lines. The use of ferrite data line filters is one of the noise suppression methods that filter out high-frequency noises disturbing data lines. In this article, we will explore ferrite-based data line filtering.   

Data Line Noise Sources 

Noise is a major concern in low signal level data line equipment, and it is common for data line equipment to experience failure due to noise sources. Low signal level data line equipment coexists with noise sources, such as power converters, semiconductor devices, magnetic modules, and control or logic circuits, which introduce a significant amount of noise into data lines. Power converters predominantly produce harmonics of switching frequency and wideband noises, which influence the data transmission through data lines.

Thermally-induced noises in semiconductor devices, contact noises generated from joining dissimilar materials, and shot noises from electron-hole movements are some of the noise sources responsible for data loss or errors. The ringing noise produced by magnetic components such as transformers used in the auxiliary modules functioning, along with low signal level data equipment, is significant in producing data line noises. The switching from high to low levels and vice versa in logic or control circuits is detrimental to the signal transmission over data lines. Power line noises and radiated noises are also capable of disturbing signals in the data lines of low signal level data equipment. Rigorous noise limits are set by regulatory bodies to protect data lines in digital equipment from noise and EMI effects. One method of mitigating noise is to use filters in data lines. 

Data Line Filtering

A practical solution to protect data lines is to prevent them from being affected by noise rather than eliminating the noise sources. Locating and filtering noise from reaching the data line reduces the severity of the noise sources. Filtering can effectively handle conducted and radiated noise as well as safeguard data line signals from noise sources. 

Ferrite Data Line Filters

Ferrite data line filters are one of the best filtering techniques that use external magnetics. The data lines deal with logic transitions, and the influence of noise causes data errors at the receiving end. Attenuating or filtering high-frequency noise from reaching the data lines prevents false states or corrupted logic transitions. Filtering of the data lines using external magnetics creates a magnetic field around the data line and prevents high-frequency noise from affecting data signals.

The basic principle of using external magnetics for filtering is to increase the inductance of the data line loop. But, why not use data line looping for increased inductance?  The looping of the data line cables increases the inductance; however, to achieve a considerable inductance, several loops are required, as the looping depends only on air as the medium to contain the magnetic field. Magnetic materials, especially ferrite materials, can improve the inductance with minimal looping. Ferrite beads are excellent in mitigating data line noises.

Ferrite Beads for Noise Suppression

Ferrite materials are utilized for both common mode and differential mode filtering. The data line cables inserted through the cylindrical hollow ferrite cores constitute a single turn and increase the inductance, which offers data line filtering. The inclusion of ferrite beads in the data line cables performs EMI and noise suppression. Ferrite beads accumulate unwanted energy and either dissipate it as heat energy or radiate it. Surface mount ferrite beads are employed for attenuating the noise in data lines laid out on PCBs. Ferrite-based common-mode chokes are also used for data line filtering where a high level of impedance is required.

The type of ferrite data line filter employed in low signal level data equipment to mitigate noise depends on the level of impedance. Irrespective of the filtering mechanism used, Cadence’s PCB design and analysis software can help designers create high and low signal level systems.

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