Controlling RF Interference in Electronic Circuits

Key Takeaways

• RF interference in electronic circuits can be broadly classified as narrowband and broadband interference.

• The techniques commonly used for minimizing RF interference in electronic circuits are either shielding or filtering.

• Compared to RF shields, RF filters stop the conducted RF interference from reaching critical circuit locations.

Different techniques, such as filtering and shielding, can be used to control RF interference in electronic systems

It’s impractical to design a circuit completely free of electromagnetic interference (EMI) or radio frequency interference (RFI). However, EMI and RFI are detrimental to circuit performance.  RF interference includes the unwanted radiofrequency energy radiated from a circuit. It can also include unwanted signals from neighboring external sources, degrading the quality of output signals.  A designer must prevent RFI from interrupting or degrading the signals from one stage to another. Different techniques such as filtering and shielding can be used for controlling RF interference in electronic systems.

Controlling RF Interference

The issues caused by RF interference in electronic circuits are incessant and pose a threat to reliable circuit operation. The chances of critical and sensitive data or signals getting corrupted or lost due to RF interference from internal and external sources are significant.

In a radio communication system, RF interference is the negative impact of unwanted energy caused by emissions, radiations, or inductions. While this problem may seem daunting, controlling RF interference is possible. First, it’s helpful to understand how RF interference is classified.

Types of RF Interference

A wide range of wireless electronic devices, broadcasting, and communication systems utilize the radio spectrum, increasing the probability of RF interference. The RF interference in electronic circuits can be broadly classified as:

Narrowband: Narrowband RF interference is either narrow bandwidth interference or single radio frequency interference. It appears as either continuous waves or modulated continuous waves in electronic circuits.

Broadband: The bandwidth of broadband RF interference is in the range of kilohertz to megahertz. Broadband RF interference occurs either continuously or intermittently in electronic circuits in the form of narrow pulses with short rise and fall times. 

Controlling RF Interference

In electronic circuits, RF interference results from various reasons, including:

• Crowding of devices and communication systems using the RF spectrum
• Compromises made in electronic circuit connections
• Poor enclosures
• Improper design

The main techniques used for controlling RF interference in electronic circuits are either shielding or filtering.

RF Shielding

RF shielding is accepted as a standard method for controlling the radiations and emissions that cause RF interference. RF  shielding protects the critical sections of a circuit from RF interference. It prevents emissions from the circuit and makes the circuit less susceptible to radiation. RF guards are available in different shapes, thicknesses, and materials. The permeability and conductivity of the material play an important role in increasing the efficiency of the RF shield. 

Some RF shielding materials include:

Copper: The high conductivity of copper makes it suitable for RF shielding. It is easy to fabricate copper shields of any shape.

Mu-metal: For protecting sensitive electronic circuits from static and low-frequency electromagnetic fields, a high permeability metal can be used as an RF shield. Mu-metal or alloy of nickel and iron shield RF interferences in hard disks, sensors, etc.

Aluminum: Aluminum RF shields block low-frequency, radio-frequency. It is easy to integrate built-in aluminum shields into circuits. 

RF Filtering

RF filters eliminate radiated emissions from circuits. They protect the circuits from emissions of nearby devices. Internal interference can be limited by incorporating RF filters in electronic circuits. Placing  RF filters in circuits control or prevent the flow of signals of specific frequencies depending on the type and cut-off frequency of the filter.

RF filters are designed specifically to attenuate particular radio frequency noises from the incoming signals. RF filters can be low-pass, high-pass, bandpass, or band-reject filters depending on their frequency characteristics. Compared to RF shields, RF filters stop RF interference from reaching critical circuit locations. RF filters are essential in electronic circuits to achieve electromagnetic compatibility.

Cadence software offers a full suite of design tools to design electromagnetically compatible electronic circuit boards for controlling RF interference in electronics. Sensitive electronic circuits incorporate RF shields and RF filters to prevent RF interference from degrading performance.

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