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Using EMC Grounding Techniques to Build Noise Immune Circuits

Author Cadence System Analysis

Key Takeaways

  • EMC grounding creates an equipotential point or plane that serves as the reference point for all other components in the circuit. It is the low impedance path in the circuit for the current to return to the signal source. 

  • The three main objectives of EMC grounding are to minimize coupling interferences, emissions, and susceptibility.

  • When designing grounding systems, it is important to consider the signal's frequency, the path's effective impedance, current amplitude, and the maximum noise voltage that the circuit can withstand. 

EMC grounding symbol

EMC grounding techniques reduce EMI effects in circuits

Engineers work hard to ensure suitable electromagnetic compatibility (EMC) performance from a circuit while the circuit is still in the design phase. Addressing EMI after product development is a complicated and costly process. For this reason, product development teams consider EMC performance as one of the most important goals in circuit design. Engineers utilize EMC filters, circuit partitioning, EMI shielding, minimum radiation design, and grounding to reduce EMI effects. EMC grounding techniques reduce the EMI from electromagnetic fields, common impedance, and interferences from capacitive and inductive coupling.

Let’s learn more about the different types of EMC grounding techniques and how they reduce noise in circuits. 

Proper and Improper EMC Grounding 

EMC grounding creates an equipotential point or plane that serves as a reference point for all of a circuit's componentry. The low impedance path in the circuit allows the current to return to the source of the signal. Grounding provides less signal interference and makes the circuit electromagnetically compatible when the signals are not lost and return to the source.

Proper grounding effectively increases the EMC performance of a circuit, whereas improper grounding has the opposite result. Improperly grounding circuits creates common-mode noise in the circuit. The high impedance of the grounding path and the large area of ground loops aggravates the emissions in the circuit, resulting in more EMI.

The design of the grounding system in a circuit needs to be as compact and local as possible. Proper grounding design includes maintaining the lowest ground impedance and confining the ground loops to the smallest possible area. In properly grounded circuits, the induced voltages at critical locations remain low, the interference voltages at critical areas are minimized, and the desired signals remain immune from noise. 

Design Objectives of EMC Grounding

The three main objectives of EMC grounding are to minimize coupling interferences, emissions, and susceptibility. While designing the grounding system, signal characteristics and allowable noise levels should be considered. The allowable noise levels in circuits are usually identified from the international standards given by regulatory bodies, which are:

  • CISPR
  • FCC
  • IEEE 
  • IEC

When designing grounding systems, it is important to consider the circuit's signal frequency, the effective impedance of the path, current amplitude, and the maximum noise voltage the circuit can withstand. These objectives should be kept in mind when choosing one of the many EMC grounding techniques.

EMC Grounding Techniques

EMC grounding techniques are used in circuit boards, cables, and large systems. They are a cost-effective way to protect against EMI and noise. EMC grounding techniques are chosen based on a circuit's configuration and its frequency of operation. It is common practice to use wires for EMC grounding in low-frequency circuits and co-axial or conducting cables in high frequency or high-speed digital circuits.

EMC grounding can be classified into four broad categories, which are:

  1. Single-point grounding - The individual circuits in this type of EMC grounding are connected to a common ground point. This type of grounding is suitable for low-frequency circuits below 1MHz and prevents common-mode impedance coupling. Single-point grounding is implemented either as series-single-point grounding or parallel-single-point grounding.
  2. Multi-point grounding - Each circuit is grounded separately to the nearest ground plane of low impedance. Multi-point grounding is preferred in high-frequency circuits operating above 10 MHz.
  3. Hybrid grounding - Hybrid grounding utilizes single-point grounding for low-frequency circuits and multi-point grounding for high-frequency operating circuits. 
  4. Floating ground - There is no coupling loop between the circuits and the ground plane in a floating ground.

In a single circuit board, there can be subsystems working on different frequencies. In large circuit boards handling analog, digital, or mixed signals of different frequencies, an efficient circuit designer must analyze multiple circuit characteristics such as current, frequency, and noise levels before deciding between single-point, multi-point, or hybrid grounding. EMC grounding techniques are a cost-effective way to achieve better EMC performance. Cadence’s PCB design software helps designers create proper grounding systems in electronic circuits. 

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