23/05/2026
EMC/EMI Control Techniques in PCB Design
As IC integration continues to increase, electronic devices become smaller and signal speeds grow faster, EMI (Electromagnetic Interference) issues in electronic products are becoming more serious than ever. From the perspective of system-level EMC/EMI engineering, handling EMI problems during the PCB design stage is the most effective and lowest-cost solution for achieving electromagnetic compatibility compliance.
This article introduces practical EMI control techniques for digital PCB design.
Principles of EMI Generation and Suppression
EMI occurs when electromagnetic interference sources transfer energy to sensitive systems through coupling paths. The three main coupling mechanisms are:
Conducted interference through wires or common ground lines
Radiated interference through space
Near-field electromagnetic coupling
The impact of EMI includes:
Reduced signal integrity
Circuit malfunction
Equipment instability
Failure to meet EMC compliance standards
To suppress EMI effectively, digital circuit PCB design should follow these principles:
Divide EMC/EMI requirements into subsystem and PCB-level targets for hierarchical control
Control the three EMI elements:
Interference source
Energy coupling path
Sensitive receiver system
Maintain a stable and flat frequency response to ensure reliable circuit operation
Start EMC/EMI considerations from the earliest design stage to reduce overall development cost
EMI Control Techniques for Digital PCB Design
Different EMI problems require different solutions. In digital PCB design, EMI can be controlled from the following aspects.
Component Selection
The first step in EMI-aware PCB design is proper component selection.
Device switching speed has a major impact on EMI performance. For example, replacing a device with a 5 ns rise time by one with a 2.5 ns rise time can increase EMI radiation by approximately four times.
The radiated EMI intensity is proportional to the square of frequency. The maximum EMI frequency, also called EMI emission bandwidth, depends on signal rise time rather than signal frequency:
The radiated EMI frequency range typically extends from 30 MHz to several GHz. At these frequencies, wavelengths become very short, meaning even short PCB traces can behave like antennas and radiate interference.
When EMI levels become excessive, circuits may lose normal functionality.
Therefore, under the condition that circuit performance requirements are satisfied:
Use lower-speed ICs whenever possible
Select appropriate driver and receiver circuits
Avoid unnecessarily fast edge rates
Influence of Package Type
Component package parasitics also significantly affect EMI performance.
All component leads contain parasitic inductance and parasitic capacitance, which become increasingly important in high-speed PCB design.
Generally:
SMD components have lower parasitic parameters than through-hole components
BGA packages usually have lower parasitics than QFP packages
As a result, package selection is also an important factor in reducing EMI radiation in modern electronic systems.
