Electromagnetic interference (EMI) suppression is critical to circuit board design, especially in electronic devices, as it prevents electromagnetic radiation and electromagnetic susceptibility problems. Here are some common methods and techniques used for EMI suppression:
1、Ground Planning and Separation:
Use proper ground planning, including ground plane design, to ensure that ground loops are short and clean.
Separate the ground lines of digital and analogue circuits to reduce mutual influence.
2、Shielding and Surrounding:
Use shielded boxes or shields to surround sensitive circuits to reduce the effects of external interference.
Use shields in high-frequency circuits to prevent radiation.
Use shielded cables to reduce conducted interference.
3、Filters:
Use filters on power and signal lines to stop high-frequency noise from entering or radiating from the circuit.
Add input and output filters to reduce conducted and radiated interference.
4、Layout and wiring:
Carefully plan board layout to minimise high frequency signal paths and reduce loop area.
Minimise the length of signal lines and use differential signal transmission to reduce conducted interference.
Use the ground plane to reduce the inductance of the loop to reduce high frequency noise.
5、Windings and inductors:
Use inductors and windings on signal lines to suppress high frequency noise.
Consider using power line filters and common mode inductors on power lines.
6、Grounding and Ground Plane:
Use low impedance grounding points and ensure that all grounds on the board are connected to the same point.
Use ground planes to provide low impedance loops to reduce radiated and conducted interference.
7、Wiring and Level Separation:
Separate high-frequency and low-frequency signal lines and avoid them crossing on the same layer.
Use multi-layer PCBs in order to separate different types of signals on different layers and reduce mutual interference.
8、EMC Testing:
Perform electromagnetic compatibility (EMC) testing to verify that the design meets specified EMI standards.
Pre-testing is performed early in product development so that problems can be corrected early.
9、Material Selection:
Select materials with good shielding characteristics, such as metals with high conductivity or special shielding materials.
Use materials with low dielectric constants and low loss factors to reduce conduction and radiation losses.
10、Avoid Common Mode Problems:
Ensure differential signal transmission to minimise common mode noise.
Use common mode current suppressors (CMC) to reduce common mode currents.
A combination of these methods and techniques can effectively suppress EMI and ensure that the board design achieves the required performance and compliance in terms of EMI. EMC is a critical aspect of electronic product design and should be considered and optimised early in the design process.