1. Printed circuit boards (PCBs) are an integral component of electronic equipment.
2. With the widespread adoption of electronic technology and the advancement of integrated circuit technology, various issues related to electromagnetic interference (EMI) have arisen, leading to increased economic losses.
3. Consequently, ensuring electromagnetic compatibility (EMC) has become increasingly crucial.
4. This article aims to analyze the sources of electromagnetic interference in PCBs and explore methods to mitigate them.
Electromagnetic interference in PCB boards can be categorized into two main types. One originates internally within the PCB, primarily due to signal crosstalk along transmission paths caused by parasitic coupling between adjacent circuits and field coupling among internal components. For instance, capacitors on PCBs, particularly those used in high-frequency applications, behave akin to LCR circuits. In practical circuit operation, capacitors exhibit both capacitive and inductive characteristics, with impedance increasing as frequency rises, especially beyond their self-resonant frequency.
Another type of electromagnetic interference arises externally from the PCB. This external interference is subdivided into two types: radiation interference and susceptibility issues. Radiation mainly emanates from harmonic sources like clocks and periodic signals. Additionally, electronic equipment or instruments may introduce second harmonics due to voltage and power fluctuations.
To mitigate PCB electromagnetic interference effectively, attention should focus on the following key points:
1. **Optimized Schematic Design**: Begin with a well-constructed schematic diagram using software such as Altium Designer. All components should ideally be selected from the schematic library, with the option to create custom components if necessary. After drawing the schematic, perform automated checks to detect any errors. Once the schematic is finalized, proceed to PCB layout design. Automated routing results often require manual refinement to ensure optimal layout. Designing for electromagnetic compatibility (EMC) is crucial during PCB layout to minimize potential interference issues.
2. **Selection of Capacitors**: Choose capacitors with minimal equivalent inductance and resistance. Crosstalk, which results from energy coupling between wires, should be managed carefully. According to Faraday’s law of electromagnetic induction, current flowing through a wire generates a magnetic field around it. Interaction between magnetic fields of different wires contributes to crosstalk, primarily influenced by mutual inductance proportional to the current through the wire.
These strategies help in addressing and mitigating electromagnetic interference in PCB designs, ensuring enhanced performance and reliability of electronic systems.
3. Limit the periodic signal to a small area as much as possible. Mutual capacitance, another mechanism that causes crosstalk, occurs when two electrodes couple through an electric field. The solution is to confine the periodic signal to a minimal area and block parasitic coupling paths with external surroundings. When necessary, filters can be employed to mitigate external sensitivities such as radio frequency interference and electrostatic discharge.
4. Anti-interference methods in PCB design:
(1) Selection of PCB board materials: Printed circuit boards are categorized into single-sided, double-sided, and multilayer boards. Epoxy glass cloth is commonly used as a substrate material due to its advantages: it minimizes expansion, reducing the loop area and differential mode interference; it exhibits low water absorption, high heat resistance, chemical corrosion resistance, and impact resistance.
(2) PCB board wiring: When wiring, adhere to the principle of flux cancellation. This principle ensures that magnetic lines of force generated by transmission lines and return paths cancel each other out, thereby nullifying electric flux. For single-sided boards lacking a ground plane, focus on minimizing the loop area of power and signal paths. Use protective grounding by running ground wires close to power and signal wires and routing them together. High-speed signal routes should avoid acute or right-angle bends, favoring straight or obtuse angles.
(3) PCB board layout: PCB design software typically includes automated layout functions, but manual adjustment is often necessary to meet specific requirements. Separate digital and analog circuit sections with adequate space in between. Segment the layout into high-speed, medium-speed, low-speed, and I/O circuit partitions to minimize interference from high-speed circuits on other sections.
Conclusion: Designing printed circuit boards entails careful consideration of numerous factors. Neglecting electromagnetic compatibility concerns during design can significantly impact circuit board performance. Therefore, thorough consideration of wiring, layout, grounding, shielding, and other factors is crucial to prevent signal crosstalk on PCBs.
2. With the widespread adoption of electronic technology and the advancement of integrated circuit technology, various issues related to electromagnetic interference (EMI) have arisen, leading to increased economic losses.
3. Consequently, ensuring electromagnetic compatibility (EMC) has become increasingly crucial.
4. This article aims to analyze the sources of electromagnetic interference in PCBs and explore methods to mitigate them.
Electromagnetic interference in PCB boards can be categorized into two main types. One originates internally within the PCB, primarily due to signal crosstalk along transmission paths caused by parasitic coupling between adjacent circuits and field coupling among internal components. For instance, capacitors on PCBs, particularly those used in high-frequency applications, behave akin to LCR circuits. In practical circuit operation, capacitors exhibit both capacitive and inductive characteristics, with impedance increasing as frequency rises, especially beyond their self-resonant frequency.
Another type of electromagnetic interference arises externally from the PCB. This external interference is subdivided into two types: radiation interference and susceptibility issues. Radiation mainly emanates from harmonic sources like clocks and periodic signals. Additionally, electronic equipment or instruments may introduce second harmonics due to voltage and power fluctuations.
To mitigate PCB electromagnetic interference effectively, attention should focus on the following key points:
1. **Optimized Schematic Design**: Begin with a well-constructed schematic diagram using software such as Altium Designer. All components should ideally be selected from the schematic library, with the option to create custom components if necessary. After drawing the schematic, perform automated checks to detect any errors. Once the schematic is finalized, proceed to PCB layout design. Automated routing results often require manual refinement to ensure optimal layout. Designing for electromagnetic compatibility (EMC) is crucial during PCB layout to minimize potential interference issues.
2. **Selection of Capacitors**: Choose capacitors with minimal equivalent inductance and resistance. Crosstalk, which results from energy coupling between wires, should be managed carefully. According to Faraday’s law of electromagnetic induction, current flowing through a wire generates a magnetic field around it. Interaction between magnetic fields of different wires contributes to crosstalk, primarily influenced by mutual inductance proportional to the current through the wire.
These strategies help in addressing and mitigating electromagnetic interference in PCB designs, ensuring enhanced performance and reliability of electronic systems.
3. Limit the periodic signal to a small area as much as possible. Mutual capacitance, another mechanism that causes crosstalk, occurs when two electrodes couple through an electric field. The solution is to confine the periodic signal to a minimal area and block parasitic coupling paths with external surroundings. When necessary, filters can be employed to mitigate external sensitivities such as radio frequency interference and electrostatic discharge.
4. Anti-interference methods in PCB design:
(1) Selection of PCB board materials: Printed circuit boards are categorized into single-sided, double-sided, and multilayer boards. Epoxy glass cloth is commonly used as a substrate material due to its advantages: it minimizes expansion, reducing the loop area and differential mode interference; it exhibits low water absorption, high heat resistance, chemical corrosion resistance, and impact resistance.
(2) PCB board wiring: When wiring, adhere to the principle of flux cancellation. This principle ensures that magnetic lines of force generated by transmission lines and return paths cancel each other out, thereby nullifying electric flux. For single-sided boards lacking a ground plane, focus on minimizing the loop area of power and signal paths. Use protective grounding by running ground wires close to power and signal wires and routing them together. High-speed signal routes should avoid acute or right-angle bends, favoring straight or obtuse angles.
(3) PCB board layout: PCB design software typically includes automated layout functions, but manual adjustment is often necessary to meet specific requirements. Separate digital and analog circuit sections with adequate space in between. Segment the layout into high-speed, medium-speed, low-speed, and I/O circuit partitions to minimize interference from high-speed circuits on other sections.
Conclusion: Designing printed circuit boards entails careful consideration of numerous factors. Neglecting electromagnetic compatibility concerns during design can significantly impact circuit board performance. Therefore, thorough consideration of wiring, layout, grounding, shielding, and other factors is crucial to prevent signal crosstalk on PCBs.
