The methods to reduce interference on a PCB board are:
1. Minimize the area of the differential mode signal loop.
2. Reduce high-frequency noise return (via filtering, isolation, and impedance matching).
3. Lower the common mode voltage (through proper grounding design).
### 47 Principles of High-Speed PCB EMC Design
**II. Summary of PCB Design Principles**
**Principle 1:** If the PCB clock frequency exceeds 5 MHz or the signal rise time is less than 5 ns, a multi-layer board design is generally required.
**Reason:** A multi-layer board design effectively controls the signal loop area.
**Principle 2:** In multi-layer boards, key signal layers (such as those containing clock lines, buses, interface signals, RF lines, reset lines, chip select lines, and various control signals) should be placed adjacent to a complete ground plane, preferably between two ground planes.
**Reason:** Key signal lines often carry strong radiation or highly sensitive signals. Positioning them close to a ground plane reduces the signal loop area, minimizes radiation intensity, and enhances immunity to interference.
**Principle 3:** In single-layer boards, both sides of key signal lines should be covered with ground.
**Reason:** Grounding both sides of key signals reduces the signal loop area and prevents crosstalk between signal lines.
**Principle 4:** In double-layer boards, large ground areas should be placed under the key signal lines, similar to a single-sided board layout.
**Reason:** This is analogous to the design for multi-layer boards, where key signals are placed close to the ground plane.
**Principle 5:** In multi-layer boards, the power plane should be offset by 5H-20H from its adjacent ground plane (where H is the distance between the power and ground planes).
**Reason:** Offsetting the power plane relative to the return ground plane helps suppress edge radiation.
**Principle 6:** The wiring layer’s projection should align with the reflow plane layer’s area.
**Reason:** Misalignment between the wiring layer and the reflow plane can lead to edge radiation and an increased signal loop area, resulting in higher differential mode radiation.
**Principle 7:** In multi-layer boards, it is recommended that the TOP and BOTTOM layers not carry signals above 50 MHz.
**Reason:** High-frequency signals should ideally be routed between the two plane layers to minimize radiation into the surrounding space.
Principle 8: For a single-board design with an operating frequency above 50MHz, if the second layer and the penultimate layer are signal routing layers, the TOP and BOTTOM layers should be covered with grounded copper planes.
Reason: It is ideal to route high-frequency signals between the two plane layers to minimize radiation into the surrounding space.
Principle 9: In a multilayer PCB, the primary power plane (the most commonly used power plane) should be placed close to the ground plane.
Reason: The proximity of the power and ground planes helps reduce the loop area of the power circuit, thereby improving performance.
Principle 10: In a single-layer PCB, a ground trace must be placed next to and parallel to the power trace.
Reason: This helps minimize the area of the current loop for the power supply, reducing noise and improving signal integrity.
Principle 11: In a double-layer PCB, a ground trace must be placed next to and parallel to the power trace.
Reason: This minimizes the area of the power supply current loop, which helps reduce noise and maintain signal quality.
Principle 12: When designing layer stacks, avoid placing adjacent signal routing layers whenever possible. If adjacent routing layers are unavoidable, the spacing between the layers should be increased, while the distance between a signal layer and its ground or power plane should be minimized.
Reason: Parallel signal traces on adjacent layers can lead to crosstalk, which affects signal integrity.
Principle 13: Adjacent plane layers should not have overlapping projection areas.
Reason: Overlapping projection areas increase the coupling capacitance between planes, which can cause noise to couple between layers.
Principle 14: When designing the PCB layout, always aim to align components in the direction of signal flow and avoid creating long, looping traces.
Reason: Minimizing loops helps prevent direct signal coupling, which can degrade signal quality.
Principle 15: When multiple modules are placed on the same PCB, digital circuits, analog circuits, and high-speed circuits should be laid out in separate areas.
Reason: This reduces the risk of interference between digital, analog, high-speed, and low-speed circuits.
Principle 16: When a PCB contains circuits with high, medium, and low-speed signals, high-speed and medium-speed circuits should be routed away from the interface.
Reason: This prevents high-frequency noise from the circuits from radiating through the interface and affecting other parts of the design.
Principle 17: Energy storage and high-frequency filter capacitors should be placed close to the unit circuits or devices with significant current changes (e.g., power supply modules, input/output terminals, fans, and relays).
Reason: Placing capacitors near high-current devices reduces the loop area of the current path, improving overall performance.
Principle 18: The power input filter circuit on the PCB should be located near the interface.
Reason: This placement ensures that the filtered signal is not re-coupled with noise or unwanted signals after filtering.
Principle 19: Filtering, protection, and isolation components for the interface circuit should be placed as close to the interface as possible.
Reason: This ensures optimal protection, filtering, and isolation for the circuit.
Principle 20: If both filter and protection circuits are used at the interface, the protection circuit should be placed first, followed by the filter.
Reason: The protection circuit suppresses external overvoltage and overcurrent. Placing the filter before the protection circuit may damage the filter with high voltage or current spikes.
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1. Minimize the area of the differential mode signal loop.
2. Reduce high-frequency noise return (via filtering, isolation, and impedance matching).
3. Lower the common mode voltage (through proper grounding design).
### 47 Principles of High-Speed PCB EMC Design
**II. Summary of PCB Design Principles**
**Principle 1:** If the PCB clock frequency exceeds 5 MHz or the signal rise time is less than 5 ns, a multi-layer board design is generally required.
**Reason:** A multi-layer board design effectively controls the signal loop area.
**Principle 2:** In multi-layer boards, key signal layers (such as those containing clock lines, buses, interface signals, RF lines, reset lines, chip select lines, and various control signals) should be placed adjacent to a complete ground plane, preferably between two ground planes.
**Reason:** Key signal lines often carry strong radiation or highly sensitive signals. Positioning them close to a ground plane reduces the signal loop area, minimizes radiation intensity, and enhances immunity to interference.
**Principle 3:** In single-layer boards, both sides of key signal lines should be covered with ground.
**Reason:** Grounding both sides of key signals reduces the signal loop area and prevents crosstalk between signal lines.
**Principle 4:** In double-layer boards, large ground areas should be placed under the key signal lines, similar to a single-sided board layout.
**Reason:** This is analogous to the design for multi-layer boards, where key signals are placed close to the ground plane.
**Principle 5:** In multi-layer boards, the power plane should be offset by 5H-20H from its adjacent ground plane (where H is the distance between the power and ground planes).
**Reason:** Offsetting the power plane relative to the return ground plane helps suppress edge radiation.
**Principle 6:** The wiring layer’s projection should align with the reflow plane layer’s area.
**Reason:** Misalignment between the wiring layer and the reflow plane can lead to edge radiation and an increased signal loop area, resulting in higher differential mode radiation.
**Principle 7:** In multi-layer boards, it is recommended that the TOP and BOTTOM layers not carry signals above 50 MHz.
**Reason:** High-frequency signals should ideally be routed between the two plane layers to minimize radiation into the surrounding space.
Principle 8: For a single-board design with an operating frequency above 50MHz, if the second layer and the penultimate layer are signal routing layers, the TOP and BOTTOM layers should be covered with grounded copper planes.
Reason: It is ideal to route high-frequency signals between the two plane layers to minimize radiation into the surrounding space.
Principle 9: In a multilayer PCB, the primary power plane (the most commonly used power plane) should be placed close to the ground plane.
Reason: The proximity of the power and ground planes helps reduce the loop area of the power circuit, thereby improving performance.
Principle 10: In a single-layer PCB, a ground trace must be placed next to and parallel to the power trace.
Reason: This helps minimize the area of the current loop for the power supply, reducing noise and improving signal integrity.
Principle 11: In a double-layer PCB, a ground trace must be placed next to and parallel to the power trace.
Reason: This minimizes the area of the power supply current loop, which helps reduce noise and maintain signal quality.
Principle 12: When designing layer stacks, avoid placing adjacent signal routing layers whenever possible. If adjacent routing layers are unavoidable, the spacing between the layers should be increased, while the distance between a signal layer and its ground or power plane should be minimized.
Reason: Parallel signal traces on adjacent layers can lead to crosstalk, which affects signal integrity.
Principle 13: Adjacent plane layers should not have overlapping projection areas.
Reason: Overlapping projection areas increase the coupling capacitance between planes, which can cause noise to couple between layers.
Principle 14: When designing the PCB layout, always aim to align components in the direction of signal flow and avoid creating long, looping traces.
Reason: Minimizing loops helps prevent direct signal coupling, which can degrade signal quality.
Principle 15: When multiple modules are placed on the same PCB, digital circuits, analog circuits, and high-speed circuits should be laid out in separate areas.
Reason: This reduces the risk of interference between digital, analog, high-speed, and low-speed circuits.
Principle 16: When a PCB contains circuits with high, medium, and low-speed signals, high-speed and medium-speed circuits should be routed away from the interface.
Reason: This prevents high-frequency noise from the circuits from radiating through the interface and affecting other parts of the design.
Principle 17: Energy storage and high-frequency filter capacitors should be placed close to the unit circuits or devices with significant current changes (e.g., power supply modules, input/output terminals, fans, and relays).
Reason: Placing capacitors near high-current devices reduces the loop area of the current path, improving overall performance.
Principle 18: The power input filter circuit on the PCB should be located near the interface.
Reason: This placement ensures that the filtered signal is not re-coupled with noise or unwanted signals after filtering.
Principle 19: Filtering, protection, and isolation components for the interface circuit should be placed as close to the interface as possible.
Reason: This ensures optimal protection, filtering, and isolation for the circuit.
Principle 20: If both filter and protection circuits are used at the interface, the protection circuit should be placed first, followed by the filter.
Reason: The protection circuit suppresses external overvoltage and overcurrent. Placing the filter before the protection circuit may damage the filter with high voltage or current spikes.
If you have any PCB manufacturing needs, please do not hesitate to contact me.Contact me
