PCB Anti-Interference Design: From Theory to Practice, 3 Key Tips for Stable Signals

1. Introduction: Why Does Your PCB Suffer From Interference?

When designing industrial control or high-frequency circuits, many engineers face this problem: the PCB works normally in the lab but experiences signal loss or data errors on-site. This is mostly due to inadequate "anti-interference design." Interference comes from sources like electromagnetic radiation, poor grounding, and power noise, but solutions follow a clear pattern. Today, we’ll share 3 practical anti-interference tips you can apply directly.

2. 3 Practical Anti-Interference Tips

1. Tip 1: "Single-Point Grounding" vs. "Multi-Point Grounding"—Choose the Right One

    

   Grounding is the foundation of anti-interference, but many people confuse the application scenarios of these two methods. For example, using single-point grounding for high-frequency circuits (frequency >10MHz) leads to overly long ground wires, creating parasitic inductance that introduces interference. Using multi-point grounding for low-frequency circuits (frequency <1MHz) forms ground loops, causing noise coupling.

    

   Practice Method: Use "single-point grounding" for low-frequency circuits (e.g., analog sensors), where all ground wires converge to one ground point. Use "multi-point grounding" for high-frequency circuits (e.g., RF modules), keeping ground wire length below 1/20 of the wavelength (e.g., <6mm for 2.4GHz RF circuits) to reduce parasitic inductance.

2. Tip 2: Double Suppression of Power Noise with "Shielding Cans" + "Filter Capacitors"

    

   Power noise is a major interference source—especially switching power supplies, which generate significant high-frequency noise that spreads to core chips via power lines. Many people only add one filter capacitor at the power input, ignoring the importance of "shielding."

    

   Practice Method: Add a metal shielding can around power modules (e.g., DC-DC chips) and ground the can. Meanwhile, parallel two capacitors next to the chip’s power pin: a 100nF ceramic capacitor (filters high-frequency noise) and a 10μF electrolytic capacitor (filters low-frequency noise). Keep the capacitors within 5mm of the chip pin to shorten the current loop.

3. Tip 3: "Differential Routing" Design to Resist External Interference

    

   For differential signals like RS485 and CAN, improper routing makes them vulnerable to external electromagnetic interference, causing communication failures. For example, inconsistent length or uneven spacing of differential pairs breaks signal symmetry, reducing anti-interference ability.

    

   Practice Method: Control the length difference of differential pairs within 5% (e.g., <5mm for 100mm total length). Maintain equal spacing (e.g., 2mm) during routing, avoiding crosses or proximity to other signal lines. Parallel a 100Ω matching resistor at both ends of the differential pair to reduce signal reflection.

3. Conclusion: The Core of Anti-Interference Design—"Reduce Interference at the Source"

Anti-interference is not a "post-fix"; it should be considered early in the design phase. For example, choosing chips with strong anti-interference capabilities during component selection and keeping layouts away from interference sources (e.g., motors, relays) is more effective than adding shielding cans later. It’s recommended to test the waveform of key signals with an oscilloscope after each design to accumulate experience gradually.