Many people likely face a common challenge when designing high-frequency microwave PCBs: how to address power supply noise interference on these boards. To address this, our team consulted a professional technician, who explained that by eliminating the conditions under which the interference occurs, power supply noise can be effectively suppressed. The specific solutions are as follows:

1) Pay attention to the through-holes on the board. Through-holes require etching openings in the power plane to allow space for the holes to pass through. If the openings in the power plane are too large, they will inevitably affect the signal circuits, forcing signals to be routed around them, which increases the circuit area and amplifies noise. Additionally, if signal lines are concentrated near these openings and share the same circuit segment, the common impedance will cause crosstalk.

2) Install power supply noise filters. These effectively suppress internal power supply noise, enhancing the system’s immunity to interference and overall reliability. Furthermore, as bidirectional RF filters, they not only remove noise introduced via power lines (preventing interference from other devices) but also filter out self-generated noise (avoiding interference with other devices), thereby suppressing serial-mode common-mode interference.

3) Power isolation transformers. Isolating the power circuit or common-mode ground loop from signal cables can effectively isolate common-mode loop currents generated at high frequencies.

4) Power conditioners. Obtaining a cleaner power supply can significantly reduce power supply noise.

5) Wiring. Power supply input and output lines should not be routed along the edges of circuit boards, as this can easily generate radiation and interfere with other circuits or equipment.

6) Analog and digital power supplies should be separated. High-frequency devices are typically very sensitive to digital noise, so they should be separated and connected at the power supply input. If signals cross between analog and digital sections, a loop can be established at the signal crossover point to minimize the loop area.

7) Avoid overlapping independent power supplies between different layers. Try to stagger them; otherwise, power supply noise can easily couple through parasitic capacitance.

8) Isolate sensitive components. Some components, such as phase-locked loops (PLLs), are highly sensitive to power supply noise. They should be placed as far away from the power supply as possible.

9) Ensure sufficient ground traces for connections. Each signal should have its own dedicated signal loop, and the loop area of the signal and ground traces should be minimized—that is, the signal and ground traces should run parallel to each other.

10) Route power lines. To minimize signal loops, noise can be reduced by routing power lines close to signal lines.

11) To prevent power supply noise on the circuit board from interfering with other devices and to mitigate cumulative noise caused by external interference on the power supply, bypass capacitors can be grounded along the interference path (excluding radiation). This allows noise to be bypassed to ground, thereby preventing interference with other equipment and devices.

Conclusion: Power supply noise is generated directly or indirectly by the power supply and interferes with circuits. When mitigating its impact on circuits, a general principle must be followed: on the one hand, we must strive to prevent power supply noise from affecting the circuit; on the other hand, we should also minimize the impact of external factors or the circuit itself on the power supply to prevent the power supply noise from worsening.