Power supply noise is a common source of problems in mixed-signal PCB designs. Even when the schematic is correct, poor power distribution and layout can introduce switching noise into analog, RF, or sensor circuits, leading to unstable measurements, reduced signal integrity, or unexpected system behavior.
Here’s a basic power supply block diagram showing input, output, and return path. A clean, low-impedance return path is critical for minimizing noise:
I wanted to start a discussion on the layout practices designers use to deliver clean power to noise-sensitive circuits.
A clean power supply isn’t just about choosing the right regulator. PCB layout plays an equally important role.
Some common sources of power-related noise include:
- Switching regulators
- High-current return paths
- Shared power and ground impedance
- Poor decoupling capacitor placement
- Long or narrow power traces
The goal is to isolate noisy circuits and provide a low-impedance power path to sensitive components.
From a layout perspective, a few practices can significantly reduce power-supply noise:
- Place decoupling capacitors as close as possible to the IC power pins.
- Keep power and return-current paths short and direct.
- Separate noisy switching circuits from sensitive analog or RF sections.
- Use solid ground planes to provide a continuous return path.
- Route high-current power traces away from low-level analog signals.
- Use power filters only where isolation between power domains is required.
Good component placement often has a greater impact than adding more filtering later in the design.
Another area that’s often overlooked is planning the power distribution network (PDN) early in the layout.
Before routing, it helps to define:
- Which circuits require isolated power domains
- Current requirements for each rail
- Decoupling strategy for different frequency ranges
- Grounding approach for analog, digital, and RF sections
- Placement of regulators relative to the loads they supply
Reviewing the PDN before routing begins makes it easier to control noise and avoid costly redesigns.
For a deeper look at power supply design, decoupling, grounding, filtering, and PCB layout techniques for sensitive circuits, check out our article: How to Design Power Supply for Sensitive Circuits.
