In PCB design, a well-designed circuit can still produce noise during testing, leading to performance issues or even requiring a board redesign. Below, we explore strategies to reduce circuit board noise effectively.

Functional Module Separation

A high-performance board will often have a clear layout of functional modules. A functional module is a collection of circuits and components dedicated to a specific function. For noise reduction:

• Group components by function: Position related components close together to minimize wiring length.
• Use Faraday cages for shielding: Separate and shield sensitive modules, as seen in devices like mobile phones. Shielded modules help maintain signal integrity and prevent high-frequency interference.

Analog and Digital Circuit Separation

When analog and digital circuits are on the same PCB, separate them physically to prevent interference.

• Quiet Zone Design: Designate “quiet zones” between analog, digital, or other modules to isolate them. Quiet zones aren’t connected to the PCB ground. However, if space is limited:
  • Use transformers or isolating components (e.g., CMOS or crystal transistors) for signal isolation.
  • Use filtering circuits to eliminate noise before the signal enters the module, which also helps with ESD protection.
  • Common-mode inductors stabilize signals and reduce interference, especially high-frequency noise.

Trench Protection Technology

Trench protection removes copper foil in isolation zones to expose the PCB material, forming a “trench” around modules. This method:

• Provides resilience to peak voltage impacts and helps with discharge protection, reducing circuit board noise.
• Introduces a bridge concept where power, ground, and signal traces connect each section. Bridges can limit RF loop currents that degrade PCB performance.

Handling AGND and DGND in ADC and DAC Devices

Many analog-to-digital (ADC) or digital-to-analog (DAC) components have internal connections between analog and digital grounds (AGND and DGND). These devices should have:

• A dedicated reference ground to prevent digital current from flowing back improperly, reducing noise and EMI.
• Segmentation to ensure minimal ground interference.

Summary

Segment circuits into modules with quiet zones between them to reduce power and ground noise, minimizing interference and noise on the PCB circuit board.