Proper PCB routing is critical for analog and mixed-signal circuits, where noise, coupling, and grounding can directly affect accuracy, stability, and performance. This article summarizes key routing principles and practical methods.

1. Partition the Layout Clearly

Separate analog, digital, and power sections physically.

Place sensitive analog circuits away from high-speed digital traces.

Avoid crossing analog and digital signal paths.

Group related components to shorten critical loops.

2. Ground Design Is the Core

Use single-point grounding or star ground for sensitive analog circuits.

Separate analog ground (AGND) and digital ground (DGND).

Connect AGND and DGND at only one point (near the power supply).

Use wide ground planes to reduce impedance and noise.

3. Power Supply Routing

Use separate power regulators for analog and digital sections.

Place decoupling capacitors close to IC power pins.

Use wide, short traces for power paths.

Avoid shared power paths between analog and digital circuits.

4. Analog Signal Routing

Keep analog traces short, direct, and wide.

Avoid running analog signals parallel to digital signals.

Use guard rings around high-impedance analog nodes.

Maintain consistent impedance for precision analog paths.

5. Digital Signal Routing

Route digital traces away from sensitive analog areas.

Minimize loop area and return path impedance.

Use series termination for high-speed digital signals.

Avoid sharp angles; use 45° or curved traces.

6. Isolation and Shielding

Use ground planes as shielding between analog and digital layers.

Add guard traces connected to ground along critical analog signals.

Maintain proper clearance and creepage distances.

Isolate high-current or high-voltage circuits.

7. Avoid Common Noise Sources

Reduce crosstalk by increasing spacing between traces.

Do not split ground planes under mixed-signal devices.

Avoid running signals over ground plane gaps.

Keep clock lines and switching circuits away from inputs.

8. Thermal and Stability Considerations

Route heat-generating components away from precision analog parts.

Ensure stable temperature for sensors and references.

Use thermal reliefs where necessary.

Conclusion

PCB routing for analog and mixed-signal circuits emphasizes isolation, clean grounding, short paths, and careful separation of analog and digital domains. Following these rules significantly improves noise performance, linearity, and reliability.