Ground and Layout for Board Designers
In circuit theory courses we are taught that ground is a voltage rail with zero potential and that it is the reference point for all of the other voltages in the system. When designing real circuits we find that the "ground" that we learned about doesn't really exist. The "real" ground is a wobbly, noisy, spiky, and sometimes inconsistent signal level that we must learn to respect if we want our circuits to work reliably.
In addition, in complex board layouts with a mixture of analog, digital, and transient inducing components (relays, motors, etc) we learn that ground is not an equal potential level and the ground differential across a circuit board can disrupt the intended operation of the circuit. Board layout, component placement, and definition of a grounding pattern, can make a huge difference in the operation of the circuit.
At very high frequencies (RF), signals act much differently as the properties of the board and the trace dimensions have a greater impact on the signal. Circuits must be designed to take these physical properties into account.
We've gathered up some highly informative articles written by Maxim engineers that will give you the perspective needed to help you design your circuits so that they are reliable and robust in the noisy, spiky, high-frequency, real environments in which they need to operate.
Noise, Decoupling Capacitors, and the Ground Plane
The following note provides some practical information on how noise affects digital signals, why you need more than one capacitor to decouple noise, and tips on designing ground planes for circuits that contain both analog and digital signals and must operate in noisy, spiky environments.
The following short note explains that ground is relative and referenced to its surroundings.
PCB Grounding Techniques for Mixed-Signal Circuit Boards
These in-depth articles cover the intricacies of layout in circuits where both analog, digital, and mixed-signal components reside.
This article covers different ground implementations including the "Mecca" ground and provides information on placing components and running traces to minimize crosstalk.
- Tutorial 5450: Successful PCB Grounding with Mixed-Signal Chips - Follow the Path of Least Impedance
This article explains how to minimize noise in systems consisting of multiple subsystems through careful component layout and attention to grounding.
Power Supply, Ground, and Layout in Radio Frequency Designs
Most RF circuit designers understand that high-frequency circuit board designs require careful attention to layout, placement, and signal paths. This article provides good insight into these intricacies for those coming up to speed in RF design.
For those working with very high frequencies, where the traces must be modeled as transmission lines, these articles provides highly informative overviews and design tips on the subjects of layout, placement, and routing requirements in RF designs.