As electronics applications continue to become more compact and has more and more features in same package (think about modern smart phone or tablet), requires system engineers to use multiple power rails and mixed disciplines of circuit design (mix both analogue and digital parts tightly). A typical tablet will consist of items such as a backlight, touch screen, camera, charging system (USB and Wireless), Bluetooth, Wi-Fi, audio outputs (speaker, headphones), and memory for storing data.
Circuits with analog and digital signals tend to cause declaration of several ground references, often leading to a spaghetti-like result, where ideas are distorted and what appear to be solid solutions turn out to be chaotic failures. In order to put engineering foundations back into complex systems, it is imperative that power and grounding solutions are proactively engineered in a manner that optimizes performance and heat dissipation while reducing EMI radiation and signal to noise interference.
How to ground and power complex circuits article demonstrates how to optimize complex circuits from the point of view of power delivery, improved signal integrity and properly grounded functional blocks to implement the final system. The focus is on understanding circuit needs and pre-planning for the final system, because the result of those two steps is a project that effectively moves from the schematic to the final printed circuit board. Any signal (or power supply) used to drive any circuit must be given a proper path to return to its source so circuit designers must consider the source and grounding schemes.
Understanding current flow and the concept of minimizing current loops leads to the obvious conclusion that the single GND method is ideal and preferred as a PCB design approach because it significantly reduces component count, layer count, and potential radiation. Every trace and block will be provided the shortest return path possible on the PCB. By following this guidance, the system designer will only have to control the PCB design from the perspective of proper trace widths as well as smart placement of components and blocks.
The decision regarding single or multiple planes should always be guided by the visualization of return paths.The the single ground plane approach, in most case it is the best one, as it simplify the PCB layout, it lower ground noise and it lower electromagnetic emission.