How to ground and power complex circuits

February 11, 2015 //By Nicholaus Smith
How to ground and power complex circuits
Nicholaus Smith of Integrated Device Technology, Inc. considers  methods for grounding and powering  complex circuits.

As electronics applications continue to become more compact, powerful, and versatile, the final system demands and complexities of mobile and stationary devices also are becoming increasingly sophisticated.  This complexity – which demands wireless and wired interconnectivity of analog and digital circuits -- requires system engineers to use multiple power rails and mixed disciplines of circuit design.  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.  This 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.  By taking the time during the design stage to consider each block of a complex system from the current path and noise susceptibility point of view, then placing blocks and powering circuits based on the simple axiom that current always flows in a loop, the complexity faced by today's system engineers can be broken down into manageable pieces, and implemented into a final, robust design.

To demonstrate the theory, let’s examine a simple circuit and consider the shown connections.  This basic circuit consists of three elements, a low-drop out (LDO) linear regulator, a micro-processing USB data-to-audio driver, and a speaker.  All are powered by a USB plug connected to some computing host.  In this example, the USB-to-audio driver must be powered by 3.3V.  Since

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