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Successful PCB Grounding with Mixed-Signal Components

Proper grounding is one of the most critical aspects of PCB layout, and commonly raises questions among PCB design newcomers and veterans alike. This is particularly true for designs incorporating so-called “mixed-signal” components that handle both analog and digital signals. At Bittele Electronics, we have seen a wide variety of grounding strategies during our years of experience in providing PCB Fabrication and PCB Assembly services. This article is written from Bittele’s perspective on this topic; we will highlight the most common and well-established strategies for mixed-signal grounding, and discuss the effects of these strategies on the PCB Production Process.

Bypass Capacitors

Bypass capacitors are absolutely essential for any IC that handles digital signals; they act to supply current to the pins of the IC during high speed switching operations in order to suppress transients that can cause instability in the main power supply. It is common knowledge that bypass capacitors should be placed as close as possible to the pins of the IC in order to minimize impedance of the return path, but it is important not to get carried away with this guideline. Of course, the placement of your bypass capacitors must fall within Bittele’s Part-to-Part Spacing requirements, but beyond that there comes a point of diminishing returns. Very rarely is there any need to shrink your bypass capacitors down to 0201 Packages just to squeeze them in as close as possible to your IC, and specifying these tiny components for all of your designs will needlessly drive up the cost of PCB Assembly since they are not included in Bittele’s Standard Cost PCB Options.

Separate Ground Planes

Familiar with the idea that transients from high-speed digital signals can disrupt the integrity of analog ground, some designers choose to separate the return paths for analog and digital signals onto two entirely separate ground planes. This is certainly a viable strategy, but it should be noted that the cost and lead time of PCB Fabrication will increase significantly with the number of copper layers specified in your PCB Stackup.

Cutting the Ground Plane

Many tutorials recommend placing a conceptual “cut” in the ground plane layer of your PCB in order to separate digital and analog return paths. This option is much more economical in terms of the PCB Fabrication process, allowing for an altogether lower number of copper layers in the design. This grounding strategy can be more complicated to plan out than completely separate ground planes, but it can win you some savings in terms of project cost and lead time in the long run.

If you find yourself with any further questions about mixed-signal grounding in your PCB projects with Bittele, or to send along your PCB Design Files for an official quote today, you can Contact Us any time. We can be reached via email at sales@7pcb.com, or toll free at 1-888-812-1949.

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