Types of PCB Grounding Explained | PCB Layout

Summary

In this Altium Academy video, host Zach Peterson explores various ground connection types found in component data sheets and schematics. He explains the purpose of different grounds like DGND, AGND, PGND, and SGND, particularly in components with analog inputs. Zach discusses how to reconcile multiple ground connections with the need for a consistent ground potential on a PCB, using net ties and proper layout techniques to prevent noise interference and maintain signal integrity.

Takeaways

• 😀 The video discusses various types of ground connections found in component data sheets and reference designs.
• 🔌 Common ground names include DGND (digital ground), AGND (analog ground), SGND (signal ground), and PGND (power ground or primary/secondary ground depending on the context).
• 🤔 The need for a consistent ground potential is reconciled with different ground connections by understanding their purposes and how they should be connected in a PCB layout.
• 📚 Component data sheets often provide guidance on how to connect different ground pins, such as connecting digital and analog grounds at a single point.
• 💻 In schematics, net ties can be used to connect different ground nets, ensuring that they behave as a single ground in the PCB layout.
• 🛠️ Proper layout and routing are crucial to prevent digital signals from injecting noise into analog inputs, which can affect the accuracy of measurements in components like ADCs and DACs.
• 🔍 For components with isolated DC/DC converters, physically separated grounds are necessary to maintain galvanic isolation, and these should be connected with a safety capacitor, not a net tie.
• 🔗 The placement of net ties is important; they should be located in a way that prevents return currents from passing between different ground regions, ensuring a uniform ground potential.
• 🚫 Avoid splitting the ground plane unless necessary, as it can lead to EMI problems and noise injection into sensitive analog inputs.
• 🔄 For high-frequency signals, the return path is well-defined and closely follows the signal trace, making it less necessary to split the ground plane.
• 🔋 In power converters like buck converters, PGND carries high pulsed currents and should be carefully routed and connected back to GND using a net tie.

Q & A

What is the main topic discussed in the Altium Academy video by Zach Peterson?

The main topic discussed is the different types of ground connections found in component data sheets, reference designs, and schematics, and how to reconcile these with the need for a consistent ground potential in PCB design.

Why might different ground connections like PGND, AGND, DGND, and SGND be used in component data sheets?

Different ground connections are used to denote specific types of grounds such as digital ground (DGND), analog ground (AGND), signal ground (SGND), and power ground (PGND), which may be necessary for components requiring separate analog or digital references or isolation.

What does DGND typically stand for in the context of a component data sheet?

DGND typically stands for Digital Ground, which is a ground connection specifically for digital signals within a component.

How does the meaning of SGND and PGND change when dealing with an isolated switching regulator?

In the case of an isolated switching regulator, SGND and PGND do not mean signal ground and power ground, respectively. Instead, S usually stands for secondary, referring to the secondary side of the package, and P stands for primary, referring to the primary side of the package.

What is the recommended approach for dealing with different ground connections in a PCB layout?

The recommended approach is to use a single ground plane and connect different ground connections at a single point using a net tie to maintain a consistent ground potential across the PCB.

Why is it important to connect digital ground and analog ground at a single point in a schematic?

Connecting digital ground and analog ground at a single point ensures that any digital signals are measured with respect to the same ground reference as the analog signals, preventing ground offset issues that could affect signal measurements.

What is the significance of routing digital signals only in the designated digital ground region (DGND) in a PCB layout?

Routing digital signals only in the DGND region helps to prevent these signals from injecting noise into the analog input, thus maintaining signal integrity and preventing electromagnetic interference (EMI).

How should the net tie between different ground connections be placed in a PCB layout?

The net tie should be placed at a single point where it creates a uniform ground potential across the different ground planes, ideally close to where the ground connections are located on the chip, and avoiding any return current passing between the two regions.

What is the purpose of using a safety capacitor to connect primary and secondary grounds in an isolated DC/DC converter module?

A safety capacitor with high capacitance is used to allow noise on the output side to flow back to the primary ground on the input side while maintaining isolation across the barrier, preventing any direct electrical connection that could compromise safety.

How should PGND be connected back to GND in a buck converter integrated circuit?

PGND should be connected back to GND using a net tie in the PCB layout, ensuring that it is connected in parallel to all output circuitry and making the connection deliberately, either on the top or bottom layer.

What are some common components that might have different ground connections built into their package?

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