Ground Layer in PCB

The ground plane in the PCB is a key component. It is mainly made of copper and covers all areas on the PCB where there are no components or traces, serving as a common return path for current. Here is a detailed explanation of the PCB ground plane:

Definition and function of the ground plane:

The ground plane acts as a common return path for current from various devices in the PCB design, and is often referred to as the 0 potential node. All other voltages in the system are relative to this node.

It helps to reduce the voltage gradient between the chassis and the board, and in the board. The voltage gradient is the main source of common-mode RF fields and the source of RF power from the chassis to the ground.

Design principles of the ground plane:

On the PCB layout, the ground plane should be as complete as possible, and there should be no unconnected parts. If there is an open space on the board, copper and vias should be used to fill the ground plane.

The ground plane is usually placed on the bottom layer, while the traces and components are placed on the top layer, especially when the board has two layers.

The formation of conductive material loops in the ground plane should be avoided, as this will increase the susceptibility of the ground plane to electromagnetic interference (EMI).

Application of ground plane in multilayer PCB:

In multilayer PCB, one or more pairs of voltage and ground planes are usually included. The function of the power plane is equivalent to a low-inductance capacitor that can constrain the RF capacitance generated on components and channels. For multilayer board designs such as 6-layer boards, it is recommended to arrange 2 ground planes to improve performance. This is because the ground layer is usually used as a return path for signals, and multiple ground layers can more effectively manage current return and reduce interference.

Relationship between ground layer and signal layer:

Components should be arranged on the signal layer close to the ground layer so that the return path is short and the traces are coupled to the ground. This helps to reduce interference during signal transmission. In mixed signal (such as analog and digital) circuits, special care should be taken with ground connections. The analog and digital parts should be physically separated, but they still need to be connected to the power return path.

Importance of ground plane in high-speed digital circuits:

In high-speed digital circuits, due to the high clock frequency, the pulse signal contains rich high-frequency components, which will generate a large voltage on the ground line. The interference of ground impedance on digital circuits is considerable, so suppressing or preventing ground interference is one of the most important issues to consider in high-speed digital circuit PCB design.

In summary, the ground layer plays a vital role in PCB design. It not only provides a common return path for current, but also helps to reduce interference and improve circuit performance. When designing PCBs, the layout, design principles and relationship between the ground layer and other layers should be fully considered.