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PCB Tech

PCB Tech

PCB design of multi-layer PCB grounding method
2021-08-11
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Author:ipcb

PCB design of multi-layer PCB grounding method, In high-density and high-frequency applications, four-layer boards are usually used, which is more than 20DB better than two-layer boards in terms of electromagnetic compatibility (EMC). Under the condition of a four-layer board, a complete ground plane and a complete power plane can often be used. Under this condition, only several groups of circuit ground wires are connected to the ground plane, and operating noise is specially treated.


There are many ways to connect the ground wire of each circuit to the ground plane, including:

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Figure: PCB design: multi-layer PCB board grounding method

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Figure: PCB design _ multi-layer PCB board grounding method (2)


1. Single-point grounding: The ground wires of all circuits are connected to the same point on the ground plane, which is divided into series single-point grounding and parallel single-point grounding.


2. Multi-point grounding: The ground wires of all circuits are grounded nearby, and the ground wires are short and suitable for high-frequency grounding.


3. Mixed grounding: mix single-point grounding and multi-point grounding.


    Between low frequency, low power and the same power layer, single-point grounding is the most suitable, usually used in analog circuits; generally star-shaped connection is used to reduce the influence of possible series impedance. High-frequency digital circuits need to be grounded in parallel. Generally, it is relatively simple to deal with through ground holes; generally, all modules will use two grounding methods, and the circuit ground wire and the ground plane are connected by a hybrid grounding method.


Grounding method of multi-layer PCB board (two)


    If you do not choose to use the entire plane as a common ground wire, for example, when the module itself has two ground wires, you need to divide the ground plane, which often interacts with the power plane.


Pay attention to the following principles when grounding:


(1) Align the various planes to avoid the overlap between the unrelated power plane and the ground plane, otherwise it will cause all the ground planes to fail and interfere with each other;


(2) In the case of high frequency, there will be coupling between layers through the parasitic capacitance of the circuit board;


(3) The signal lines between the ground planes (such as the digital ground plane and the analog ground plane) are connected by a ground bridge, and the nearest return path is configured through the nearest through hole.


(4) Avoid running high-frequency traces such as clock lines near the isolated ground plane, which may cause unnecessary radiation.


(5) The area of the loop formed by the signal line and its loop is as small as possible, which is also called the minimum loop rule; the smaller the loop area, the less external radiation, and the less interference from the outside world. When dividing the ground plane and signal routing, consider the distribution of the ground plane and important signal traces to prevent problems caused by slotting in the ground plane.


The above is the grounding method of multi-layer PCB board in PCB design. It briefly introduces the grounding method of multi-layer PCB board and several principles to pay attention to from two major aspects.