In the process of circuit design, grounding is a commonplace issue. The grounding method needs to be based on specific usage scenarios, and there is no universal grounding method. In this article, we will explain the essence of grounding issues, which is worth savoring carefully.

The same hardware circuit may also have differences in grounding methods if the purpose is different. Overall, the purpose of grounding determines the method of grounding. In terms of performance, grounding can be mainly divided into the following four types:

4. Anti static grounding;

3、Purpose of grounding

The main purposes of grounding are divided into three categories: low impedance to ground, stable ground plane, and balanced ground. Next, we will mainly elaborate on these three aspects：
1. low impedance to ground
Low impedance to the ground means minimizing the impedance between the ground plane as much as possible. This impedance needs to be distinguished between low-frequency and high-frequency application scenarios. If we string a large resistance between the signal plane and
the ground plane, as shown in the following figure:

Analysis:
When low-frequency signals flow from the signal plane to the ground plane, a large inductance is equivalent to a wire directly grounded, and the characteristic exhibited at this time is low impedance.
When high-frequency signals flow from the signal plane to the ground plane, the large inductance exhibits a large impedance, and the characteristic exhibited during testing is high impedance.

2. Ground level stability

Ground stability means that the impedance to the ground is sufficient, and the current is easily discharged directly to the ground, while there is almost no voltage drop on the wire. It will be like a vast ocean, where no matter how many rivers converge, there will be no surprises.

3. Ground balance

For power supplies or signals, what is truly valuable to us is often the pressure difference between them. There is a scenario where when a circuit is subjected to external interference, the voltage on both planes increases as a whole (differential mode voltage remains unchanged, common mode voltage increases), as shown in the following figure. In fact, the circuit usually still works normally, and this kind of scenario is often encountered in the production of objects.

An electrostatic pulse is struck onto the circuit board through air, and for local circuits, different distances will inevitably lead to the generation of electrostatic induced pressure differences. At this point, if a metal plate is used to separate it, even if the metal plate is floating, the induced electric
field will be uniform for the circuit board behind the metal plate. Although induced interference still exists, at least the circuit is basically balanced. Of course, it would be better if this metal plate were grounded. Of course, the common mode voltage is generally not maintained because the
impedance of the transmission line is uneven, which often leads to differential mode voltage interference. It is best not to face the issue of ground balance, but when there is no way, such as floating equipment, circuit boards that have to be subjected to static electricity impact must consider
the issue of ground balance when protecting them.

4、Common ground coupling interference

Common ground coupling interference is the core issue in dealing with grounding.

For example, in a theater, there are three halls: Hall a, Hall b, and Hall c, with only one exit. When three halls have three sessions at the same time, the area of Hall C is larger and it can accommodate more people. The exit of spectators inside Hall C will affect the exit of personnel
inside Hall A and Hall B. (Hall a, Hall b, and Hall c are equivalent to three return paths to the ground, and the walkway is equivalent to a common ground impedance)

As an example, in Figure 1, the resistance of the RAB section is the common ground impedance part, and the ground currents Io, Ia, and Id flowing through this section will affect each other in this section; If these three currents differ significantly by 1-2 orders of magnitude, the impact
on each other cannot be ignored, especially when a weak ground current branch is used for quantitative measurement, amplification, or AD conversion circuits; Figure 2 isolates the impact of Id on the other two paths; Figure 3 shows that all three ground currents are isolated separately.

5.Common Base Methods

The basic idea is to ensure the independent connection of safety protection ground, working digital ground, working analog ground, working power ground, lightning surge ground, and shielding ground in the design. Finally, during system debugging, based on the problem to be solved between different regions, that is, according to the purpose of grounding, these ground points are connected in the following ways, including:

Because lightning surges and safe grounding currents are generally much greater than the harm of signal currents to people, it is recommended to connect these two grounding points separately to the ground and connect them at a single point at the true ground, especially for lightning protection grounding.