Source: Electricity Forum
01 Grounding method
Grounding can be divided into four categories: floating, single-point grounding, multi-point grounding, and hybrid grounding.
1. Floating
(1) Purpose: To isolate the circuit or equipment from the common wire that may cause circulation from the common ground wire, and to float the ground to make it easy to cooperate with circuits of different potentials.
(2) Disadvantages: It is easy to accumulate static electricity and cause strong electrostatic discharge.
(3) Compromise: access to the bleeder resistor.
2. Single-point grounding
(1) Method: Only one physical point in the line is defined as the grounding reference point, and all grounding needs to be connected to it.
(2) Disadvantages: not suitable for high-frequency occasions.
3. Multi-point grounding
(1) Method: All points that need to be grounded are directly connected to the nearest grounding plane, so as to make the length of the grounding wire the shortest.
(2) Disadvantages: maintenance is more troublesome.
4. Mixed grounding
Method: Single-point and multi-point grounding are selected as needed.
The large-area copper grounding in the PCB is actually multi-point grounding, so the single-sided PCB can also achieve multi-point grounding. Most of the multilayer PCBs are high-speed circuits, and the increase of the formation layer can effectively improve the electromagnetic compatibility of the PCB, which is the basic means to improve the signal anti-interference.
02 Detailed description & suggestions of common grounding lines
1. Single-point grounding
Single-point grounding considerations:
(1) Do not use it in a system with a mixture of high-power and low-power circuits, because the ground current in the high-power circuit will affect the normal operation of the low-power circuit.
(2) The most sensitive circuit should be placed at point A, which is the most stable. The way to solve the disadvantages of single-point grounding is to connect single-point grounding in parallel. However, a single point grounding in parallel requires more wires, and in practice, a series or parallel hybrid grounding can be used.
2. Series single-point, parallel single-point mixed grounding
Notes:
(1) The circuits are grouped according to their characteristics, and the circuits that are not prone to interference with each other are placed in the same group, and the circuits that are prone to interference with each other are placed in different groups.
(2) A series single-point grounding is used in each group to obtain the simplest ground structure; The grounding of different groups adopts parallel single-point grounding to avoid interference with each other.
The key to this approach is to never share a ground wire with circuits that vary greatly in power or at very different noise levels. These different places can only be connected by one point.
3. Multi-point grounding
Notes:
(1) In order to reduce the inductance of the ground wire, multi-point grounding is often used in high-frequency circuits and digital circuits.
In a multi-point grounding system, each circuit is connected to a low-impedance ground surface, such as a chassis. The ground wire of the circuit should be as short as possible to reduce the inductance. In high-frequency systems, the ground wire is usually controlled within a few millimeters.
(2) It is easy to produce common impedance coupling problems when multi-point grounding.
In low-frequency situations, this problem can be solved by a single point of grounding. However, at high frequencies, this can only be solved by reducing the ground impedance (reducing the common impedance). Due to the skin effect, the current flows only on the surface of the conductor, so increasing the thickness of the conductor does not reduce the resistance of the conductor. Silver-plating on the surface of the conductor reduces the resistance of the conductor. (3) Usually when it is less than 1MHz, it can be grounded at a single point; When it is above 10MHz, it can be grounded at multiple points, and when it is between 1MHz and 10MHz, if the longest grounding wire does not exceed 1/20 of the wavelength, it can be grounded at a single point, otherwise it can be grounded with multiple points.
4. Mixed grounding
Notes:
(1) The capacity of the ground capacitor is generally less than 10nF, depending on the frequency that needs to be grounded.
(2) If the equipment is safely disconnected, the ground loop will be cut off, and the ground loop current interference can be solved. However, for safety reasons, the chassis must be connected to a safe ground. The grounding system shown in the diagram above solves this problem, and for the higher frequency ground loop current, the ground wire is disconnected; And for 50Hz AC, the chassis is reliably grounded.
03 Epilogue
The above details of the relevant grounding treatment, I believe it can give you some help!