Grounding is a wire connection set up to discharge charge or provide a reference potential. There are two purposes of grounding. One is to protect the safety of people and equipment from lightning strikes, leakage, static electricity and other hazards. This type of ground wire is called a protective ground wire and should be connected to the real earth. The second is to ensure the normal operation of the equipment, which is called a working ground wire.
1) Suspended ground
A. The equipment ground wire is electrically insulated from the reference ground and other conductors, that is, the equipment suspended ground;
B. In order to prevent the interference current on the chassis from being directly coupled to the signal circuit, the intentional signal ground is insulated from the chassis, that is, the suspended ground of the unit circuit.
2) Single-point grounding
Single-point grounding provides a common reference point for many circuits connected together. Parallel single-point grounding is the simplest. It does not have the problems of common impedance coupling and low-frequency ground loops, so there is no interference.
3) Multi-point grounding
Multi-point grounding can avoid the problem of single-point grounding at high frequencies. Multi-point grounding must be used in digital circuits and high-frequency large signal circuits. Modules and circuits are connected by many short wires (<0.1λ) to reduce the common mode voltage generated by ground impedance.
4) Hybrid grounding
Hybrid grounding includes the characteristics of both single-point grounding and multi-point grounding. For example, the power supply in the system needs single-point grounding, while the RF part needs multi-point grounding. Hybrid grounding uses reactive devices to make the grounding system present different characteristics at low and high frequencies, which is necessary in broadband sensitive circuits.
Hybrid grounding of electronic equipment generally divides the ground wire of the equipment into two categories: power ground and signal ground. The power ground wires of each part of the equipment are connected to the power bus, and all signal grounds are connected to the signal bus. The two buses are finally aggregated to a common reference ground.
In summary, the grounding of the shielded room should consider hybrid grounding.
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