Ⅰ. What are ground wires?

In an electrical system or electronic equipment, the ground wire is a wire that connects to the ground, the casing, or the reference potential zero. The ground wire is connected to the outer casing in most electrical appliances to prevent electric shock accidents caused by the destruction of the outer casing's inner insulation. For a grounding device, the ground cable is too short. Working ground and safety ground are two types of ground wire. A type of safety grounding wire is used to prevent electric shock accidents when people use electronic equipment such as home appliances and office equipment.

Ⅱ. Types and functions of ground wires

1. Analog ground  wire AGND

The analog ground wire AGND is mostly used in analog circuit parts such as the analog sensor's ADC acquisition circuit, the operational amplification ratio circuit, and so on. 

Because the signal in these analog circuits is analog and weak, it is easily affected by the huge current in other circuits. If the huge current is not distinguished, it will create a large voltage drop in the analog circuit, distorting the analog signal and, in extreme situations, causing the analog circuit to fail.

2. Digital ground  wire DGND 

The digital ground wire DGND.  which is obviously different from the analog ground wire AGND, is primarily used in the digital circuit part, such as the button detection circuit, USB communication circuit, single-chip circuit, and so on. The reason for this is that digital circuits all have the same feature: they are all discrete open light signals with only the digital "0" and "1" distinguishable.

(Digital signal) The voltage changes when leaping from a digital "0" voltage to a digital "1" voltage, or when jumping from a digital "1" voltage to a digital "0" value. The change, according to Maxwell's electromagnetic theory, Around the current, a magnetic field will be produced, causing EMC  radiation to nearby circuits.

No way, a separate digital ground wire DGND  must be used to effectively isolate other circuits in order to limit the circuit's EMC  radiation effect.

3. Power ground  wire PGND 

A low-power circuit is either the analog ground wire AGND or the digital ground wire DGND,  A distinct reference ground wire, known as the power ground wire PGND.  is used in high-power circuits such as motor drive circuits, solenoid valve drive circuits, and so on.

High-power circuits are those that have relatively large currents, as the name implies. A significant current, of course, can easily result in ground offset across separate functional circuits.

(This is known as the Earth Offset Phenomenon.)

When a circuit has a ground offset, the initial 5V voltage may become 4V instead of 5V.

Because the 5V voltage relates to the 0V voltage on the GND ground wire, if the ground offset causes the GND ground wire to rise from 0V to 1V, the prior 5V (5V-0V=5V) voltage becomes the present 4V (5V-1V=4V) voltage.

4. Power ground GND 

The DC ground GND includes the analog ground AGND, the digital ground DGND, and the power ground PGND, the 0V reference ground wire for the entire circuit is made up of all of these different sorts of ground wires. The power ground wire GND  is the name given to this ground line.

All circuits get their energy from the power supply. The power supply provides the voltage and current required for all circuit operations. As a result, the power supply's ground line GND  serves as the 0V voltage reference point for all circuits.

This is why other ground wires, such as an analog ground wire AGND, a digital ground wire DGND.  or a power ground wire PGND, must eventually be connected to the power ground wire GND, 

5. AC ground wire CGND 

The ground wire in an AC system CGND is commonly seen in circuit projects that use AC power, such as AC-DC power supply circuits.

There are two elements to the AC -DC power circuit. The circuit's front stage is the AC component, and the circuit's backstage is the DC component, which is forced to produce two ground wires, one for the AC and one for the DC, 

The AC ground wire serves as the AC  circuit part's 0V reference point, while the DC ground wire serves as the DC circuit part's 0V reference point. Engineers usually use a coupling capacitor or inductor to connect the   AC  ground wire to the DC ground wire in order to unify the ground wire GND in the circuit.

6. Earth ground wire  EGND 

The human body's safe voltage is less than 36 volts. The human body will be damaged if a voltage greater than 36 volts is applied to it. Engineers in the development and design of circuit projects have a shared sense of safety.

Engineers commonly employ the ground wire  EGND in high-voltage and high-current projects, such as household appliances, electric fans, refrigerators, televisions, and other circuits, to improve the circuit's safety factor.

(socket with EGND protection function for earth ground wire)

Why are there three terminals on a household appliance's socket? Only two wires are required for 220V AC: live and neutral. So, why are there three terminals on the sockets?

The socket's three terminals, two of which are the live and neutral wires for 220V, and one of which is the earth ground wire EGND for protection.

It's vital to note that the earth ground wire EGND, which is simply connected to our earth, serves as a high-voltage protection wire, does not participate in the project circuit function, and has no bearing on it.

As a result, the earth ground wire EGND and other types of ground wires GND have quite different circuit meanings.

Ⅲ. The meaning of subdividing the GND ground wire

Engineers may wonder how there can be so many differences between a ground wire  GND and how a basic circuit problem can be so difficult. Why do you need to introduce so many  GND ground functions that are subdivided?

Engineers commonly refer to this type of GND ground wire as GND and do not differentiate it in the schematic design process, making it difficult to distinguish between the GND ground wires of different circuit functions during PCB wiring. All GND ground wires should be connected together.

While this is easy to do, it leads to a number of problems:

Problem 1: Signal Crosstalk

If the ground wires GND of separate functions are connected directly, the high-power circuit will flow through the ground wire GND. A  ffecting the low-power circuit's 0V reference point GND. Resulting in crosstalk between circuit signals.

Problem 2: Signal Accuracy

The correctness of the signal is the primary criterion for evaluating analog circuits. Analog circuits lose their original functional purpose when they are not precise.

Because the  AC power supply's ground wire CGND  is a sine wave, it varies up and down on a regular basis, and its voltage fluctuates as well, not always remaining at 0V like the DC  ground wire GND, 

Connect the ground wires GND of various circuits together, and the periodically changing  AC ground wire CGND  will cause the ground wire AGND of the analog circuit to change, affecting the analog signal's voltage accuracy.

Problem 3: EMC  Experiment

The external electromagnetic radiation EMC is weaker when the signal is faint; the external electromagnetic radiation EMC is stronger when the signal is strong.

When the ground lines GND of various circuits are coupled together, the strong signal circuit's ground line GND directly interferes with the weak signal circuit's ground line  GND,  As a result, a signal source with mild external electromagnetic radiation has become a signal source with significant external electromagnetic radiation, increasing the difficulty of circuit processing EMC  studies.

Problem 4: Circuit Reliability

The circuit's ability to operate independently is greater when there are fewer parts of the signal connection; the circuit's ability to operate independently is weaker when there are more parts of the signal connection.

Consider this: if the two circuit systems A and B do not intersect, the function of circuit A cannot impact the regular operation of circuit B, and the function of circuit B cannot affect circuit A. of normal work.

The girl's emotional fluctuations will not affect the boy's mood, just as they will not affect the mood of a pair of strangers before they become lovers, because they do not have any intersection.

Connecting the ground wires of circuits with various purposes together in a circuit system is equal to increasing a link of interference between circuits, lowering