GND, short for ground terminal of wire. Represents ground wire or zero wire.

GND (ground) on the circuit diagram and circuit board represents ground wire or 0 wire. GND means common terminal, which can also be said to be ground, but this ground is not the real ground. It is a ground assumed for application. For power supply, it is the negative pole of a power supply. It is different from the earth. Sometimes it needs to be connected to the earth, sometimes it doesn’t, depending on the situation.

The signal grounding of the equipment may take a point or a piece of metal in the equipment as the grounding reference point of the signal, which provides a common reference potential for all signals in the equipment.

There are single point grounding, multi-point grounding, floating grounding and hybrid grounding.

Analysis of four grounding modes in PCB design

Single point grounding means that only one physical point in the whole circuit system is defined as the grounding reference point, and other points that need to be grounded are directly connected to this point. In low frequency circuit, there is not much influence between wiring and components. Generally, the circuit with frequency less than 1MHz adopts one point grounding.

Multipoint grounding refers to that each grounding point in electronic equipment is directly connected to the nearest grounding plane (that is, the metal base plate of the equipment). In high frequency circuit, parasitic capacitance and inductance have great influence. Usually, the circuit with frequency higher than 10MHz usually adopts multipoint grounding.

Analysis of four grounding modes in PCB design

Floating ground, that is, the ground of the circuit has no conductor connection with the earth. Virtual ground: a point that is not grounded but is equipotential with the ground.

The advantage of this circuit is that it is not affected by the electrical properties of the earth. Floating ground can make the isolation resistance between power ground (strong current ground) and signal ground (weak current ground) very large, so it can prevent the electromagnetic interference caused by the circuit coupling of common ground impedance.

The disadvantage is that the circuit is easily affected by the parasitic capacitance, which makes the ground potential of the circuit change and increases the inductive interference to the analog circuit.

“Earth” is a very important concept in electronic technology. As there are many kinds of classifications and functions of “Di”, it is easy to confuse them. Therefore, this paper summarizes the concept of “Di”.

“Grounding” includes signal grounding inside the equipment and equipment grounding. The two have different concepts and different purposes. The classical definition of “ground” is “the equipotential point or plane as the reference of circuit or system”.

1: Signal “ground”, also known as reference “ground”, is the reference point of zero potential and the common end of the circuit signal circuit.

(1) DC ground: DC circuit “ground”, zero potential reference point.

(2) AC ground: the zero line of AC. It should be distinguished from ground wire.

(3) High power amplifier: zero point potential reference network device.

(4) Analog ground: zero potential reference point of amplifier, sample and hold, a / D converter and comparator.

(5) Digital ground: also called logical ground, is the zero potential reference point of digital circuit.

(6) “Hot ground”: switching power supply does not need to use power frequency transformer, and its switching circuit “ground” is related to the municipal power grid, that is, the so-called “hot ground”, which is charged.

(7) It is also called “ground feedback circuit” because of the “ground feedback circuit”.

Signal grounding

The signal grounding of the equipment may take a point or a piece of metal in the equipment as the grounding reference point of the signal, which provides a common reference potential for all signals in the equipment.

There are single point grounding, multi-point grounding, floating grounding and hybrid grounding. Single point grounding refers to that only one physical point in the whole circuit system is defined as the grounding reference point, and other points that need to be grounded are directly connected to this point. In low frequency circuit, there is not much influence between wiring and components. Generally, the circuit with frequency less than 1MHz adopts one point grounding. Multipoint grounding refers to that each grounding point in electronic equipment is directly connected to the nearest grounding plane (that is, the metal base plate of the equipment). In high frequency circuit, parasitic capacitance and inductance have great influence. Usually, the circuit with frequency higher than 10MHz is used

Multi point grounding. Floating ground, that is, the ground of the circuit has no conductor connection with the earth. “Virtual Earth: a point that is not grounded but is equipotential with earth.” The advantage of this circuit is that it is not affected by the electrical properties of the earth. Floating ground can make the isolation resistance between power ground (strong current ground) and signal ground (weak current ground) very large, so it can prevent the electromagnetic interference caused by the circuit coupling of common ground impedance. The disadvantage is that the circuit is easily affected by the parasitic capacitance, which makes the ground potential of the circuit change and increases the inductive interference to the analog circuit. A compromise is to bridge a large discharge resistor between the floating ground and the common ground to release the accumulated charge. Pay attention to control the impedance of release resistor, too low resistance will affect the qualification of equipment leakage current.

1: Application of floating technology

A. AC power ground and DC power ground are separated

Generally, the zero line of AC power supply is grounded. However, due to the existence of grounding resistance and the current flowing on it, the zero line potential of the power supply is not the zero potential of the earth. In addition, there are many interferences on the zero line of AC power supply. If the ground of AC power supply is not separated from that of DC power supply, it will affect the normal operation of DC power supply and subsequent DC circuit. Therefore, the floating ground technology of separating AC power ground from DC power ground can isolate the interference from AC power ground.

Floating ground technology of B amplifier

For the amplifier, especially for the small input signal and high gain amplifier, any small interference signal at the input end may cause abnormal operation. Therefore, the floating ground technology of the amplifier can block the interference signal and improve the EMC capability of the amplifier.

C. precautions for floating technology

1) In order to reduce the common mode interference current in floating system, the insulation resistance of floating system to ground should be increased as much as possible.

2) Attention should be paid to the parasitic capacitance of the floating ground system. The high frequency interference signal may still be coupled to the floating ground system through the parasitic capacitance.

3) Floating technology must be combined with shielding, isolation and other electromagnetic compatibility technology to achieve better expected results.

4) When using floating ground technology, we should pay attention to the harm of static electricity and voltage counterattack to equipment and people.

2: Hybrid grounding

Hybrid grounding makes the grounding system present different characteristics at low frequency and high frequency, which is necessary in broadband sensitive circuit. The capacitor has high impedance to low frequency and DC, so it can avoid the formation of ground loop between the two modules. When the DC ground and the RF ground are separated, the DC ground of each subsystem is connected to the RF ground through a 10-100nf capacitor. The two ground should have a low impedance connection at one point, and the connection point should be selected at the point where the highest turnover speed (di / DT) signal exists.

2: Equipment grounding

In engineering practice, in addition to seriously considering the signal grounding inside the equipment, the signal grounding of the equipment, the casing and the earth are usually connected together, and the earth is taken as the grounding reference point of the equipment. The purpose of equipment grounding is

1) Protective grounding refers to making good electrical connection between the uncharged metal shell (or frame) and the grounding device during normal operation of the equipment. A kind of wiring mode set up to protect the safety of personnel. One end of the protective “ground” line is connected with the shell of the electric appliance, and the other end is reliably connected with the earth.

2) Anti static grounding, discharge the accumulated charge on the chassis, avoid the potential rise of the chassis caused by the charge accumulation, and cause the instability of the circuit.

3) Shield the ground to prevent the equipment from changing the potential of the equipment to the ground under the action of the external electromagnetic environment, resulting in the instability of the equipment.

In addition, there are lightning protection grounding and audio special ground, etc.

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