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GND refers to the abbreviation of the ground terminal of the wire. Represents the ground wire or 0 wire.
GND (Ground) on the circuit diagram and on the circuit board represents the ground wire or 0 wire. GND means the common terminal, which can also be said to be the ground, but this ground is not the true ground. It is a ground assumed for the application. For the power supply, it is the negative pole of the power supply. It is different from the earth. Sometimes it needs to be connected to the earth, and sometimes it doesn't, depending on the situation.
The signal ground of the device may be a point or a piece of metal in the device as the ground reference point of the signal. It provides a common reference potential for all signals in the device.
There are single point grounding, multi-point grounding, floating ground and mixed grounding
Single-point grounding means that only one physical point in the entire circuit system is defined as the ground reference point, and all other points that need to be grounded are directly connected to this point. In low-frequency circuits, wiring and components do not have much influence on each other. Generally, circuits with frequencies less than 1MHz are grounded at one point.
Multi-point grounding means that each ground point in an electronic device is directly connected to the ground plane closest to it (that is, the metal base of the device). In high-frequency circuits, parasitic capacitance and inductance have a greater impact. Usually circuits with frequencies greater than 10MHz often use multi-point grounding.
Floating ground means that there is no conductor connection between the ground of the circuit and the earth. Virtual ground: A point that is not grounded but has the same potential as the ground.
The advantage is that the circuit 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 electromagnetic interference caused by circuit coupling of common ground impedance.
The disadvantage is that the circuit is easily affected by parasitic capacitance, which causes the ground potential of the circuit to change and increases the induced interference to the analog circuit.
"Ground" is a very important concept in electronic technology. Since there are many classifications and functions of "earth" and it is easy to be confused, let's summarize the concept of "earth".
"Grounding" includes the signal grounding inside the equipment and the equipment grounding. The two have different concepts and different purposes. The classic definition of "ground" is "an equipotential point or plane that serves as the reference for a circuit or system."
The signal "ground" is also called the reference "ground", which is the reference point of zero potential and is also the common terminal that forms the signal loop of the circuit.
- DC ground: DC circuit "ground", zero potential reference point.
- AC ground: The neutral line of alternating current. It should be distinguished from the ground wire.
- Power ground: the zero-potential reference point of high-current network devices and power amplifier devices.
- Analog ground: The zero-potential reference point for amplifiers, track-and-holds, A/D converters, and comparators.
- Digital ground: Also called logic ground, it is the zero-potential reference point of digital circuits.
- "Hot ground": The switching power supply does not need to use a power frequency transformer. The "ground" of its switching circuit is related to the mains power grid, which is the so-called "hot ground", which is live.
- "Cold ground": Because the high-frequency transformer of the switching power supply isolates the input and output ends; and because its feedback circuit commonly uses photoelectric couplers, it can not only transmit feedback signals but also isolate the "ground" of both sides; so the ground of the output end is called Being a "cold ground", it is not electrically charged.
1, signal grounding
The signal ground of the device may be a point or a piece of metal in the device as the ground reference point of the signal. It provides a common reference potential for all signals in the device.
There are single-point grounding, multi-point grounding, floating ground and hybrid grounding. (Here we mainly introduce floating ground) Single-point grounding means that only one physical point in the entire circuit system is defined as the ground reference point, and all other points that need to be grounded are directly connected to this point. In low-frequency circuits, wiring and components do not have much influence on each other. Generally, circuits with frequencies less than 1MHz are grounded at one point. Multi-point grounding means that each ground point in an electronic device is directly connected to the ground plane closest to it (that is, the metal base of the device).
In high-frequency circuits, parasitic capacitance and inductance have a greater impact. Usually circuits with frequencies greater than 10MHz often use multi-point grounding. Floating ground means that there is no conductor connection between the ground of the circuit and the earth. "Virtual ground: A point that is not grounded but has the same potential as the ground. 』The advantage is that the circuit 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 electromagnetic interference caused by circuit coupling of common ground impedance. The disadvantage is that the circuit is easily affected by parasitic capacitance, which causes the ground potential of the circuit to change and increases the induced interference to the analog circuit. A compromise is to place a large value bleeder resistor across the floating ground and common ground to discharge the accumulated charge.
Pay attention to controlling the impedance of the release resistor. Too low resistance will affect the qualification of the device leakage current.
2. Application of floating technology
2.1. Separate the AC power ground and DC power ground.
Generally, the neutral wire of the AC power supply is grounded. However, due to the existence of ground resistance and the current flowing through it, the zero line potential of the power supply is not the zero potential of the earth. In addition, there is often a lot of interference on the neutral line of the AC power supply. If the ground of the AC power supply is not separated from the ground of the DC power supply, it will affect the normal operation of the DC power supply and subsequent DC circuits. Therefore, using floating technology that separates the AC power ground from the DC power ground can isolate interference from the AC power ground wire.
b. Floating technology of amplifier
For amplifiers, especially amplifiers with small input signals and high gains, any small interference signal at the input end may cause abnormal operation. Therefore, using the floating ground technology of the amplifier can block the entry of interference signals and improve the electromagnetic compatibility of the amplifier.
c. Precautions for floating technology
- Try to increase the ground insulation resistance of the floating system as much as possible, which will help reduce the common mode interference current entering the floating system.
- Pay attention to the parasitic capacitance of the floating system to the ground. High-frequency interference signals may still be coupled into the floating system through the parasitic capacitance.
- Floating technology must be combined with electromagnetic compatibility technologies such as shielding and isolation to achieve better expected results.
- When using floating technology, attention should be paid to the hazards to equipment and people caused by static electricity and voltage backlash.
3. Hybrid grounding
Hybrid grounding gives the grounding system different characteristics at low and high frequencies, which is necessary in broadband sensitive circuits. The capacitor has a high impedance to low frequencies and DC, so it can avoid the formation of ground loops between the two modules. When separating the DC ground and the RF ground, connect the DC ground of each subsystem to the RF ground through a 10-100nF capacitor. The two grounds should be connected with low impedance at one point, and the connection point should be selected at the highest flip speed ( di/dt) point where the signal exists.
3.1. Connect the equipment to the ground
In engineering practice, in addition to carefully considering the signal grounding inside the equipment, the signal ground of the equipment, the chassis and the earth are usually connected together, and the earth is used as the grounding reference point of the equipment. The purpose of connecting equipment to the earth is:
- Protective grounding is to make a good electrical connection between the metal shell (or frame) and the grounding device that is not charged during normal operation of the equipment. A wiring method set up to protect personnel safety. One end of the protective "ground" wire is connected to the electrical appliance shell, and the other end is reliably connected to the earth.
- Anti-static grounding discharges the charge accumulated on the chassis to prevent the accumulation of charge from raising the potential of the chassis and causing unstable circuit operation.
- Shield the ground to prevent the equipment from changing its potential to the earth under the action of the external electromagnetic environment, causing instability in the operation of the equipment.
In addition, there are lightning protection grounding and dedicated audio ground in the stereo, etc.