What are the differences among the many “grounds” in electronic technology?

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What are the differences among the many “grounds” in electronic technology? [Copy link]

XGND is the abbreviation of the wire end. It stands for the ground or zero line. GND (Ground) on the circuit diagram and the circuit board stands for the ground or zero line. GND means the common end, or the ground, but this ground is not the real 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 does not, depending on the specific situation. The signal of the device may be a point or a piece of metal in the device as the reference point of the signal, which provides a common reference potential for all signals in the device. There are single-point grounding, multi-point grounding, floating grounding 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, there will not be much impact between wiring and components. Usually, circuits with frequencies less than 1MHz use single-point grounding. Multi-point grounding means that each grounding point in an electronic device is directly connected to the nearest ground plane (i.e., the metal bottom plate 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 the ground of the circuit is not connected to the earth by a conductor. Virtual ground: a point that is not grounded but is equipotential with the earth. Its advantage is that the circuit is not affected by the electrical properties of the earth. Floating ground can make the isolation resistance between the power ground (strong electric ground) and the signal ground (weak electric ground) very large, so it can prevent the electromagnetic interference generated by the coupling of the common ground impedance circuit. Its disadvantage is that the circuit is easily affected by parasitic capacitance, which causes the ground potential of the circuit to change and increases the inductive interference to the analog circuit. "Ground" is a very important concept in electronic technology. Since there are many types and functions of "ground", it is easy to confuse, so the concept of "ground" is summarized below. "Grounding" includes signal grounding inside the device and equipment grounding. The two concepts are different and the purposes are also different. The classic definition of "ground" is "an equipotential point or plane used as a reference for a circuit or system." 1: Signal "ground" is also called reference "ground", which is the reference point of zero potential and the common end of the circuit signal loop. (1) DC ground: DC circuit "ground", zero potential reference point. (2) AC ground: the neutral line of AC power. It should be distinguished from the ground line. (3) Power ground: the zero potential reference point of high current network devices and power amplifier devices. (4) Analog ground: the zero potential reference point of amplifiers, sample-and-hold devices, A/D converters and comparators. (5) Digital ground: also called logic ground, which is the zero potential reference point of digital circuits. (6) "Hot ground": The switching power supply does not need to use an industrial frequency transformer. The "ground" of its switching circuit is related to the mains power grid, which is the so-called "hot ground". It is energized. (7) "Cold ground": Since the high-frequency transformer of the switching power supply isolates the input and output ends; and since its feedback circuit often uses an optocoupler, which can both transmit feedback signals and isolate the "grounds" of both sides; the ground of the output end is called "cold ground", which is not energized. Signal grounding The signal grounding of the device may be a point or a piece of metal in the device as the grounding reference point of the signal, which provides a common reference potential for all signals in the device. There are single-point grounding, multi-point grounding, floating grounding and mixed grounding. (Here we mainly introduce floating grounding) Single-point grounding means that only one physical point in the entire circuit system is defined as the grounding reference point, and all other points that need to be grounded are directly connected to this point. In low-frequency circuits, there will not be much impact between wiring and components. Usually, circuits with frequencies less than 1MHz use single-point grounding. Multi-point grounding means that each grounding point in the electronic device is directly connected to the ground plane closest to it (that is, the metal bottom plate 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 the ground of the circuit is not connected to the earth with a conductor. "Virtual ground: a point that is not grounded but has the same potential as the ground. " Its 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 power ground) and signal ground (weak power ground) very large, so it can prevent the electromagnetic interference caused by the coupling of common ground impedance circuit. Its disadvantage is that the circuit is susceptible to parasitic capacitance, which causes the ground potential of the circuit to change and increases the inductive interference to the analog circuit. A compromise is to connect a large-resistance discharge resistor between the floating ground and the common ground to release the accumulated charge. Pay attention to controlling the impedance of the discharge resistor. Too low resistance will affect the qualification of the leakage current of the equipment. 1: Application of floating ground technology a. Separation of AC power ground and DC power ground. Generally, the neutral line of the AC power supply is grounded. However, due to the existence of grounding resistance and the current flowing through it, the neutral line potential of the power supply is not the zero potential of the earth. In addition, there are often a lot of interferences on the neutral line of the AC power supply. If the AC power ground and the DC power ground are not separated, it will affect the normal operation of the DC power supply and the subsequent DC circuit. Therefore, the floating ground technology that separates the AC power ground from the DC power ground can isolate the interference from the AC power ground. b Floating ground technology of amplifier For amplifiers, especially those with small input signals and high gain, any small interference signal at the input end may cause abnormal operation. Therefore, the floating ground technology of amplifiers can block the entry of interference signals and improve the electromagnetic compatibility of amplifiers. c Precautions for floating ground technology 1) Try to increase the insulation resistance of the floating ground system to the ground, which is conducive to reducing the common mode interference current entering the floating ground system. 2) Pay attention to the parasitic capacitance of the floating ground system to the ground. High-frequency interference signals may still be coupled into the floating ground system through parasitic capacitance. 3) Floating ground technology must be combined with electromagnetic compatibility technologies such as shielding and isolation to achieve better expected results. 4) When using floating ground technology, attention should be paid to the harm of static electricity and voltage counterattack to equipment and personnel. 2: Mixed grounding Mixed grounding makes the grounding system present different characteristics at low and high frequencies, which is necessary in broadband sensitive circuits. Capacitors have higher impedance to low frequencies and DC, so they can avoid the formation of ground loops between 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 grounds should be connected at a low impedance at one point, and the connection point should be selected at the point where the highest flip speed (di/dt) signal exists. 2: Equipment grounding In engineering practice, in addition to carefully considering the signal grounding inside the equipment, the signal ground and the casing of the equipment are usually connected to the ground, and the ground is used as the grounding reference point of the equipment. The purpose of equipment grounding is 1) protection ground. Protection grounding is to make a good electrical connection between the metal casing (or frame) that is not charged during normal operation of the equipment and the grounding device. A wiring method set up to protect personnel safety. One end of the protection "ground" wire is connected to the housing of the electrical appliance, and the other end is reliably connected to the ground. 2) Anti-static grounding, discharge the charge accumulated on the chassis, avoid the accumulation of charge causing the chassis potential to increase, causing unstable circuit operation. 3) Shielding ground, to prevent the equipment from changing the potential of the equipment to the ground under the influence of the external electromagnetic environment, causing unstable equipment operation. In addition, there are lightning protection grounding and dedicated audio ground in audio equipment, etc.