About grounding: Digital ground, analogue ground, signal ground, AC ground, DC ground, shielding ground, floating ground

　

About grounding: Digital ground, analogue ground, signal ground, AC ground, DC ground, shielding ground, floating ground

In addition to the correct grounding design, installation, but also to properly carry out a variety of different signal grounding treatment. In the control system, there are roughly the following types of ground:

(1) Digitally: Also called logically, is the 0 potential of various switching volume (digital) signals.

(2) Analog ground: is a variety of analog signal 0 potential.

(3) Signal ground: Usually the ground of the sensor.

(4) AC ground: The ground of AC power supply, this kind of ground is usually the ground that produces noise.

(5) DC: DC power supply to the ground.

(6) Shielding ground: Also called the chassis ground, to prevent electrostatic induction and magnetic induction and set.

The above-ground processing is an important problem in system design, installation and commissioning.

Here are some suggestions on grounding:

(1) The control system should use a little grounding. In general, the high-frequency circuit should be near the multipoint grounding, low-frequency circuit should be a little ground. In low-frequency circuits, the inductance between the wiring and components is not a major problem, but the ground-formed loop interference has a large impact, it is often used as a point of contact location; But a bit of grounding is not suitable for high frequency, because at high frequencies, there is inductance on the ground to increase the ground impedance, while the line between the inductance coupling. In general, the frequency is below 1MHz, can be grounded at a point, more than 10MHz, the use of multi-point grounding, between the 1~10mhz can be a point of grounding, can also be multi-point grounding.

(2) The communication ground and the signal ground cannot be shared. Since there will be several MV or even several v voltages between two points of a power ground, this is a very important interference for low-level signal circuits and must therefore be isolated and prevented.

(3) Comparison of floating ground and grounding. The whole machine floating empty namely the system each part and the Earth floats, this method is simple, but the whole system and the Earth insulation resistance cannot be less than 50mω. This method has a certain anti-jamming ability, but once the insulation decreases, it will cause interference. Another way is to ground the chassis, the rest of the floating space. This method has strong anti-jamming ability, safe and reliable, but it is more complicated to realize.

(4) Simulated ground. The connection of the simulated ground is very important. In order to improve the ability of anti-common mode interference, shielded float technology can be used for analog signal. For the specific analog signal grounding treatment should be strictly in accordance with the requirements of the Operation manual design.

(5) Shielding ground. In order to reduce the capacitance coupling noise, accurate detection and control in the control system, it is necessary to use shielding measures for the signal. Depending on the shielding purpose, the connection method of the shielding ground is different. Electric field shielding solves the problem of distributed capacitance, generally connected to the Earth, electromagnetic shielding mainly avoid radar, radio and other high-frequency electromagnetic field radiation interference. The use of low-resistance metal material is made of high conductivity, can be connected to the Earth. Magnetic shielding to prevent magnets, motors, transformers, coils and other magnetic induction, the shielding method is to use high-conductivity magnetic materials to make the magnetic circuit closed, generally connected to the Earth as well. When the signal circuit is a bit grounded, the shielding layer of the low-frequency cable should also be a bit grounded. If the shielding layer of the cable has more than one location, a noise current will be generated to form a source of noise interference. When a circuit has an ungrounded signal source connected to an amplifier grounded in the system, the shield of the input bell to the public side of the amplifier, whereas the input terminal of the amplifier should be connected to the common side of the signal source when the grounded signal source is attached to an ungrounded amplifier in the system.

For the grounding of the electrical system, according to the requirements of grounding and the purpose of classification, can not be similar to the ground simply, arbitrarily connected together, but to be divided into a number of independent grounding subsystem, each subsystem has its common grounding point or grounding trunk, finally connected together, the implementation of the total grounding.

Q1: why grounding?

Answer: The introduction of grounding technology was originally designed to prevent electrical or electronic equipment such as lightning strikes and the protective measures taken, the purpose is to the lightning generated by lightning current through the lightning rod into the Earth, thereby playing a role in protecting the building. At the same time, grounding is also an effective means of protecting personal safety, when a certain cause of the phase line (such as bad wire insulation, line aging, etc.) and equipment shell touch, the equipment shell will have a dangerous voltage generation, the resulting fault current will flow through the PE line to the Earth, thereby playing a protective role. With the development of electronic communications and other digital fields, it is far from sufficient to consider only lightning protection and safety in grounding systems. In communication systems, for example, the interconnection of signals between a large number of devices requires that each device have a benchmark ' ground ' as a reference to the signal. And with the complexity of electronic equipment, signal frequency is more and more high, therefore, in the grounding design, the interference between the signal and other electromagnetic compatibility issues must be given special attention, otherwise, improper grounding will seriously affect the reliability and stability of the system operation. Recently, the concept of "ground" has also been introduced into the signal reflow technology of high-speed signals.

Q2: Definition of grounding

Answer: In the modern grounding concept, for line engineers, the term is usually referred to as the ' line voltage reference point '; for system designers, it is often a cabinet or rack; For an electrical engineer, it's green.

Safety ground or the meaning of receiving the Earth. A more general definition is that "grounding is the low impedance channel in which the current returns to its source." Note that the requirements are "low impedance" and "pathway".

Q3: Common grounding symbols

answer:pe,pgnd,fg-protected ground or chassis; Bgnd or dc-return-DC -48v (+24V) power supply (battery) reflux; gnd-workplace; dgnd-Digital ground;

Agnd-simulated ground; Lgnd-Lightning Protection Ground

GND is often designated as a voltage reference base in the circuit.

In electrical sense, gnd is divided into power source and signal ground. PG is the abbreviation for power Ground. The other is Signal Ground (signal ground). In fact they may be linked together (not necessarily mixed together oh!). Two names, mainly to facilitate the analysis of the circuit.

Further, there are two types of "ground" that must be differentiated due to different circuit forms: digitally, simulated.

Both the digital and the analog ground have the signal ground, the power ground two kinds of situation. Between the digital and analog ground, some circuits can be connected directly, some circuits to be connected with reactors, some circuits are not connected.

Q4: Suitable grounding method

Answer: Grounding is available in a variety of ways, with single-point grounding, multi-point grounding, and mixed-type grounding. And the single-point grounding is divided into series single-point grounding and parallel single-point grounding. In general, single-point grounding is used for simple circuits, grounding between different functional modules, and low-frequency (F<1mhz) electronic circuits. When designing high frequency (F>10mhz) circuits, it is necessary to use multi-point grounding or multilayer board (complete ground plane layer).

Q5: Introduction to signal reflow and cross-segmentation

Answer: For an electronic signal, it needs to find a way to return the lowest impedance current to the ground, so how to handle this signal reflux becomes very critical.

First, according to the formula can be known, radiation intensity is proportional to the area of the loop, that is, the longer the path to go back, the more the formation of the ring, its external radiation interference is greater, so, PCB cloth board when necessary to minimize the power loop and signal loop area.

Second, for a high-speed signal, provide a good signal reflow can guarantee its signal quality, this is because the characteristic impedance of the transmission line on the PCB is generally based on the formation (or power layer) for reference to calculate, if there is a continuous ground plane near the high-speed line, so that the impedance of this line can remain continuous, If there is no reference near the segment, the impedance will change, and the discontinuous impedance will affect the integrity of the signal.

Therefore, the wiring when the high-speed line to be assigned to a layer near the ground plane, or the high-speed line and walk one or two ground, play the shielding and provide a return to the nearest function.

Third, why the wiring when possible to avoid cross-power division, which is also because the signal across the different power layer, its return path will be very long, easy to be disturbed. Of course, not strict requirements can not cross the power division, for low-speed signal is possible, because the resulting interference compared to the signal can not be concerned. For high-speed signals to be carefully checked, try not to cross, you can adjust the power supply section of the route. (This is said for multiple power supply of multilayer boards)

Q6: Why separate the analog and the digital, and how do we separate them?

Answer: Analog and digital signals are going back to the ground, because the digital signal changes fast, so that the noise caused by the digital ground will be very large, and the analog signal needs a clean reference work.

If the analog and digital mix together, the noise will affect the analog signal.

In general, the analog and digital ground to be processed separately, and then through the thin line of wire to join together, or single point to connect together. The general idea is to try to block the noise from the digital ground to the simulated ground. Of course, this is not very strict requirements of the analog and digital must be separated, if the analog part of the number is still very clean in the vicinity can be combined.

Q7: How is the signal on the veneer grounded?

Answer: For the general device, the nearest ground is the best, using a full flat layer design, for the general signal grounding is very easy, the basic principle is to ensure continuity of the line, reduce the number of vias; close to ground plane or power plane, etc.

Q8: How to ground the interface device of a single board?

Answer: Some veneer will have external input and output interface, such as serial connector, network port RJ45 connector, and so on, if the grounding of their design is not good also will affect the normal work, such as the network port interconnection error code, packet loss, and will become an external source of electromagnetic interference, the board noise outward sent. In general, separate a separate interface, the connection with the signal ground by a fine line of connection, you can string 0 ohms or a small resistance resistor. Thin lines can be used to block the signal from the ground noise over the interface to come up. In the same way, the filtering of the interface and the interface power supply should also be considered carefully.

Q9: How is the shielding layer of the cable with the shield grounded?

Answer: Shielded cable shielding layer is to receive a single board interface on the ground and not the signal ground, this is because the signal on the ground has a variety of noise, if the shielding layer received a signal on the ground, the noise voltage will drive the common mode current along the shielding layer outward interference, so the design of bad cable is generally the largest noise output source of EMI. Of course, the premise is that the interface is also very clean mixed circuit inside to do the marking, VCC represents the analog signal power, GND represents the analog signal ground, VDD represents a digital signal power supply, VSS represents a digital power supply ground.

VCC mainly represents the power supply of the bipolar circuit, C represents the collector collector, the power supply is generally connected to the NPN collector (or PnP emitter), the integrated circuit just appeared when only the NPN tube, and then the integrated PNP tube. The Vdd/vss generally represents the power supply and "ground" of the MoS circuit, and d/s respectively represents the drain (drain)/source (source) of the MoS tube.

First, explain the meaning of the circuit vcc:c=circuit, that is, the voltage of the access circuit;

Vdd:d=device indicates the meaning of the device, that is, the operating voltage inside the device;

Vss:s=series denotes the meaning of a public connection, usually referred to as the circuit's common ground terminal voltage.

Ii. description

1, for the digital circuit, VCC is the power supply voltage of the circuit, VDD is the operating voltage of the chip (usually VCC>VDD), the VSS is the pick-up location.

2. Some ICS have both a VDD pin and a VCC pin, indicating that the device itself has a voltage conversion function.

3. In the presence effector (or COMs device), VDD is the drain, VSS is the source, and Vdd and VSS refer to the component pin, not the supply voltage.

VDD: Supply voltage (unipolar device), Supply voltage (4000 series digital circuit), drain voltage (field effect tube)

VCC: Supply voltage (bipolar device), supply voltage (74 series digital circuit), voice carrier (voice controlled Carrier)

VSS: Ground or power negative

VEE: Negative voltage supply, field effect tube source (S)

VPP: Programming/erasing voltage.

Detailed

In an electronic circuit, VCC is the supply voltage of the circuit, and VDD is the operating voltage of the chip:

Vcc:c=circuit represents the meaning of the circuit, that is, the voltage of the access circuit, d=device means the device, that is, the operating voltage inside the device, in the ordinary electronic circuit, general VCC>VDD!

Vss:s=series indicates the meaning of a public connection, that is, the negative.

Some ICs have VCC and VDD at the same time, and the device has a voltage conversion function.

In the "field effect" is the COMs element, VDD is the CMOS drain pin, VSS is the CMOS source pin, which is the component pin symbol, it does not have "VCC" name, your problem contains 3 symbols, Vcc/vdd/vss, which is clearly the circuit symbol

Several grounding symbols

The 1th one I used as a power supply positive or digital circuit VCC, without the ground.

The 2nd one I used as a digital or digital analogue to the public place.

The 3rd is used as a mock ground.

The 4th, of course, is the chassis casing or the housing is connected to the Earth.

About grounding: digital, analogue, signal, AC, DC, shielded, floating