PCB Technical - Single-point and multi-point grounding in PCB design

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 too much influence between wiring and components.Usually,the circuit with frequency less than 1MHz should be grounded at one point.

GND refers to the abbreviation of the ground terminal of the wire.Represents the ground wire or the 0 wire.

The GND (Ground) on the circuit diagram and the circuit board represents the ground wire or the 0 wire.GND means the common terminal,or ground,but this ground is not a real ground. It is a ground assumed for the application,for the 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 is not needed,depending on the specific situation.

The signal ground of the device may be a point or a piece of metal in the device as the signal ground reference point, which provides a common reference potential for all signals in the device.

Single-point grounding can significantly improve the system's signal quality and anti-interference ability. Its role is mainly reflected in the following aspects:

Noise reduction: By separating different signal grounds, the effect of high frequency interference on low frequency signals can be reduced.

Improves signal transmission: In high-speed circuits, single-point grounding ensures that the signal return path is clear, thus reducing signal delay and distortion.

Facilitates Layout Optimization: The single-point grounding design provides flexibility in PCB layout, especially in complex circuits, allowing better control of the ground path and simplifying layout design.

Multi-point grounding means that each grounding point in the electronic device is directly connected to the ground plane closest to it (ie, the metal bottom plate of the device). In high-frequency circuits, the influence of parasitic capacitance and inductance is greater. Generally, circuits with frequencies greater than 10MHz often use multi-point grounding.

Do you know single-point grounding, multi-point grounding, floating ground and mixed grounding in PCB layout and design

Floating, that is, the ground of the circuit is connected to the earth without a conductor. 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 common ground impedance circuit coupling.

The disadvantage is that the circuit is susceptible to the influence of parasitic capacitance, which causes the ground potential of the circuit to change and increases inductive interference to the analog circuit.

"Earth" is a very important concept in electronic technology. Since there are many classifications and functions of "land", it is easy to confuse, so let's summarize the concept of "land".

"Grounding" includes the signal grounding inside the equipment and the equipment grounding. The concepts of the two are different and their purposes are also different. The classic definition of "ground" is "the equipotential point or plane used as a reference for a circuit or system."

One: The signal "ground" is also called the 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 wire.

(3) Power ground: zero potential reference point for high current network devices and power amplifier devices.

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

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

(6) "Hot ground": The switching power supply does not need to use a power frequency transformer, and the "ground" of its switching circuit is related to the mains power grid, the so-called "hot ground", which is live.

(7) "Cold ground": Because the high-frequency transformer of the switching power supply isolates the input and output ends; and because its feedback circuit often uses photocouplers, it can not only transmit the feedback signal, but also isolate the "ground" of both sides; so the output end is The ground is called "cold ground" and it is not charged.

Signal ground

The signal ground of the device may be a point or a piece of metal in the device as the signal ground reference point, which provides a common reference potential for all signals in the device.

There are single-point grounding, multi-point grounding, floating ground and mixed grounding. (Floating ground is mainly introduced here) 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 too much influence between wiring and components. Usually, the circuit with frequency less than 1MHz should be grounded at one point. Multi-point grounding means that each grounding point in the electronic device is directly connected to the ground plane closest to it (ie, the metal bottom plate of the device). In high-frequency circuits, the influence of parasitic capacitance and inductance is greater. Usually the frequency is greater than 10MHz circuit, often use

Multi-point grounding. Floating, that is, the ground of the circuit is connected to the earth without a conductor. 『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 common ground impedance circuit coupling. The disadvantage is that the circuit is susceptible to the influence of parasitic capacitance, which causes the ground potential of the circuit to change and increases inductive interference to the analog circuit. A compromise is to connect a large bleeder resistor between the floating ground and the common ground to release the accumulated charge. Pay attention to control the impedance of the release resistor, too low resistance will affect the qualification of the leakage current of the equipment.

Application of floating technology

Separate AC power ground from DC power ground

Generally, the neutral line of the AC power supply is grounded. However, due to the grounding 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 are often many interferences on the neutral line of the AC power supply.If the AC power supply ground is not separated from the DC power supply ground, it will affect the normal operation of the DC power supply and subsequent DC circuits.Therefore,the use of floating technology that separates the AC power ground from the DC power ground can isolate the interference from the AC power ground.

Floating technology of amplifier

For amplifiers,especially small input signals and high-gain amplifiers,any small interference signals at the input end may cause abnormal operation.Therefore,using the floating technology of the amplifier can block the entry of interference signals and improve the electromagnetic compatibility of the amplifier.

c Precautions for floating technology

1) Try to increase the insulation resistance of the floating system to the ground, so as to help reduce the common mode interference current entering the floating system.

2) PCB manufacturers must pay attention to the parasitic capacitance of the floating system to the ground. High-frequency interference signals may still be coupled to the floating system through the parasitic capacitance.

3) Floating technology must be combined with electromagnetic compatibility technologies such as shielding and isolation to achieve better expected results.

4) When using floating technology, attention should be paid to the hazards of static electricity and voltage counterattack to equipment and people.

How to choose the appropriate grounding point in the printed circuit board design.

1.Principles of grounding point selection

The choice of grounding point is mainly divided into single-point grounding and multi-point grounding. In low-frequency circuits, due to the weak inductive effect, it is usually recommended to use a single point of grounding to reduce the noise brought about by the ground loop. In high-frequency circuits, the ground impedance becomes very important, this time should be used to reduce the ground impedance multi-point grounding method .

2.Single-point grounding and multi-point grounding

The single-point grounding method is suitable for circuits with signal operating frequency less than 1MHz, in which case the loop current of grounding has a greater influence on the interference, so only one grounding point can be selected.

At signal frequencies higher than 10MHz, multiple grounding points must be selected to ensure signal integrity . Controlling the mix of grounding points for high-speed digital and linear circuits to ensure that they are connected to the power supply side separately can effectively improve the noise immunity of the circuit .

3.Ground wire design

The design of the ground wire is also very much related to the performance of the circuit. The ground wire should be as thick as possible so that it can pass three times the value of the circuit's allowable current, and the width of the ground wire should normally be greater than 3mm. If the ground wire is too thin, it may result in unstable signal levels and reduced noise immunity.

4.Importance of Loop Design

In printed circuit boards consisting only of digital circuits, in order to enhance noise immunity, designing the ground wire as a dead loop path can effectively reduce the potential difference and thus improve the consistency of the current .

5.High-density lines and microvia technology

As electronic products become multifunctional, the contact distance is gradually reduced, the signal transmission speed increases, the density of wiring between the points and the length of the localization of the enhancement of the requirements of the PCB using high-density line configuration and microvia technology. These factors contribute to the multilayer printed circuit boards have become more common, thus improving the overall circuit performance .