PCB Board GND Design Principles and Precautions

1. PCB GND design principles

1.1. Single point grounding principle

In the PCB design process, the principle of single point grounding should be followed as far as possible. Single-point grounding means connecting all ground wires to a common location, avoiding the formation of ground wires in multiple locations to reduce interference and asymmetry in the return path. This design helps to reduce the potential difference between ground lines, thus reducing noise and interference.

However, it is important to note that the single point grounding principle does not apply in all cases. Especially in high-frequency circuits, due to the influence of ground impedance, a single point grounding may cause uneven distribution of ground current, resulting in interference. Therefore, in the high-frequency circuit, the appropriate grounding method should be selected according to the specific situation, such as multi-point grounding or hybrid grounding.

1.2. GND plane layout

In PCB design, an independent plane should be planned as far as possible to arrange GND. This plane can be used as a path for current return and play a role in shielding electromagnetic interference. At the same time, to avoid interference, the GND plane should be as far away from the signal line and power line as possible.

The GND plane should be arranged as evenly as possible to avoid excessive local current density. In addition, the GND plane should also be kept at a certain distance from the power plane to reduce the influence of power noise on the GND plane.

1.3. Layer cabling

For large and complex boards, it is recommended that the GND be designed in layers. GND can be divided into multiple levels and routed according to different parts of the circuit, thus reducing the asymmetry of the return path and better shielding interference. Layering helps to reduce the ground impedance and improve the anti-interference ability of the circuit.

1.4. GND separation from signal lines

In PCB design, GND and signal lines should be separated as far as possible to avoid mutual interference caused by their common layer on the same plane. You can divide GND planes and route cables separately from signal cables by layers. This design is helpful to reduce the coupling interference between the signal line and the ground wire, and improve the transmission quality of the signal.

2. PCB circuit board GND design precautions

2.1. Avoid excessively long GND return paths

In circuit board design, the length of GND return path should be shortened as much as possible. Too long return path will increase the impedance of the return current and affect the stability of the circuit. Therefore, in the design process, the layout of the ground wire should be reasonably planned, and the return path should be shortened as much as possible.

2.2. Prevent GND backflow interference

The current in the GND return path may cause electromagnetic interference and affect the normal operation of the circuit. In order to eliminate this interference, filter inductors and capacitors can be added to the return path for isolation and filtering. In addition, the GND backflow interference can be reduced by optimizing the ground wire layout and reducing the ground wire impedance.

2.3. GND crosses signal cables

When PCB cables are routed, try to avoid the cross crossing between GND and signal lines. Since the signal line carries the signal, GND plays a shielding role, and the crossing of the two will cause the signals to interfere with each other. Therefore, the paths of GND and signal lines should be reasonably planned in the wiring process to minimize the possibility of crossing. If crossing cannot be avoided, measures such as vertical crossing and increasing shielding layers can be taken to reduce interference.

2.4. Width of the ground cable

The width of the grounding wire should be as thick as possible to improve its current carrying capacity and anti-interference ability. If the grounding wire is very thin, the grounding potential changes with the change of current, resulting in the timing signal level of the electronic device is unstable, and the anti-noise performance becomes bad. Therefore, the ground wire should be as thick as possible, so that it can pass three times the allowable current of the printed circuit board. In the actual design, the width of the ground wire should be greater than 3mm to ensure its stability and reliability.

2.5. Select the correct single-point grounding and multi-point grounding

In low-frequency circuits (signal operating frequency is less than 1MHz), because the inductance between the wiring and the device is less influential, and the circulation formed by the grounding circuit has a greater impact on interference, so a point grounding should be used. This design helps reduce potential differences and circulation interference between ground lines.

However, in high-frequency circuits (signal operating frequency is greater than 10MHz), the ground impedance becomes very large, and the ground impedance should be reduced as much as possible, and the nearest multipoint grounding should be used. Multipoint grounding helps to reduce ground impedance and reduce high-frequency noise and interference.

When the operating frequency is 1~10MHz, if one point grounding is used, the ground length should not exceed 1/20 of the wavelength, otherwise the multi-point grounding method should be used. In addition, when there are both high-speed logic circuits and linear circuits on the circuit board, they should be separated as far as possible, and the ground wires of the two should not be mixed, and the ground wires of the power supply are connected respectively. This reduces interference and noise between different circuits.

2.6. Increase the grounding area of the linear circuit

In PCB design, the grounding area of the linear circuit should be increased as much as possible. This helps to reduce the ground impedance and noise voltage, and improve the anti-interference ability of the circuit. At the same time, increasing the grounding area can also increase the heat dissipation area, which helps to reduce the operating temperature of the circuit.

2.7. The grounding structure is a loop

In PCB design, if there are many integrated circuit components on the circuit board, especially when there are many power-consumption components, due to the limitation of the thickness of the ground wire, a large potential difference will be generated on the ground junction, causing the anti-noise ability to decrease. At this time, the ground can be structured into a loop to reduce the potential difference and improve the anti-noise ability of the electronic device. This design helps reduce potential differences and noise interference between ground lines.

2.8. Combine shielding and grounding

In PCB design, shielding and grounding are important methods to control interference. By using the proper combination of shielding and grounding, most interference problems can be solved. For example, in a high-frequency circuit, a metal shielding box can be used to shield the high-frequency components, and the shielding box can be grounded to eliminate high-frequency noise and interference. In addition, shielding measures such as shielding layers and shielding strips can also be used to reduce electromagnetic interference and noise.

2.9. Pay attention to the choice of ground point

In PCB design, the choice of ground point is also very important. The ground point should be as close as possible to the component or part of the circuit that needs to be grounded to reduce the ground length and impedance. At the same time, the ground point should also be as far away from the noise source and interference source as possible to reduce the impact of noise and interference on the circuit.

2.10. Follow the design specification

In the PCB GND design, the relevant design specifications and standards should also be followed. For example, the continuity, integrity and reliability of the grounding wire should be ensured; Avoid breakpoints, cracks or poor contact on the grounding line; Ensure that the grounding cable is correctly and reliably connected to the power supply end and the signal end. These specifications and standards help ensure the correctness and reliability of PCB GND designs.

3. Summary of GND design of PCB circuit board

PCB GND design is a key link to ensure stable circuit performance and reduce interference and noise. In the design, the principles of single point grounding, reasonable planning of GND plane layout, layered wiring, separate routing of GND and signal lines should be followed. Pay attention to avoid too long GND return path, prevent GND return interference, reduce the cross crossing between GND and signal lines, etc. At the same time, the method of single point grounding and multi-point grounding should be correctly selected, the grounding area of the linear circuit should be increased, and the grounding structure should be formed into a loop to improve the anti-interference ability of the circuit. By following these principles and considerations and following the relevant design specifications and standards, you can ensure the correctness and reliability of the PCB GND design and improve the performance and stability of the circuit.