At present, electronic devices used in various electronic devices and systems are still mainly assembled by printed circuit boards. Practice has proved that even if the circuit schematic design is correct and the printed circuit board design is improper, it will have a negative impact on the reliability of electronic equipment. For example, if two thin parallel lines of a printed circuit board are very close together, the delay of the signal waveform will be formed and the reflection noise will be formed at the end of the transmission line. Therefore, in the design of printed circuit board, should pay attention to the correct method.

Grounding is an important method to control interference in electronic equipment. Most interference problems can be solved by properly combining grounding and shielding. The ground wire structure in electronic equipment includes system ground, enclosure ground (shield ground), digital ground (logic ground) and analog ground. The following points should be noted in the ground wire design:

1, the correct choice of single-point grounding and multi-point grounding

In the low-frequency circuit, the working frequency of the signal is less than 1MHz, the influence of the inductance between the wiring and the device is small, and the influence of the circulation formed by the grounding circuit on the interference is large, so the one-point grounding should be adopted. When the signal operating frequency is greater than 10MHz, the ground impedance becomes very large, at this time should try to reduce the ground impedance, should use the nearest multipoint grounding. When the working frequency is 1 ~ 10MHz, if one-point grounding is used, the length of the ground wire shall not exceed 1/20 of the wavelength, otherwise the multi-point grounding method shall be used.

2. Separate digital circuit from analog circuit

There are both high-speed logic circuit and linear circuit on the circuit board, they should be separated as far as possible, and the ground wire of the two should not be mixed, respectively connected to the ground wire of the power supply. Increase the ground area of the linear circuit as much as possible.

3. Thicken the grounding wire as much as possible

If the grounding wire is very thin, the grounding potential will change with the change of the current, causing the timing signal level of electronic equipment to be unstable and the anti-noise performance to become worse. Therefore, the grounding wire should be made as thick as possible so that it can pass through the three allowable currents located on the printed circuit board. If possible, the width of the grounding wire shall be greater than 3mm.

4, the grounding wire to form a closed loop

When designing the PCB ground wire system which only consists of digital circuit, making the ground wire into a closed loop can obviously improve the anti-noise ability. The reason for this is that there are many integrated circuit components on printed circuit board, especially in case of more components, power consumption due to restrictions of the grounding line thickness, can produce large potential difference on the knot, cause anti-noise ability to drop, if the grounding structure into the loop, would be to reduce the potential difference value, improve the ability to resist noise electronic equipment.