The anti-interference   design of the printed circuit board in the PCB design   has a close relationship with the specific circuit. Here, only some common   measures of the PCB anti-interference design are explained.

1.Power cord design

According to the current of the printed circuit board, try to increase the width of the power line and reduce the loop resistance. At the same time, the

direction of the power line and the ground line are consistent with the

direction of data transmission, which helps to enhance the anti-noise   capability.

2. Principles of ground wire design

(1) The digital ground is separated from the simulated ground. If there are   both logic and linear circuits on the board, they should be separated as much as possible. The ground of the low-frequency circuit should be grounded   in parallel with a single point. If the actual wiring is difficult, it can be partially   connected and then grounded in parallel. The high-frequency circuit   should   adopt multi-point series grounding, the ground wire should be short   and   rented, and the grid-like large-area foil should be used as much as possible   around the high-frequency electronic components.

(2) The grounding wire should be as thick as possible. If the grounding wire   uses a very thin line, the ground potential changes with the change of the   current, which reduces the noise immunity. Therefore, the ground wire should be thickened so that it can pass three times the allowable current on the   printed board. If possible, the grounding wire should be 2~3mm or more.

(3) The grounding wire constitutes a closed loop. In a printed circuit board   composed only of digital circuits, the grounding circuit is mostly formed into   a ring circuit to improve the anti-noise capability.

3. Untwisting capacitor configuration

One of the usual practices in PCB design is to configure appropriate   decoupling capacitors at various critical points in the printed board. The   general configuration principle for the untwisting capacitor is:

(1) The power input terminal is connected to an electrolytic capacitor of 10~100uf. If possible, it is better to pick up 100uF or more.

(2) In principle, each integrated circuit chip should be equipped with a 0.01pF   ceramic capacitor. If there is not enough gap in the printed board, a 1~10pF   tantalum capacitor can be arranged every 4~8 chips.

(3) For devices with weak anti-noise capability and large power supply changes during shutdown, such as   RAM and ROM storage devices, the decoupling capacitor should be directly   connected between the power cable and the ground of the chip.

(4) The capacitor leads should not be too long, especially the high-frequency bypass capacitors must not have leads.

(5) When there are contactors, relays, buttons and other components in the   PCB board. A large spark discharge is generated when operating them, and   an RC circuit must be used to absorb the discharge current. Generally, R takes 1~2K, and C takes 2.2~47UF.

(6) The input impedance of CMOS is very high and it is susceptible to induction. Therefore, it is necessary to ground or connect the power supply to the   unused terminal during use.