Do you know PCB design tips to improve the electromagnetic compatibility of circuit boards?

How much do you know about the techniques to improve the electromagnetic compatibility of circuit boards? Electromagnetic compatibility refers to the ability of electronic equipment to still work harmoniously and effectively in various electromagnetic environments. The purpose of electromagnetic compatibility design is to enable electronic equipment to suppress various external interferences, enable electronic equipment to work normally in specific electromagnetic environments, and at the same time reduce the electromagnetic interference of the electronic equipment itself to other electronic equipment.

Following the following PCB design tips can effectively improve the electromagnetic compatibility of the circuit board:

1. Choose a reasonable wire width

Since the impact interference caused by the transient current on the printed lines is mainly caused by the inductance component of the printed wires, the inductance of the printed wires should be minimized. The inductance of a printed wire is directly proportional to its length and inversely proportional to its width, so short and precise wires are beneficial to suppressing interference. Clock leads, row driver or bus driver signal lines often carry large transient currents, and printed conductors should be kept as short as possible. For discrete component circuits, the printed conductor width can fully meet the requirements when it is about 1.5mm; for integrated circuits, the printed conductor width can be selected between 0.2 and 1.0mm.

2. Adopt the correct wiring strategy

Using equal wiring can reduce the wire inductance, but the mutual inductance and distributed capacitance between the wires will increase. If the layout allows, it is best to use a tic-tac-toe mesh wiring structure. The specific method is to wire horizontally on one side of the printed circuit board and vertically on the other side. , and then connect them with metallized holes at the cross holes.

3. Avoid long-distance equal wiring

In order to suppress crosstalk between printed circuit board wires, long-distance equal wiring should be avoided when designing and wiring, the distance between wires should be as wide as possible, and signal wires should not cross with ground wires and power wires as much as possible. . Setting a grounded printed line between some signal lines that are very sensitive to interference can effectively suppress crosstalk.

4. Optimize wiring design to avoid electromagnetic radiation generated when high-frequency signals pass through printed wires

In order to avoid electromagnetic radiation generated when high-frequency signals pass through printed wires, the following points should also be paid attention to when wiring printed circuit boards: Minimize the discontinuity of printed wires, for example, the width of the wire should not change suddenly, and the corners of the wire should be Circular routing is prohibited if the angle is greater than 90 degrees. Clock signal leads are most likely to cause electromagnetic radiation interference. They should be routed close to the ground loop, and the driver should be close to the connector. Bus drivers should be located close to the bus they are intended to drive. For those leads that exit the PCB, the driver should be located immediately next to the connector.

The data bus wiring should include a signal ground wire between every two signal wires. It is best to place the ground return immediately next to the least important address leads, which often carry high-frequency currents.

5. Suppress reflection interference

In order to suppress the reflection interference that appears at the terminals of printed lines, except for special needs, the length of printed lines should be shortened as much as possible and slow circuits should be used. If necessary, terminal matching can be added, that is, a matching resistor with the same resistance value can be added to the end of the transmission line to the ground and power supply ends. According to experience, for generally fast TTL circuits, terminal matching measures should be used when the printed lines are longer than 10cm. The resistance of the matching resistor should be determined based on the maximum output drive current and absorption current of the integrated circuit.

6. Use differential signal line routing strategies in the circuit board design process

Pairs of differential signals routed very close to each other will also be tightly coupled to each other. This mutual coupling will reduce EMI emissions. Usually (of course there are some exceptions) differential signals are also high-speed signals, so high-speed design rules usually apply. This is especially true for differential signal wiring, especially when designing signal lines for transmission lines. This means that we must design the wiring of the signal line very carefully to ensure that the characteristic impedance of the signal line is continuous and constant along the signal line.

During the layout and routing process of the differential wire pair, we hope that the two PCB lines in the differential wire pair are completely consistent. This means that in practical applications, every effort should be made to ensure that the PCB traces in the differential pair have exactly the same impedance and that the trace lengths are exactly the same. Differential PCB lines are usually always routed in pairs, and the distance between them remains constant at any position along the direction of the pair. Normally, differential pairs are always routed as close together as possible. The above are some tips for improving the electromagnetic compatibility of circuit boards. I hope they can help you.