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We all know that when designing a PCB circuit board, if it is just an ordinary board, it is enough to do an accurate design of the mechanical size. However, if you encounter high-frequency signals, load lines or long lines, etc., special treatment must be performed on these lines. Otherwise, it is likely to cause a series of signal interference such as reflections and crosstalk between lines. problem. Therefore, when we are doing circuit design, especially when doing high-speed PCB design, we must do a good job in line signal imitating interference, and shielding measures are very necessary. The following is the PCB circuit board wiring, how to do the EMC design specifically?
PCB circuit board
1. Appropriate wire width
When selecting the width of the wire, it is necessary to ensure both electrical performance and easy production, which is usually determined by the smaller current value it bears. In order to reduce the electromagnetic interference impact caused by the transient current on the printed board, it is necessary to control the line width in the design. Transient interference is generally caused by the inductance of the wire, and its inductance is proportional to the length of the wire and inversely proportional to the line width. For signal lines that often have large transient currents, short and wide wires should be used. If the layout space permits, use a grid-shaped layout structure as much as possible.
2. The main points of component wiring
Component wiring design, mainly consider several aspects: First, electrical performance; when we are wiring, we try to put the components closely connected with the wiring together, and the layout of high-speed lines should be as short as possible, power devices and small signal devices To separate the layout. The second is the location; whether the design is beautiful and tidy, whether it is convenient for function testing, later interface and connection use. In high-speed systems, the transmission delay of grounding and interconnecting lines is also the first design factor that we need to consider. The transmission time of signal transmission lines has a great impact on the total system speed of the circuit. If it is used where high-speed lines are used Ordinary interconnection lines will increase the delay time and greatly reduce the system speed.
3. Wiring rules for high-frequency and high-speed signals
Normally, equal wiring can reduce the inductance between wires, but in order to suppress the crosstalk of PCB circuit wires, we should try to avoid long-distance equal wiring when designing the wiring; when designing printed wires, we should avoid sharp turns and try to design as It has a uniform curve with a certain radian; there are components with large currents in the circuit, and the ground wire should be separated as much as possible to avoid noise interference. Grounding is set between small signal or sensitive signal wires; high-speed signals adopt differential signal wiring design, The two differential lines in the positive and negative pairs are always coupled to each other on the transmission line, which effectively reduces the electrical noise effect of the signal.
