PCB high speed signal circuit wiring technology

PCB board design is a required course for electronic engineers, and want to design a perfect PCB board is not as easy as it seems. A perfect PCB board not only needs to be selected and set reasonably, but also has good signal transmission performance.


Rational use of multilayer board for PCB routing


In the actual design process of the PCB board, most of the engineers will choose to use the multilayer board to complete the signal wiring work, an indispensable part of the multilayer board is not only the effective means is to help engineers to reduce circuit interference. In the use of multilayer board to complete the high-speed signal circuit PCB design, engineers need to choose the reasonable layers to reduce the PCB size, make full use of the intermediate layer to set the screen, to achieve the nearest ground, can effectively reduce the parasitic inductance, shorten the length of signal transmission, reduce the cross interference between signals and so on, all these methods are very beneficial to the reliability of high-speed circuit.


The shorter the lead between the pins of a high-speed circuit device


In the process of design and layout of PCB high speed signal circuit, as far as possible to shorten the lead engineers need high-speed circuit device pins between the thought lead longer, the distributed capacitance and inductance value caused by the larger, this will lead to reflection, high speed circuit system vibration etc..


In addition to the possible shortening of the high-speed circuit element between the pin lead, in the process of PCB wiring, various high-speed circuit devices lead interlayer alternating less, is used in the process of component connection vias as little as possible. Generally speaking, a hole can bring about 0.5pF of the distributed capacitance, which will lead to a significant increase in circuit delay. At the same time, high-speed circuit wiring should pay attention to the signal line close parallel line introduced by "interference", if you can not avoid parallel distribution, reverse arrangement of large area can be in parallel to the signal line "to reduce interference. In the adjacent two layers, the direction of the line must be taken as perpendicular to each other.


For a particularly important signal line or local unit


In the design process of PCB wiring board, engineers can wire surrounded by method of some important signal lines in high speed analog signal as the clock signal, which is not easy to be disturbed by the signal line and ground protection in the periphery and the signal line to protect the caught in the middle. Because in the design process, all kinds of signal line can not form a loop, the same line can not form a current loop. However, if the loop circuit is generated, it will cause a lot of interference in the system. The wiring method of using the earth wire to surround the signal line can effectively avoid forming a loop when wiring. One or more high frequency decoupling capacitors should be located near each integrated circuit block. Analog ground wire, digital earth wire to connect to the common ground wire to use high frequency choke link. Some high speed signal lines should be specially treated: the differential signal is required to be on the same level as close as possible to the parallel line.


 

(Source: Internal data)

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