Wiring Techniques for High-Speed PCB Circuit Board Signal Integrity Design
In the design and manufacturing process of high-speed PCB circuit boards, engineers need to start from the aspects of wiring and component settings to ensure that this PCB board has good signal transmission integrity. In today's article, we will introduce some wiring techniques commonly used in PCB signal integrity design for newcomers, and hope to bring some help to the newcomers' daily learning and work.
In the design process of high-speed PCB circuit boards, the cost of the printed circuit of the substrate is directly proportional to the number of layers and the surface area of the substrate. Therefore, under the premise of not affecting the system function and stability, the engineer should use the minimum number of layers to meet the actual design needs, so that the wiring density will inevitably increase. The smaller the interval is, the larger the crosstalk between signals is, and the smaller the transmission power is. Therefore, the choice of trace size must take into account various factors.
In the PCB layout design process, the principles that engineers need to follow are the following:
First of all, in the process of wiring, the designer should minimize the bending of the leads between the pins of the high-speed circuit device, and use a 45∀ broken line to reduce the external reflection of high-frequency signals and the coupling between them.
Secondly, when conducting the wiring operation of the PCB, the designer minimizes the lead between the pins of the high-frequency circuit device and the inter-layer alternation of the lead between the pins as much as possible. High-frequency digital signal traces should be kept as far away from analog circuits and control circuits as possible.
In addition to the above-mentioned considerations for PCB layout, engineers also need to handle the issue of differential signals carefully. Because the amplitude and direction of the differential signals are equal, the magnetic fields generated by the two signal lines cancel each other out, which can effectively reduce EMI. The spacing of the differential lines often results in changes in the differential impedance. The inconsistency of the differential impedance will seriously affect the signal integrity. Therefore, in actual differential wiring, the length difference between the two signal lines of the differential signal must be controlled at the rising time Within 20% of electrical length. If conditions permit, differential traces must meet the back-to-back principle and be in the same routing layer. In the line spacing setting of differential wiring, engineers need to ensure that it is at least 1 times the line width or more. The distance between the differential trace and other signal lines should be greater than three times the line width.