The serpentine wiring function of the power supply pcb board cannot be ignored

2021-01-05 11:19:10 hongling

The serpentine wiring function of the power pcb board cannot be ignored




    Any trace on the PCB will cause a time delay to the signal when it passes a high-frequency signal. The main function of the serpentine trace is to compensate for the smaller delay parts of the "same group of related" signal lines. Usually no or less than other signals through other logic processing; the most typical is the clock line, usually it does not need any other logic processing, so its delay will be less than other related signals.




    The equal line length of the high-speed digital PCB board is to keep the delay difference of each signal within a range to ensure the validity of the data read by the system in the same cycle (when the delay difference exceeds one clock cycle, the next cycle will be read incorrectly. Data), the delay difference is generally required to not exceed 1/4 clock cycle, the line delay difference per unit length is also fixed, the delay is related to the line width, line length, copper thickness, and layer structure, but the line length will increase the distributed capacitance And distributed inductance to make the signal quality, so the clock IC pins are generally connected to RC termination, but the serpentine trace does not play the role of inductance, on the contrary, the inductance will make the higher harmonics in the rising element of the signal phase shift , Causing the signal quality to deteriorate, so the serpentine line spacing is required to be at least twice the line width.The smaller the signal rise time, the more susceptible to the distributed capacitance and distributed inductance.




    Because different applications have different functions, if the serpentine trace appears in the computer board, it mainly acts as a filter inductor to improve the anti-interference ability of the circuit. The serpentine trace in the computer motherboard is mainly used in Some clock signals, such as CIClk, AGPClk, have two functions: 1. Impedance matching 2. Filtering inductance. For some important signals, such as the HUBLink in the INTEL HUB architecture, there are 13 channels running at 233MHz. The length must be strictly equal to eliminate the hidden dangers caused by time lag. Winding is the only solution. Generally speaking, the line spacing of serpentine traces>=2 times the line width. The snake line on the PCI board is to meet the line length requirements of PCI33MHzClock. If it is a distributed parameter LC filter in a general ordinary PCB board, it can also be used as an inductance coil of a radio antenna, and the short and narrow serpentine trace can be used as a fuse, etc.