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What is the function of PCB snake routing
2020-09-25
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Author:Dag      Share

In some references of ipcb, the effect of PCB serpentine routing is as follows:

Any trace on PCB will cause time delay to the signal when passing through high frequency signal. The main function of serpentine routing is to compensate the part of "same group correlation" signal line with less delay, which usually has no or less logic processing than other signals; the typical is clock line, which usually does not need any other logic processing, so it does not need any other logic processing The delay time is less than other related signals.

PCB snake routing

PCB snake routing

The equal line length of high-speed digital PCB board is to keep the delay difference of each signal within a range, and ensure the validity of the data read by the system in the same cycle (if the delay difference exceeds one clock cycle, the data in the next cycle will be wrongly read). Generally, the delay difference is not more than 1 / 4 clock cycle, and the line delay difference per unit length is also fixed. The delay follows the line width, line length and copper thickness, The structure of the board is related, but the long wire will increase the distributed capacitance and inductance, which will lead to the signal quality. Therefore, the clock IC pins are generally connected to the RC terminal. However, the serpentine wiring does not play the role of inductance. On the contrary, the inductance will cause the high-order harmonic phase shift in the rising element of the signal, resulting in the deterioration of the signal quality. Therefore, the distance between the serpentine wires should be less than twice the line width, The smaller the rise time of the signal, the more susceptible it is to distributed capacitance and inductance

Because of different applications, it has different functions. If the serpentine line appears in the computer board, it mainly acts as a filter inductor to improve the anti-interference ability of the circuit. The serpentine routing in the main computer board is mainly used in some clock signals, such as pciclk and agpclk. It has two functions:

1. Impedance matching

2. Filter inductance.

For some important signals, such as hublink in Intel hub architecture, there are 13 hublinks running 233MHz, which must be strictly equal in length to eliminate the hidden danger caused by time delay. Winding is the solution. Generally speaking, the line spacing of serpentine routing is greater than or equal to twice the line width. The snaking wire on PCI board is to meet the wire length requirement of PCI 33MHz clock. If it is a distributed parameter LC filter in common PCB board, it can also be used as the inductance coil of radio antenna, and the short and narrow snake wire can be used as fuse, etc