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Why do PCB boards have serpentine routing
Add time:2020/11/6 10:22:29 From: Hits:2612

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

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 fixed, and the delay follows the line width, line length and copper thickness However, if the wire length is too long, the distributed capacitance and inductance will be increased and the signal quality will be improved. Therefore, the clock IC pins are generally connected with RC terminals. However, the serpentine wiring does not play an inductive role. On the contrary, the inductance will make the higher 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 at least twice of the line width The smaller the interval, the more easily affected by the 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 inductance to improve the anti-interference ability of the circuit.

It is mainly used in some clock signals, such as ciclk and agpclk

1. Impedance matching.

2. Filter inductance.

For some important signals, such as hublink in Intel hub architecture. A total of 13, running 233MHz, must be strictly equal length, in order to eliminate the hidden danger caused by time delay, winding is the only 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 LC filter with distributed parameters in general 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.