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PCB circuit board line what is the role of snake

更新时间:2016-02-21 12:38:00点击次数:2889次
PCB any walk the line in the high frequency signal will of causing the signal delay, serpentine traces the main role is compensation "with a group of related signal line delay is small, some of these is usually no or than the other signals less by another logic series processing; the most typical is the clock line, usually it is not necessary to after any other logic processing and the delay will less than other related signals.
High speed PCB the length is in order to make the signal delay difference is maintained in a range, guarantee the validity of the data read in the same period of the system (the delay difference is more than one clock cycle would be wrong to read the next cycle data), general requirements for delay difference is not more than 1/4 clock cycles. The unit length of the line delay difference is fixed, with delay line width, line length, thickness of copper, the lamellar structure, but the line is too long will increase the distributed capacitance and inductance, so that the quality of the signal, so the clock pin IC generally connected to the RC terminal, but the circuit board line is not an inductance coil, opposite that will make up the harmonic signal inductance in the phase shift caused by the deterioration of the quality of the signal, so the serpentine line spacing is at least two times the width, the rise time of the signal is more susceptible to the effects of distributed capacitance and inductance.
Because different applications with different roles, if snake walk the line appears in the computer board, PCB from the film whose main role to the role of a filter inductor, the anti-interference ability to improve the circuit, computer motherboards in the snake to walk the line, mainly used in some of the clock signals, such as PCIClk, AGPClk. It has two: 1, the impedance matching 2, a filter inductance. Some of the important signal, such as the INTEL HUB architecture in HUBLink, a total of 13, run 233MHz, requirements must be strictly equal, to eliminate the hidden trouble caused by delay, winding is the only solution. Generally speaking, the linewidth of serpentine walk the line line from >=2 times. Slalom PCI board is to adapt to the PCI 33MHzClock line requirements. If in ordinary PCB board is a distributed parameter of the LC filter, but also as the radio antenna inductance coil, short and narrow serpentine traces do fuse and so on.