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), generally requires that the delay difference does not exceed 1/4 clock cycle, and 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 too long a line will increase the distributed capacitance And distributed inductance, so that 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 harmonic phase shift in the rising element of the signal, resulting in deterioration of signal quality, 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 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. Some clock signals, such as CIClk and 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 in total, running at 233MHz. The length must be strictly equal to eliminate the hidden dangers caused by the time lag. Winding is the only solution. Generally speaking, the line spacing of serpentine traces is >=2 times the line width. The snake line on the PCI board is to meet the line length requirements of the PCI33MHzClock. If it is a distributed parameter LC filter in a general ordinary PCB board, it can also be used as the inductance coil of the radio antenna, and the short and narrow serpentine trace can be used as a fuse and so on.
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