Reproduction forbidden without Fibocom Wireless Inc. written authorization - All Rights Reserved.
L850-GL Hardware User Manual Page 32 of 54
It shall avoid the discontinuous reference ground, such as segment and space;
When the differential signal lines go through different layers, the via hole of grounding signal
should be in close to that of signal, and generally, each pair of signals require 1-3 grounding
signal via holes and the lines shall never cross the segment of plane;
Try to avoid bended lines and avoid introducing common-mode noise in the system, which will
influence the signal integrity and EMI of difference pair. As shown in Figure 3-12, the bending
angle of all lines should be equal or greater than 135
°
, the spacing between difference pair
lines should be larger than 20mil, and the line caused by bending should be greater than 1.5
times line width at least. When a serpentine line is used for length match with another line, the
bended length of each segment shall be at least 3 times the line width (
≥
3W). The largest
spacing between the bended part of the serpentine line and another one of the differential lines
must be less than 2 times the spacing of normal differential lines (S1<2S);
Figure 3-12 Requirement of PCIe Line
The difference in length of two data lines in difference pair should be within 5mil, and the length
match is required for all parts. When the length match is conducted for the differential lines, the
designed position of correct match should be close to that of incorrect match, as shown in Figure
3-13. However, there is no specific requirements for the length match of transmit pair and receiving
pair, that is, the length match is only required in the internal differential lines rather than between
different difference pairs. The length match should be close to the signal pin and pass the small-angle
bending design.