By Signal integrity
Translated by Hualink RF Sunny Li
In front of the introduction of a lot of crosstalk content, including the source and formation of crosstalk, crosstalk types, crosstalk simulation and testing, also introduced some methods to reduce crosstalk, one of the methods to reduce crosstalk is to protect the important signal network.
This additional network is often called a protection line, as shown below:
Can the ground network really protect the signal network?
In particular, the type of ground network shown above (without ground holes).
This article will discuss with you whether this network really needs to be increased.
In general, if there is no protection site design or isolation site structure as shown below:
If the structure of the protected area is as follows:
For this kind of complex problem, we can carry on the simulation analysis through the modeling.
To establish a simple model in ADS, it can be studied qualitatively.
The different structures can be modeled as follows.
When the protection ground is taken into account, the general protection ground cable will be 1W (line width) or 1H (distance from signal to reference layer) away from the signal network to be protected, as shown in the following figure:
The simulation results of near-end and far-end crosstalk are shown as follows:
If the ground at the protected ground is grounded at 1/10 wavelength (equivalent to the ground through hole), its structure is shown in the figure below:
The simulation results of near-end and far-end crosstalk are shown as follows:
If the protective wire is added but not connected to the ground wire, its structure is as shown in the figure below:
The simulation results of near-end and far-end crosstalk are shown as follows:
Without the structure of the protection ground, the distance between the two signal networks will be relatively large, as shown in the figure below:
The simulation results of near-end and far-end crosstalk are shown as follows:
Put the four simulation results together, and the result pair is as shown below,
DB(S(3,1)) means that there is no protection grounding, dB(Guardtrace_2..S(3,1)) indicates that the result contains ground, but there is no ground,
DB(Guardtrace_2gnd..S(3,1)) represents the result of protected ground, grounded at 1/10th wavelength,
DB(Guardtrace_open..S(3,1)) represents the result of no grounding (open circuit) :
From the comparison results, it is clear that crosstalk is greatest when protection ground is added but not connected to GND.
Crosstalk is also greater when a protective ground is added, but if the ground hole is not added at a tenth wavelength, crosstalk is better if it is added.
Of course, if there is enough space, unprotected ground, the result is relatively good, but it will be larger than 1/10th of the wavelength of the ground hole.
The above conclusions are obtained in limited experiments, and are also part of the conclusions and results of recent research on crosstalk. We will share them after the verification board is completed, so the conclusions are for reference only.
If you're interested, you can do more analysis on your own.
