[SI-LIST] SSN and Crosstalk in Package
- From: Zhangkun <zhang_kun@xxxxxxxxxx>
- To: si-list <si-list@xxxxxxxxxxxxx>
- Date: Fri, 15 Apr 2005 16:48:36 +0800
Dear all
Recently, I was simulating SSN in package. I found out that in the "SSN" noise,
there are two parts:
1. The noise because of the inductance of power or ground net.
2. The crosstalk between signals.
Moreover, I noticed that the second part is much larger than the first one. The
verification method is to simulate twice:
1.Regular simulation.
2.Simulation with perfect power supply. Therefore the inductance of power
or ground net is eliminated.
Comparing these two SSN simulaiton results, I notice that the difference is not
great. Therefore, I concluded that the main source of "SSN" is the crosstalk in
package.
Let the above conclusion be correct. I think that the SSN would be not very
critical. My explanation is following. Based on the "SSN" waveform, it is clear
that the crosstalk is mainly inductive and the capacitive coupling is small.
When the inductive and capacitive coupling is not equal, the farend crosstalk
is very large. The nearend crosstalk would be very small for the trace in
package is very short.
Now let us consider several SSN situation. There are N IO ports in the IC.
1.(N-1) net is output and aggressive. Victim net is output and quiet.
Because the crosstalk is inductive, there would be great "SSN" in the
victim net. However, the "SSN" is of high frequency. When the "SSN" is
transfered along the transmission line, it would be damped and would not damage
the signal integrity of victim net.
2.(N-1) net is output and agressive. Victim net is input and quiet.
Because the nearend crosstalk is small, there would be no great damage
for the input net.
3.(N-1) net is input and aggressive. One net is input/outpu, quiet, and
victim.
Normally, the risetime and falltime at input buffer is large for the
damp of transmission line or loading effect. Therefore, there would be no
critical crosstalk.
At last, there would be no critical "SSN" problem if the crosstalk in package
is dominating.
The above is my viewpoint about SSN in package. Any comment is welcome. The
basic is that crosstalk in package is much larger that the noise because of
inductance of power supply system.
Best Regards
Zhangkun
2005.4.15
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