[SI-LIST] Re: SSN and Crosstalk in Package
- From: steve weir <weirsi@xxxxxxxxxx>
- To: zhang_kun@xxxxxxxxxx, si-list <si-list@xxxxxxxxxxxxx>
- Date: Fri, 15 Apr 2005 04:55:18 -0700
Zhangkun, your results are very unexpected. For most packages the common
return inductance is dominant over line to line coupling. I think there
is a flaw in your method. Can you explain further how in your simulation
you eliminated the parasitics of the power distribution network but
retained the signal return parasitics?
I think we should wait to discuss your observations and conclusions until
we are satisfied that your model is valid. Respectfully, right now I have
grave doubts about your model.
Regards,
Steve
At 04:48 PM 4/15/2005 +0800, Zhangkun wrote:
>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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