[SI-LIST] Re: Differential line Via - affecting common mode noise
- From: "Lakshmi Narayanan Sowrirajan, ERS-HCLTech" <lakshminarayanans@xxxxxxx>
- To: "istvan.novak@xxxxxxx" <istvan.novak@xxxxxxx>
- Date: Fri, 10 Jun 2011 18:59:17 +0530
Hi,
I have generated mixed mode S parameter for the entire structure
excluding the DRV and terminations as below.
1) Port 1 ---- brkout---via---8inch routing-----via----conn---4inch
routing----Port 2
2) Port 1 ----- brkout--- 8inch routing-----conn---4inch routing---- Port 2
When I compared the SDC(1,2) & SCD(1,2) plots for both cases, they are closely
matching and there is no major visible changes in the plots. But, while
compared the SCC(1,2) the waveforms are closely matching in all regions, except
in 2.5G to 3G range there is a small difference in the plot. Where the dip in
case 0 reaches -41db and case 1 reaches -37db. Whether we need to infer this as
Case 0 has more insertion loss for common mode noise from Port 1 to port 2 when
compared to Case 1 or Case 0 is more susceptible to Common mode noise in the
2.5G to 3G range when compared to Case 1.
Please clarify on the interpretation of SCC(1,2) plot for both cases. Please
direct me to a good article/paper/book to understand more about understanding
about mixed mode s-parameter interpretations.
Thanks & Regards
Lakshminarayanan. S
9840250902
-----Original Message-----
From: Istvan Novak [mailto:istvan.novak@xxxxxxx]
Sent: Thursday, June 09, 2011 6:30 PM
To: Lakshmi Narayanan Sowrirajan, ERS-HCLTech
Cc: steve weir; si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: Differential line Via - affecting common mode noise
Hi Lakshmi,
When you say 'less common mode noise', I assume you refer to time-domain
common mode voltage with a given data rate and data pattern excitation,
correct?
In a typical channel with a connector and multiple traces, chances are
that the mode conversion is frequency dependent. The peaks and minima
of the mode conversion very well may depend on delays among
discontinuities as well, so when you change the length, or the
reflection, or the attenuation, it may shift the modal conversion curves
left or right and up/down. If you have not done so yet, it would be very
useful to compare the end-to-end S parameters for the two cases in the
frequency domain to see if they make sense to you.
Regards,
Istvan Novak
Oracle
On 6/9/2011 7:28 AM, Lakshmi Narayanan Sowrirajan, ERS-HCLTech wrote:
> Hi Steve,
>
> Thanks for the reply, please find the details as below.
>
> 1) DRV---brkout---via---8inch routing-----via----conn---4inch
> routing----termination (x_p,x_n)
>
> 2) DRV---brkout--- 8inch routing-----conn---4inch routing----termination
> (x_p,x_n)
>
> Signal is probed near termination and we see less common mode noise in case
> 1, where we have via (modeled in HFSS as s4p)
>
> Common mode noise = (v(x_p)+V(x_n))/2
>
> Thanks& Regards
> Lakshminarayanan. S
> 9840250902
>
>
> -----Original Message-----
> From: steve weir [mailto:weirsi@xxxxxxxxxx]
> Sent: Thursday, June 09, 2011 4:32 PM
> To: Lakshmi Narayanan Sowrirajan, ERS-HCLTech
> Cc: si-list@xxxxxxxxxxxxx
> Subject: Re: [SI-LIST] Differential line Via - affecting common mode noise
>
> Where and how are you measuring your CM noise? Virtually all vias
> impose insertion loss. Non-transparent vias insert reactive
> discontinuities.
>
> Steve
> On 6/8/2011 11:49 PM, Lakshmi Narayanan Sowrirajan, ERS-HCLTech wrote:
>> Hi Experts,
>> How the via improve or degrade the differential lines
>> common mode noise and performance as I am getting more common mode noise for
>> a case where I don't have any via. If I include a transition via (modeled in
>> HFSS - s4p model) the common mode noise is getting reduced. Please direct me
>> to a good article/paper/book to understand the theory behind this.
>>
>> Thanks& Regards
>> Lakshminarayanan. S
>>
>>
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