[SI-LIST] Re: Differential line Via - affecting common mode noise

Eric Bogatin teaches classes on this material.  You may find something 
on his web site.

Look for resonances.  They will show up as sharp transitions in S 
parameter magnitude, and they will also show up at non-linear group delay.

Steve.
On 6/10/2011 6:29 AM, Lakshmi Narayanan Sowrirajan, ERS-HCLTech wrote:
> 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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>


-- 
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