[SI-LIST] Re: Methods to reduce SDD11
- From: Feng Wu <wufengthu@xxxxxxxxx>
- To: sij99@xxxxxxxxx
- Date: Tue, 21 Jan 2014 10:12:59 +0800
Hi Jack
For simulation case, I would propose you to check the simulation setup,
such as material, port and boundary setting, before re-design your
structure.
If it is NOT an urgent case, try to look at the EM field and TDR simulation
result, to locate the problems. and verify the finding by paper calculation
or simulation.
--
B.R.
Feng Wu (Îâ·ã)
-------------
Signal Integrity Engineer
Cisco Shanghai
-------------
2014/1/20 Jack Si <sij99@xxxxxxxxx>
> Hi,
> The S-paramater is obtained from Simulation. It is ensured that, there is
> no split plane underneath and it is continuous Ground plane around the
> trace for 500 mils.
>
>
> As suggested, there may be impedance discontinuity due to
> via(Differential). Please suggest about the placement of the GND via for
> diferential vias and any formula to calculate the impedance for
> (Ground-Signal-Signal-Ground) Via configuration.
>
>
> Thanks,
>
> Jack
>
>
>
>
> On Sunday, January 19, 2014 3:23 PM, Sukumar <sukumarm@xxxxxxxxxxx> wrote:
>
> Hi Jack,
>
> Small correction.
>
> Create clearance under signal pad in ground layer(layer 2) and create
> small ground plane in layer3 under the SIGNAL PAD.
>
>
> Thanks,
> Sukumar,
> SI-Engineer.
>
>
>
>
>
> Sukumar <sukumarm@xxxxxxxxxxx> wrote:
> Hi Jack,
> >
> >If any component pad (foot print) is there, please try following 2 cases,
> >1. Please give the ground clearance under signal pad and simulate.
> >2. Please give the ground clearance under signal pad and create ground
> reference in 3rd layer.
> >
> >Example for case2,
> >Layer1- top
> >Layer2-gnd
> >Layer3- signal or power
> >Layer4- .......
> >
> >Create clearance under signal pad in ground layer(layer 2) and create
> small ground plane under the signal in layer3.
> >
> >Feel free to contact me.
> >If possible, let me know the signal pad length and width.
> >
> >
> >Thanks,
> >Sukumar
> >SI Engineer.
> >
> >
> >
> >
> >
> >
> >
> >Jack Si <sij99@xxxxxxxxx> wrote:
> >Hi Experts,
> >>When i evaluate a Differential S-parameter of a 100 ohm differential
> trace (4 mil trace width and spacing of 6.35mils) which travels through
> microstrip length of 50 mils and stripline of 2500 mils with two vias
> without any stub, I found that the the value of SDD11 is more than the
> expected at the frequency of 5 GHz (around -10 dB). The differential via is
> of 8 mil drill and 20 mils pad with the spacing between the via is 25 mils.
> The impedance of single via is has the impedance of 49ohm.
> >>
> >>Please suggest the method to reduce SDD11.
> >>
> >>Thanks,
> >>
> >>Jack
> >>
> >>
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