[SI-LIST] Re: Methods to reduce SDD11
- From: Jack Si <sij99@xxxxxxxxx>
- To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Sun, 19 Jan 2014 19:44:21 -0800 (PST)
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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