[SI-LIST] Re: 50 ohm and 130 ohm on the same board

  • From: steve weir <weirsp@xxxxxxxxxx>
  • To: prasadsa@xxxxxxxxxx, <si-list@xxxxxxxxxxxxx>
  • Date: Wed, 02 Jun 2004 11:21:32 -0700

S A, I agree with the poster who questions the 130 ohms in the first=20
place.  Such a high impedance trace is an invitation to EMI.  That sounds a=
=20
lot closer to the odd mode impedance for a differential pair feeding STP=20
and would correspond to 65 - 75 ohms even mode depending on how tightly you=
=20
couple. Before you go defining your board geometry, make sure your=20
requirements are correct.

Steve.
At 08:39 PM 6/2/2004 +0530, saprasad wrote:
>Hello All,
>
>I have a board with 2 sets of signal, the first set of nets need to be at
>50ohm characteristic impedance and the other at 130ohm (single ended).
>This is not practically possible due to manufacturing constrains.
>
>Can you suggest me some technique so i can archive this on the board.
>
>Board details are as fallows:
>No. of Layers: 6
>Stackup: top, ground, signal, signal, power, bottom
>Board thickness is 1.6mm
>
>Regards,
>S A Prasad
>
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>----- Original Message -----
>From: "sghsu55" <sghsu55@xxxxxxxxxxxx>
>To: <John@xxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
>Sent: Wednesday, June 02, 2004 2:54 PM
>Subject: [SI-LIST] Re: Power plane resonace for multi-plane issues
>
>
> >
> > John,
> >
> > We have ever conducted lots of simulation and
> > measurement for the
> > similiar PDS structure as you described. In our
> > experiences, SpeedXP
> > can got quite accurate results with VNA measurement.
> > Especially, the
> > prediction of resonance frequency of PDS plane pair.
> > The results of
> > SpeedXP were slightly greater than measured as well
> > may come from the
> > fringing effect in the edge of plane. I don't have
> > sufficient
> > information to understand your case and simulation
> > setting. However,
> > in my opinion, I don't think that the overlap between
> > VCCP and VCC3_3
> > is a good design.
> >
> > Best regards,
> >
> > Sogo Hsu Ph. D.
> >
> > Foxconn
> >
> >  --- John Lin (aL=A1=A6A=A1P=A1=D1) <John@xxxxxxxxxxxx> ao=A2XTR=A1=B1!G=
>
> > Dear all SI gurus,
> > > one question regarding Power plane resonance.
> > > Currently, I use SpeedXP from Sigrity for simulating
> > > power plane resonance.
> > > The set up is that
> > >            TOP layer :       VCCP
> > > -----  on top layer,
> > >            2nd layer  :      GND, VCC3_3  --
> > > partially overlap both plane  on the second layer
> > >            3rd layer :         GND
> > >           ....
> > >            BOT layer:       VCCP                  --
> > > on bottom layer
> > >
> > >  I inject a current pulse into VCCP at a node on the
> > > top layer. With Fourier transfer for  voltage and
> > > current, and got a plot of plane impedance.   My VNA
> > > measurement shows a resonance at 50 Mhz, but the
> > > simulation show 100Mhz.
> > > I think the mismatch may be among , VCCP,VCC3_3, and
> > > GND plane .  Shall I let VCC3_3 plane float or tie
> > > it to somewhere?
> > >
> > > I know Cadence's PI tool need to specified each
> > > overlapping plane pairs with correct voltage
> > > difference for multi-plane issues.
> > >
> > > I don't know how to take care current injection
> > > issues on Sigrity SpeedXP for multi-planes.
> > >
> > > Does somebody please kindly shed some light on it.
> > >
> > > Thanks,
> > > John
> > >
> >
> >
> >
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