[SI-LIST] Re: Fw: Re: The Ground of VNA
- From: steve weir <weirsp@xxxxxxxxxx>
- To: databits@xxxxxxxxxxxxx, <istvan.novak@xxxxxxxxxxxxxxxx>,<zhang_kun@xxxxxxxxxx>, "'si-list'" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 18 May 2004 16:52:25 -0700
You bet! This particularly applies to parallel shunt measurements such as
in a PDS. There is all kinds of fun to be had if one does not both set-up
and properly account for the effects of the series connections.
Regards,
Steve.
At 06:03 PM 5/18/2004 -0500, databits wrote:
>The other piece that seems to get forgotten is that placing the =
>instrument
>"grounds" on both sides of a lossy return path (all return paths are =
>lossy
>:) ) can effect how measurements relate to simulations relative to the
>actual circuit performance ... (This includes models from measurements,
>right Dima).
>
>Correlation requires modeling what you measure... and measuring what you
>model... then the $64,000 question... Do the measurements and the =
>models
>(that hopefully match) have any relation to actual system performance. =
>Oh
>the joys of simulation and test...
>
>ap
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
>On
>Behalf Of steve weir
>Sent: Tuesday, May 18, 2004 8:38 AM
>To: istvan.novak@xxxxxxxxxxxxxxxx; zhang_kun@xxxxxxxxxx; si-list
>Subject: [SI-LIST] Re: Fw: Re: The Ground of VNA
>
>
>Istvan, Zhnagkun, in addition to a balun from MiniCircuits, to avoid =
>stray=20
>coupling effects, a good chunk of common mode ferrite can be helpful. =
>Doug=20
>Smith has written quite a bit about stray coupling messing up =
>measurements,=20
>how to detect it is happening, and how to fix it.
>
>Regards,
>
>
>Steve.
>At 09:02 AM 5/18/2004 -0400, Istvan NOVAK wrote:
> >Dear Zhangkun,
> >
> >OK; not having a ground plane for differential pairs clearly falls into =
>
> >the category when the ground loop of the VNA will influence your result =
>
> >over a wide band.
> >
> >You could try balun transformers to transform the
> >differential connections to single ended. MiniCircuits
> >has a wide range of transformers for all frequency
> >ranges.
> >
> >Best regards,
> >
> >Istvan
> >
> >
> >----- Original Message -----
> >From: "Zhangkun" <zhang_kun@xxxxxxxxxx>
> >To: "si-list" <si-list@xxxxxxxxxxxxx>
> >Sent: Tuesday, May 18, 2004 8:00 AM
> >Subject: [SI-LIST] Fw: Re: The Ground of VNA
> >
> >
> > >
> > > ----- Original Message -----
> > > From: "Zhangkun" <zhang_kun@xxxxxxxxxx>
> > > To: <istvan.novak@xxxxxxxxxxxxxxxx>
> > > Sent: Tuesday, May 18, 2004 7:52 PM
> > > Subject: Re: [SI-LIST] Re: The Ground of VNA
> > >
> > >
> > > > Dear Istvan
> > > >
> > > > The following is my understand about the ground loop in VNA.
> > > >
> > > > When measurement is done by means of VNA, there is two impedance=20
> > > > between
> >the ground of two ports:
> > > > 1. In the VNA, because the instrument is single-ended=20
> > > > connections,
> >there is finite impedance (Calling Za)between the two ground.
> > > > 2. In the DUT, there is impedance unknow (Calling Zb). Za and=20
> > > > Zb are in parallel.
> > > >
> > > > When Za<Zb, Za is dominant. The measurement result will be=20
> > > > influnced by
> >the ground loop. For example, there are two differential pair with no=20
> >ground plane. The crosstalk should be measured. Therefore, the ground=20
> >loop should be butted by transformer of 1:1.
> > > > When Za>Zb, Zb is dominant. The measurement result will not be=20
> > > > influnced
> >by the ground loop. For example, in the DUT, there is complete=20
> >reference plane.
> > > >
> > > > I have found that in different situation, the effect of ground=20
> > > > loop in
> >VNA is different. In current measurement about crosstalk between=20
> >differential pairs with no reference plane, the influnce could get to=20
> >above 20MHz. Now my difficulty is that I could not found one suit=20
> >transformer of 1:1 to break the ground loop.
> > > >
> > > > Best Regards
> > > >
> > > > Zhangkun
> > > > 2004.5.18
> > > > ----- Original Message -----
> > > > From: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>
> > > > To: <zhang_kun@xxxxxxxxxx>; "si-list" <si-list@xxxxxxxxxxxxx>
> > > > Sent: Tuesday, May 18, 2004 7:18 PM
> > > > Subject: [SI-LIST] Re: The Ground of VNA
> > > >
> > > >
> > > > > Dear Zhangkun,
> > > > >
> > > > > High-frequency instruments use single-ended connections; most of =
>
> > > > > the differential inputs and outputs are also formed of=20
> > > > > individual single-ended connections. When you make the=20
> > > > > connection from a VNA to the DUT with two cables, you make a=20
> > > > > ground loop. The ground loop creates a problem only at low=20
> > > > > frequencies, where the resistance of the cable braid dominates=20
> > > > > the return-path impedance. At high frequencies (with most cables =
>
> > > > > above a few MHz), the inductance of the cable braid opens the=20
> > > > > ground loop so much so that you can cross-connect the cables by
> > > > > connecting the hot side of cable1 to the ground side of
> > > > > cable2 and hot side of cable2 to the ground side of cable1
> > > > > and under some circumstances you will hardly notice the
> > > > > difference in the response.
> > > > >
> > > > > Regards,
> > > > >
> > > > > Istvan Novak
> > > > > SUN Microsystems
> > > > >
> > > > >
> > > > > ----- Original Message -----
> > > > > From: "Zhangkun" <zhang_kun@xxxxxxxxxx>
> > > > > To: "si-list" <si-list@xxxxxxxxxxxxx>
> > > > > Sent: Tuesday, May 18, 2004 5:12 AM
> > > > > Subject: [SI-LIST] The Ground of VNA
> > > > >
> > > > >
> > > > > > Dear All
> > > > > > Could you tell me the details about the ground of VNA? From=20
> > > > > > the
> > > > > experiment, I could find out that the ground of two ports of VNA =
>
> > > > > are connected. However, I do not know the detail.
> > > > > >
> > > > > > This is critical for some kind of analysis. For example, there =
>
> > > > > > is no
> > > > > ground plane.
> > > > > >
> > > > > > Best Regards
> > > > > >
> > > > > > Zhangkun
> > > > > > 2004.5.18
> > > > > >
> > > > > >
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