[SI-LIST] Re: Fw: Re: The Ground of VNA
- From: steve weir <weirsp@xxxxxxxxxx>
- To: istvan.novak@xxxxxxxxxxxxxxxx, <zhang_kun@xxxxxxxxxx>,"si-list" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 18 May 2004 06:38:28 -0700
Istvan, Zhnagkun, in addition to a balun from MiniCircuits, to avoid stray
coupling effects, a good chunk of common mode ferrite can be helpful. Doug
Smith has written quite a bit about stray coupling messing up measurements,
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 between
>the ground of two ports:
> > > 1. In the VNA, because the instrument is single-ended connections,
>there is finite impedance (Calling Za)between the two ground.
> > > 2. In the DUT, there is impedance unknow (Calling Zb).
> > > Za and Zb are in parallel.
> > >
> > > When Za<Zb, Za is dominant. The measurement result will be influnced by
>the ground loop. For example, there are two differential pair with no ground
>plane. The crosstalk should be measured. Therefore, the ground loop should
>be butted by transformer of 1:1.
> > > When Za>Zb, Zb is dominant. The measurement result will not be influnced
>by the ground loop. For example, in the DUT, there is complete reference
>plane.
> > >
> > > I have found that in different situation, the effect of ground loop in
>VNA is different. In current measurement about crosstalk between
>differential pairs with no reference plane, the influnce could get to above
>20MHz. Now my difficulty is that I could not found one suit 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 individual single-ended connections. When you make
> > > > the connection from a VNA to the DUT with two cables,
> > > > you make a ground loop. The ground loop creates a
> > > > problem only at low frequencies, where the resistance of
> > > > the cable braid dominates the return-path impedance.
> > > > At high frequencies (with most cables above a few MHz),
> > > > the inductance of the cable braid opens the 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 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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