[SI-LIST] Re: Fw: Re: The Ground of VNA
- From: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>
- To: <zhang_kun@xxxxxxxxxx>, "si-list" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 18 May 2004 09:02:24 -0400
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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