[SI-LIST] Re: Fw: Re: The Ground of VNA
- From: "databits" <databits@xxxxxxxxxxxxx>
- To: <weirsp@xxxxxxxxxx>, <istvan.novak@xxxxxxxxxxxxxxxx>,<zhang_kun@xxxxxxxxxx>, "'si-list'" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 18 May 2004 18:03:37 -0500
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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