[SI-LIST] Re: A question for the instrument guys on TDR and TDT
- From: steve weir <weirsi@xxxxxxxxxx>
- To: Chris.Cheng@xxxxxxxxxxxx
- Date: Mon, 06 Nov 2006 22:02:07 -0800
Chris, the VNA is up to the task. TDA Systems, now Tektronix put out
some nice papers in I believe 2003 / 2004 on using VNAs for TDR, and
TDR as a poor man's VNA. For signals there are a number of cases
where either works quite well. Designing the probe access and
launches is the tricky part. The same applies for the TDR. It is
pretty easy and all too common to see suboptimal launches mask away
what is really going on whether using a VNA, or a TDR/TDT. Each has
its place. I really prefer VNAs for power systems because of the
broad frequency range, and wide dynamic range. I have the luxury of
access to both tools.
Best Regards,
Steve.
At 08:08 PM 11/6/2006, Chris Cheng wrote:
>I sure would like to see the VNA that can do real system channel =
>measurements at 100db after fixture and cabling.
>On the other hand, even at 40/60db range, a sampling scope may be good =
>enough for a channel measurement up to a few GHz. Not a bad alternative.
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx
>[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Istvan Novak
>Sent: Monday, November 06, 2006 7:50 PM
>To: Chris Cheng
>Cc: istvan.novak@xxxxxxx; si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: A question for the instrument guys on TDR and TDT
>
>
>The 'why not' is an interesting question, and you may get several=20
>different answers,
>dependent on priorities. My answer is that a scope is OK for low=20
>dynamic range
>or low-frequency measurements, in those applications it is cheaper than=20
>VNA and
>works fine. On the other hand, VNAs can achieve 100+ dB dynamic range=20
>easily;
>to get that in a scope, the effective number of bits would need to be=20
>16+, not
>available today on fast scopes.=20
>
>If milliohms need to be measured, VNA is hard to beat. For
>tens and hundreds of milliohms or higher, scope would be acceptable.
>
>Regards,
>
>Istvan
>
>
>Chris Cheng wrote:
>
> >I would agree. However, the question is not whether the scope is =
>capable =3D
> >of doing it but why not ? The controls are almost there (for the =3D
> >TDR/TDT) and de-embedding is a simple step of shifting the reference =
>=3D
> >plane or simple post processing FIR filter (something advance sampling =
>=3D
> >scope can already do). A $40K+ VNA vs. a free firmware upgrade on the =
>=3D
> >sample scope. Which one will you choose !?
> >
> >-----Original Message-----
> >From: Istvan Novak [mailto:istvan.novak@xxxxxxxxxxx]
> >Sent: Monday, November 06, 2006 5:31 PM
> >To: Chris Cheng
> >Cc: si-list@xxxxxxxxxxxxx
> >Subject: Re: [SI-LIST] A question for the instrument guys on TDR and =
>TDT
> >
> >
> >Chris,
> >
> >The answer is yes (as long as the network is 'sufficiently' linear). =
>=3D20
> >The finite rise time
> >shows up as filtering, what happens in all simulations or =
>measurements=3D20
> >anyway,
> >even if we neglect the effect of risetime. If you need the impedance =
>of =3D
> >
> >a power
> >distribution network, the quantization of the receiving instrument =
>will=3D20
> >set the noise floor.
> >
> >Regards,
> >
> >Istvan Novak
> >SUN Microsystems
> >
> >Chris Cheng wrote:
> >
> > =20
> >
> >>I can understand the merit of a step response and direct read out of =
>=3D
> >> =20
> >>
> >=3D3D
> > =20
> >
> >>impedance profile.
> >>Will it be easy to also include a mode with a sharp pulse instead of =
>=3D
> >> =20
> >>
> >=3D3D
> > =20
> >
> >>step for an impulse response ? If you have a circuit to generate a =
>35ps =3D
> >> =20
> >>
> >=3D3D
> > =20
> >
> >>step, can you use it to generate a 35ps pulse also ? I think there are =
>=3D
> >> =20
> >>
> >=3D3D
> > =20
> >
> >>steps you can do to convert one to the other but a direct impulse =
>=3D3D
> >>response is just too good to pass up.
> >>Network analyzer on the cheap.
> >>Thanks in advanced,
> >>Chris
> >>
> >>
> >>=3D20
> >>
> >> =20
> >>
> >
> > =20
> >
>
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