[SI-LIST] Re: A question for the instrument guys on TDR and TDT
- From: "Chris Cheng" <Chris.Cheng@xxxxxxxxxxxx>
- Date: Mon, 6 Nov 2006 20:08:06 -0800
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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=20
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