[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 
different answers,
dependent on priorities.  My answer is that a scope is OK for low 
dynamic range
or low-frequency measurements, in those applications it is cheaper than 
VNA and
works fine.  On the other hand, VNAs can achieve 100+ dB dynamic range 
easily;
to get that in a scope, the effective number of bits would need to be 
16+, not
available today on fast scopes. 

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 =
>of doing it but why not ?  The controls are almost there (for the =
>TDR/TDT) and de-embedding is a simple step of shifting the reference =
>plane or simple post processing FIR filter (something advance sampling =
>scope can already do). A $40K+ VNA vs. a free firmware upgrade on the =
>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). =20
>The finite rise time
>shows up as filtering, what happens in all simulations or measurements=20
>anyway,
>even if we neglect the effect of risetime.  If you need the impedance of =
>
>a power
>distribution network, the quantization of the receiving instrument will=20
>set the noise floor.
>
>Regards,
>
>Istvan Novak
>SUN Microsystems
>
>Chris Cheng wrote:
>
>  
>
>>I can understand the merit of a step response and direct read out of =
>>    
>>
>=3D
>  
>
>>impedance profile.
>>Will it be easy to also include a mode with a sharp pulse instead of =
>>    
>>
>=3D
>  
>
>>step for an impulse response ? If you have a circuit to generate a 35ps =
>>    
>>
>=3D
>  
>
>>step, can you use it to generate a 35ps pulse also ? I think there are =
>>    
>>
>=3D
>  
>
>>steps you can do to convert one to the other but a direct impulse =3D
>>response is just too good to pass up.
>>Network analyzer on the cheap.
>>Thanks in advanced,
>>Chris
>>
>>
>>=20
>>
>>    
>>
>
>  
>

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