[SI-LIST] Re: rise time and bandwidth

First you have to ask why do you care about bandwidth? Frequently you want to  
approximate a physical system and to find an approximate solution.  For 
example, to determine the necessary bandwith for a transmission channel.  For 
these kind of uses it doesn't matter whether it's 0.35/T or 0.3/T; if you're at 
1/10 it won't work, if you're at 10x you have no problem, if you're 0.5 or 2x 
you should be careful and must carefully verify.

As for the case of TDR, you are not trying to approximate a physical system.  
You're trying to judge whether your measurement system is going to deliver the 
benefit of 30 ps edge.  In this case you need a whole system bandwidth of 20 
GHz so that the primary limiting factor is the 30 ps edge itself and not a low 
bandwidth 6 GHz cables.

Regards,
Alfred


Kevin Li <swagguy10@xxxxxxxxx> wrote:

>Hi, experts,
>I am new to this field and I get a question for you guys. I saw a
>formula
>saying BW=0.35/Trise. So for a TDR module with 30ps rise time I should
>get a
>BW of 11.67GHz. Am I correct on this? I saw from a TDR spec that for
>30ps
>rise time, the BW was 20GHz. That confused me.
>
>Thanks.
>Kevin
>
>
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