[SI-LIST] Re: rise time and bandwidth
- From: Alfred Lee <alfred1520list@xxxxxxxxx>
- To: Kevin Li <swagguy10@xxxxxxxxx>,si-list@xxxxxxxxxxxxx
- Date: Tue, 13 Sep 2011 21:40:13 -0700
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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