RE: [SI-LIST] : Frequency based on rise time for drivers

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From: Yibing Tang (ytang@axonphotonics.com)
Date: Thu May 24 2001 - 11:00:47 PDT


Hi, Rich,

The formula is correct.
Freq here doesn't mean bit rate you want to transmit, it means the bandwidth
needed to transmit the signal at certain quality.

For drivers, rise time( edge rate) is not neccessarily to be consistent with
bit rate (your frequency). Even at very low speed, sometimes it requires
very fast rise time. In some situation, faster rise time doesn't mean better
result.

Yibing

-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of richard hill
Sent: 2001 05 24 10:32
To: si-list@silab.eng.sun.com
Subject: [SI-LIST] : Frequency based on rise time for drivers

I have often seen people estimating the frequency of a
driver based on the rise time for the driver using the
formula Freq = .35/Tr (This seems to be true for a
perfect sinusoid). There can be two different
drivers outputing signal at the same frequency but
different edge rates, won't this assumption be
invalid. Some times there is a big difference in the
edge rates of drivers running at the same frequency.
If we use the above formula and estimate the edge rates
using the frequency for the two drivers we will get
similar no.s.

Any comments.

Thanks in advance,
Rich

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