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

From: abe riazi ([email protected])
Date: Thu May 24 2001 - 13:12:57 PDT

Hi:

Freq = 0.35/Tr is indeed an important bandwidth-rise time formula.

The following relationship between rise time and inverse of frequency,
applicable to numerous high speed buses, is also useful:

Rise Time = 5% to 20% of Clock Period

Regards,

Abe Riazi
ServerWorks

-----Original Message-----
From: Charles Grasso [SMTP:[email protected]]
Sent: Thursday, May 24, 2001 11:39 AM
To: richard hill; [email protected]
Subject: RE: [SI-LIST] : Frequency based on rise time for drivers

The formula refers to the bandwidth associated
with that rise time NOT just a single frequency.
S0 different drivers with different rise times
will exhibit different bandwidths.

Charles Grasso

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of richard hill
Sent: Thursday, May 24, 2001 11:32 AM
To: [email protected]
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.

Rich

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