[SI-LIST] Re: 3dB or Knee Frequency
- From: "Dagostino, Tom" <tom_dagostino@xxxxxxxxxxx>
- To: "'zabinski.patrick@xxxxxxxx'" <zabinski.patrick@xxxxxxxx>,si-list@xxxxxxxxxxxxx
- Date: Thu, 13 Jun 2002 11:38:21 -0700
If you put a step into a systems that has a finite risetime the resultant
risetime will be degraded. This shows how much you can expect.
Step Tr System Tr Resultant Tr
1 10 10.04988
1 9 9.05539
1 8 8.06226
1 7 7.07107
1 6 6.08276
1 5 5.09902
1 4 4.12311
1 3 3.16228
1 2 2.23607
1 1 1.41421
1 0.9 1.34536
1 0.8 1.28062
1 0.7 1.22066
1 0.6 1.16619
1 0.5 1.11803
1 0.4 1.07703
1 0.3 1.04403
1 0.2 1.01980
1 0.1 1.00499
1 0.09 1.00404
1 0.08 1.00319
1 0.07 1.00245
1 0.06 1.00180
1 0.05 1.00125
1 0.04 1.00080
1 0.03 1.00045
1 0.02 1.00020
1 0.01 1.00005
Tom Dagostino
Modeling Manager
Mentor Graphics Corp.
SAS
tom_dagostino@xxxxxxxxxx
503-685-1613
-----Original Message-----
From: Zabinski, Patrick J. [mailto:zabinski.patrick@xxxxxxxx]
Sent: Thursday, June 13, 2002 11:10 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: 3dB or Knee Frequency
All:
Has anyone performed an analysis based on something like:
* determine power spectral density from a random data pattern
with a specific data rate and edge rate to determine
the frequency which captures 99% (or some other limit)
of the total energy?
- or -
* look at the analog waveforms through some form of
metric and determine what frequencies are nessary
to maintain an edge rate within some level of
tolerance?
The discussion of "3 dB" and "knee" frequencies is interesting,
but I guess I'm trying to see how these frequencies actually
pertain to the digital (yet analog) signal of interest. (???)
Pat
>
>
> Hi All,
>
> When we talk about high edge rate signals, we talk about two
> terms namely
> 1> 3 dB frequency, which is related to the edge rate as approximately
> 0.35/Tr
> and
> 2> Knee frequency (mentioned in Howard Johnson's famous book and many
> SI-list
> mails) which is given as 0.5/Tr.
>
> Questions:
> 1> What is Knee frequency? Does it relate to the highest harmonic
> 1> present
> in
> the signal with significant energy? How relevant it is in
> High speed board
> design as against 3dB frequency?
>
> 2> To determine the decoupling caps, we have to determine
> the highest
> significant frequency involved in the switching signals. Now
> the question is
> should we consider the 3dB frequency ( mentioned in High
> Speed Digital
> Design by Stephen Hall) or the knee frequency ( in Howards
> Johnson's Black
> MAgic) as the best approximation? Let us consider
> Tr=1ns. Then we have
> 3dB
> frequency = 350Mhz and Knee frequency = 500 Mhz.
>
> Regards,
> Anand.
>
>
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