[ibis-macro] Re: On impulse and step responses.
- From: Gregory R Edlund <gedlund@xxxxxxxxxx>
- To: msteinb@xxxxxxxxxx
- Date: Thu, 20 Jun 2013 14:21:20 -0500
Mike,
I think it's a valid question. My book on Linear Systems is heavy on math
and light on applications. There is no mention of physical units, which is
a reasonable topic for any physical discussion. As a user, I'm trying to
understand things at a deeper level so I can know when to trust my
simulations and when not to.
Sadly, our professors rarely gave us enough time to absorb the material we
were supposed to be learning. I remember feeling afraid to ask questions
that I thought everyone else knew. Once you watch a professor tear a
classmate to shreds, it makes you think twice about opening your own mouth.
Now that the diploma is hanging on the wall, though, I feel a little more
bold about revealing the shortcomings in my own knowledge. It's the only
way to learn.
I've always appreciated your willingness to explain. I see this reflector
as a virtual community where everyone can feel welcome. I know I've asked
a lot of newbie questions over the years, and I'm grateful to the folks who
took the time to answer. Let's keep the communication going. If someone
thinks a certain topic is a waste of time, hitting the delete key only
takes a second.
Greg
p.s. In case anyone is interested, here's a story featuring someone who
thinks LaPlace transforms have no physical meaning. It's a great
illustration of the state of higher education. Since I just helped two
kids through a VERY expensive university education, I'm sensitized to the
topic of value.
http://www.physicsforums.com/showthread.php?t=155709
Greg Edlund
Senior Engineer
Signal Integrity and System Timing
IBM Systems & Technology Group
3605 Hwy. 52 N Bldg 050-3
Rochester, MN 55901
From: Mike Steinberger <msteinb@xxxxxxxxxx>
To: ibis-macro@xxxxxxxxxxxxx
Date: 06/20/2013 12:35 PM
Subject: [ibis-macro] Re: On impulse and step responses.
Sent by: ibis-macro-bounce@xxxxxxxxxxxxx
Greg-
The math is truly still the math, but it also has to be all the math.
If you want to use a narrow pulse of whatever shape, that's fine; however
it is essential that the pulse always has unit area (volts * seconds).
Therefore, as your pulse gets narrower and narrower, its amplitude has to
get greater and greater. In fact, the Dirac delta function has, by
definition, unit area, in that it's defined as the limit of your narrow
pulse (with unit area) as the width of the pulse goes to zero.
In the sampled data World, we don't actually take the width of the pulse to
zero. Rather, we leave it one sample wide, as being the narrowest pulse we
can generate in that domain. The sampled data equivalent of the (continuous
time domain) Dirac delta function therefore has a width of one sample and
an amplitude of one over the sample interval.
People, these are fundamental concepts that each of us should have learned
in college. Do they really require discussion on a public reflector?
Cheers,
Mike Steinberger
On 06/20/2013 11:54 AM, Gregory R Edlund wrote:
The Math is the Math. Do not question it!
Seriously, though. The other way to define an impulse response is
the response of a network to a very narrow triangular or Gaussian
stimulus (Dirac delta function), right? This waveform certainly has
unit of Volts. The math must necessarily be different in these two
cases for it to be physically meaningful.
Greg Edlund
Senior Engineer
Signal Integrity and System Timing
IBM Systems & Technology Group
3605 Hwy. 52 N Bldg 050-3
Rochester, MN 55901
Inactive
hide details for David Banas ---06/20/2013 09:52:18
AM---Hi
all, In our work, we often take as a priori that the
impulDavid Banas ---06/20/2013 09:52:18 AM---Hi all, In our work, we
often take as a priori that the impulse response is the time
derivative of t
From: David Banas <DBanas@xxxxxxxxxx>
To: "ibis-macro@xxxxxxxxxxxxx" <ibis-macro@xxxxxxxxxxxxx>
Date: 06/20/2013 09:52 AM
Subject: [ibis-macro] On impulse and step responses.
Sent by: ibis-macro-bounce@xxxxxxxxxxxxx
Hi all,
In our work, we often take as a priori that the impulse response is
the time derivative of the step response. As I puzzle over this
further, I realize that I’m stumped by something very fundamental,
which is this:
A quantity, which is the time derivative of some other quantity,
cannot have the same units as that other quantity. And, yet, when we
discuss/measure/simulate either a step response or an impulse
response, we expect to be talking about / measuring / viewing a
voltage as a function of time, in both cases! How can this be?
Thanks,
-db
Confidentiality Notice.
This message may contain information that is confidential or
otherwise protected from disclosure. If you are not the intended
recipient, you are hereby notified that any use, disclosure,
dissemination, distribution, or copying of this message, or any
attachments, is strictly prohibited. If you have received this
message in error, please advise the sender by reply e-mail, and
delete the message and any attachments. Thank you.
Other related posts:
