tramp,
Why do you want the impulse response?
With iFFT, you can never get rid of the negative-time tail of an impulse
response except for some ideal examples. Frequency-domain windowing will
smoothen the ripples, but will not remove the negative-time part.
Zeroing-out negative-time part can cause more problems than it solves. For
one, it will affect your dc value. For another, your S-parameters could
have become non-passive as a result.
I will not recommend enforcing causality through Hilbert transform, because
you have no control over the accuracy. In other words, the
causally-corrected frequency response can differ from the original response
than what is acceptable, and there is no easy way to control the accuracy.
You wrote that causality of the s-param is good enough. I am curious how
did you find this. Given the causality is already good enough, it is better
to stick to the same S-parameters.
lal
On Thu, Jun 11, 2020 at 11:44 AM Tramp <farhilltramper@xxxxxxxxx> wrote:
Hi Aldo,
I'm eager to read the paper you mentioned. Could you send me a copy? Or
other helpful info if your paper cannot be shared yet.
Best Regards,
Tramp
On Thu, Jun 11, 2020 at 3:18 PM Morales, Aldo W <awm2@xxxxxxx> wrote:
Hi All:there
This is not a problem of the ifft, not fmax. It is a sampling problem as
well as the way your data is being processed. A lot of the papers out
are wrong. You can contact me to discuss this is in detail. We have_____________________________________________________________________________________________
submitted a paper on that regard.
Cheers,
Aldo
DUT.
Aldo W. Morales, Ph.D. IEEE Senior Member
IEEE Consumer Electronics Society 15-16 Distinguished Lecturer
Co-Director, Center of Excellence in Signal Integrity
<http://www.hbg.psu.edu/csi>
https://harrisburg.psu.edu/center-for-signal-integrity
Professor of Electrical Engineering
Penn State Harrisburg
777 West Harrisburg Pike
Middletown, PA 17057
U.S.A.
Phone: (717)-948-6379
Fax: (717)-948-6352
________________________________
From: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx> on
behalf of Thomas Beneken <thomas.beneken@xxxxxxxxxxx>
Sent: Thursday, June 11, 2020 10:01 AM
To: si-list@xxxxxxxxxxxxx <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Re: noncausal ripples in impulse response
Hello Tramp,
it's written in the fine print coming with the fft/ifft transformations
that they are valid for repetitive signals, only. The ripple you observe
before t=0 is just a late response to the preceding step pulse. To avoid
that give more time for the responses to the preceding step to settle.
Smaller frequency steps do help.
Another source of ripple is that you just cut off the frequency response
of your DUT at maximum frequency. If the response of your DUT has not
levelled out to zero at maximum frequency there will be ripple in the
time domain. It's like applying a high order low pass filter. The remedy
for this is to have a nice roll off for the frequency response of the
thereafter
Thank you!
Thomas
Am 11.06.2020 um 13:43 schrieb Tramp:
Hi experts,doesnt
When obtaining the impulse response using ifft, often the generated ir
(impulse response) shows a bit of ripple&noise before t=0. I did some
experiments and here is the observation:
1. Increasing fmax, which is the max freq for the IL extrapolation,
help reduce the ripple.sparam
2. Changing delta-f shows no avail as well.
3. Although the causality of the sparam is already good enough, still I
tried composing a 'causal' sparam by replacing the imag part of the
w/ the Hilbert transform of the real part. Unfortunately, the
zero-outproduced ir is a complete mess. What went wrong here?
I read from some literatures where the authors said they simply
https://nam01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.freelists.org%2Fwebpage%2Fsi-list&dataall the ripples before t=0. Is this a recommended approach? Are there
better solutions to obtain a genuine ir?
Best Regards,
Tramp
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