[SI-LIST] Re: 2 questions about TRL cal
- From: "Luciano Boglione" <l.boglione@xxxxxxxx>
- To: "'Jim Nadolny'" <jim.nadolny@xxxxxxxxxx>, "'Mick zhou'" <mick.zhou@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Mon, 8 Aug 2011 10:52:57 -0400
Mick,
When you enter the delay, the reference planes are set at the edges of the
delay line (i.e. at the probe tips); if you enter a 0 delay, the reference
planes are set at length/2 of the delay line (mid point).
Take care,
Luciano
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Jim Nadolny
Sent: Monday, August 08, 2011 10:45 AM
To: Mick zhou; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: 2 questions about TRL cal
Hey Mick -
My 2 cents...
On the delays - I always measure the delay differences in the line standards
first, then specify the delays in the cal kit definition. The result has
been pretty good success with the behavior of the extracted models. 4 or 5
years ago I was starting to dig into all this and was told (by an industry
colleague) that the Agilent code does not use the delay numbers...so just
use 0 ps. When I asked Agilent about that practice they sort of looked at
me like I had 3 heads - yes you need to specify the delay so that is what I
do. To be honest - I can't really answer your question though, just my
experience.
On the overlap - I use the overlap as a safety measure to cover variations
in substrate performance. Gives me margin when dealing with batch to batch
variations in FR-406. Having the overlap also allows you a range of
frequencies that you can use to intelligently select as a transition
frequency. The selection of the transition frequency can impact the "steps"
in the measured RL that is characteristic of TRL/M calibration.
jn
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Mick zhou
Sent: Monday, August 08, 2011 10:19 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] 2 questions about TRL cal
All,
There are two simple questions about TRL calibration that papers/app notes
are not very clear about.
1. Is it necessary to enter delays of lines?
The entries are available in the GUI. I have seen people think the
delays are not necessary and use 0ps for all. The argument is: the delay is
determined as part of the process. According to the theory, S12 and
exp(-gamma*l) are determined to a sign ambiguity. Extra infomation such as
delay is needed to uniquely decide the sign (therefore the phase). However,
delay may not be a problem for engineers who don't care phases. because they
don't "see" the difference by looking at magnitudes only. But this could be
dangerous if the models without correct phases are used in time domain
simulations, the delays could be wrong unless you are lucky the phases are
always within 20-160 degrees (8:1 case).
2. Is overlap of frequencies necessary in case of multi-lines? Again it is
related to accuracy of phases. Some believe overlaps can improve phase
accuracy. Some don't believe so. The instrument picks up either the last
(unguided cal) or the prority set by Smartcal (guided cal). So how the phase
accuracy is improved?
Thanks
Mick
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