[SI-LIST] Re: 2 questions about TRL cal
- From: "Luciano Boglione" <l.boglione@xxxxxxxx>
- To: "'Mick zhou'" <mick.zhou@xxxxxxxxx>
- Date: Wed, 10 Aug 2011 12:23:18 -0400
Mick,
Overlapping lines are handled by the instrument and the way it is handled,
may depend on the instrument. In theory, one should get equivalent
calibrations when repeating the cal in the overlapping frequency range with
2 delay lines. However, what the instrument actually does, may depend on how
the instrument is set up. Unfortunately, this makes the answer
instrument-dependent. I used an Agilent PNA model E8364B with a Cascade ISS
101-190 calkit; I tried to avoid overlapping ranges/lines whenever possible
so that I would have a better sense of what the instrument was doing. Manual
and technical papers can help. I found that asking the instrument rep can
also be useful once you can help them towards the answers you are looking
for. A person with experience (rep, colleague, ???) is often the best
starting point to dig deeper.
Take care,
Luciano
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Mick zhou
Sent: Wednesday, August 10, 2011 8:17 AM
To: l.boglione@xxxxxxxx
Cc: Jim Nadolny; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: 2 questions about TRL cal
Luciano,
How about other lines?
Thanks.
Mick
On Mon, Aug 8, 2011 at 10:52 AM, Luciano Boglione
<l.boglione@xxxxxxxx>wrote:
> 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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