[SI-LIST] Re: 2 questions about TRL cal
- From: Mick zhou <mick.zhou@xxxxxxxxx>
- To: bob_schaefer@xxxxxxxxxxx
- Date: Thu, 11 Aug 2011 08:34:25 -0400
Bob,
So, overlap is not mandatory.
How about the delays of lines ? If required, absolute delays of relative to
the Thru?
Thanks,
Mick
On Wed, Aug 10, 2011 at 2:08 PM, <bob_schaefer@xxxxxxxxxxx> wrote:
> The overlap doesn't improve the phase accuracy of the TRL calibration.
> Specifying a slight overlap in the calkit definition ensures real number
> comparisons on previous generations of hardware won't fail and you have a
> missing point. As far as the algorithm on how the lines are used for
> Agilent PNA network analyzers, see below:
>
> 1. The calkit standards are used in the order they appear in the calkit
> definition
> 2. If the standard is specified for a specific cal class it is used over
> the entre frequency range specified for that standard if needed.
> 3. If that standard doesn't cover the complete frequency range the search
> continues until another standard for that class is found and it is used.
>
> For example using the calkit definition below:
>
> Standard Start Freq Stop Freq
> Line1 500 MHz 3 GHz
> Line2 2.5 GHz 15 GHz
> Load 0 MHz 1 GHz
>
> If the frequency range for calibration is 10 MHz to 15 GHz and the step
> size is 10 MHz, Line1 is used from 500 MHz to 3 GHz. Then Line2 is used from
> 3.010 GHz to 15 GHz. Finally, the load is used from 10 MHz to 490 MHz. Note
> changing the order will change the frequency ranges used for each standard.
> For example if the load is specified first - it will be used for 10 MHz to 1
> GHz, then line 1 will be used from 1.010 GHz to 3 GHz. Hopefully this helps.
>
> Back to the phase accuracy question. First of all it is not just phase
> accuracy, but accuracy in general. Instead of just overlapping the ranges,
> it is better to specify the range more narrowly. Generally the industry
> recommends that you use standards no more than 8:1 range. Although there are
> people who use 10:1. Metrology grade calkits typically try to use the
> standards over a 3:1 range. Economically, 5:1 is most typical. Instead of
> using a standard (8:1) from 20 degrees to 160 degrees (relative to the
> thru), it is better to use the standard (5:1) from 30 degrees to 150 degrees
> for example. Or if there is overlap in your standards, carefully specify the
> start and stop frequencies to narrow the range the standard is used over.
>
> Regards,
> Bob Schaefer
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Luciano Boglione
> Sent: Wednesday, August 10, 2011 9:23 AM
> To: 'Mick zhou'
> Cc: 'Jim Nadolny'; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: 2 questions about TRL cal
>
> 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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