Very good points about when a VNA is required for specific measurements.
I agree there are many measurements where you need the accuracy and
Vector measurement capabilities of a Network Analyzer.
My measurement accuracy comment was specific to the Power Delivery
Subsystem measurement Mikhail mentioned in Lee Ritchey's & John Zasio's
"Right The First Time" book. (I thought Mikhail was referring to the
capacitor and Power Deliver Subsystem measurements described in Volume
I, Chapters 34 & 37). In that book a Spectrum Analyzer was being used
to characterize capacitors and board plane capacitance to determine what
types of capacitors and how many should be used to build a sufficient
power delivery subsystem. Later in the book a Spectrum Analyzer was
used to verify the power delivery subsystem on a finished board with
capacitors installed to check everything had been done correctly
(including that there was sufficient high frequency power plane
capacitance).
For the measurement Mikhail was referring to you're trying to
approximate the high frequency impedance of capacitors and figure out
how many of each size you need to use. Whatever values you measure
here, the actual capacitor impedance could vary somewhat for the
manufactured parts you will get later during production, so you have to
add additional capacitance margin to cover this for the final design
implementation anyway. So in this case I believe a Spectrum
Analyzer/Tracking Generator combination had good enough accuracy for
this particular type of basic measurement (for those who might not
already own a VNA).
Of course it's always good to use a VNA for these measurements if you
have one. "Network Analysis" is what they're made for and is part of
their name. ;-)
Chuck
Chuck Corley
National Instruments
-----Original Message-----------------------------------------------------------------------
From: Ihsan Erdin
Sent: Tuesday, November 03, 2015 7:36 PM
To: olaney@xxxxxxxxx
Cc: matusov@xxxxxxxxxxxx ; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: PDN impedance measurements
Orin has a point. A tracking generator+DUT+SA combination will yield a
single parameter at a time and it will be in scalar format. If the
output
of TG and input of SA are connected at different test points of the
DUT, SA
will display |S12| parameter between these two points. The output data
from
SA can be used to have an idea about resonances etc. but cannot be used
to
characterize the DUT in a circuit simulator because of the scalar
nature of
data. A VNA, on the other hand, will output both the real and imaginary
part (or magnitude and phase) of data in complex form (and at all
probed
port parameters, S11, S12, etc.), hence the name for VECTOR network
analyzer. A VNA output can directly be fed into a circuit simulator
which
can massage it for passivity, etc.
Regards.
Ihsan Erdin
On Tue, Nov 3, 2015 at 5:05 PM, Orin Laney <olaney@xxxxxxxxx> wrote:
Spectrum analyzer + tracking generator is essentially an S21-only
scalar
network analyzer. The VNA is a more complete and versatile instrument.
Orin
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
On
Behalf Of Mikhail Matusov
Sent: Tuesday, November 03, 2015 1:31 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] PDN impedance measurements
Hi gurus,
Please forgive my ignorance, but could someone enlighten me on what
are
the
limitations of the PDN impedance measurement method using a spectrum
analyzer and tracking generator as described by Lee Ritchey in his
"Right
The First Time" book compared to using a VNA as described for example
in
Istvan Novak's "Frequency-Domain Power-Distribution Measurements - An
Overview" paper? I don't have practical experience with network
analyzers
but very familiar with the spectrum analyzers hence the question.
Thanks,
/Mikhail
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