Text preview for : a-132.pdf part of HP a-132 HP Publikacje a-132.pdf
Back to : a-132.pdf | Home
DE-EMBEDDED MEASUREMENTS
USING THE HP 8510
MICROWAVE NETWORK ANALYZER
Glenn Elmore
Network Measurements Division
1400 Fountaingrove Parkway
Santa Rosa, CA 95401
RF &. Microwave
Measurement
Symposium
and
Exhibition
rliO'l HEWLETT
a:~ PACKARD
www.HPARCHIVE.com
DE-EMBEDDED MEASUREMENTS USING
THE HP8510 MICROWAVE NETWORK ANALYZER
This paper describes a technique for modifying the error coefficients used inside
the HP 851 OA to provide a measurement vantage point different from that which
normal calibration and measurement techniques will allow. Such modification enables
the HP 851 OA to display data as though it had been calibrated at a measurement plane
separated from the actual calibration plane by an embedding network. This technique,
called de-embedding, enables direct device measurement at measurement planes for
which suitable calibration standards are unavailable or inconvenient to use.
While not totally general, the technique can accommodate many fixturing
applications (the same ones to which conventional calibration techniques apply),
particularly if certain attributes are included in the design and fabrication of the
fixture.
The technique may be easily extended to allow embedding the device under test in a
hypothetical network to allow viewing the device as though it were actually in a
circuit with such a network.
Some examples are given which demonstrate the measurement of a packaged
transistor in a fixture with various amounts of de-embedding. Finally, the same
transistor is shown de-embedded from the entire fixture and with a matching/filter
network embedded allowing real time observation of the "finished amplifier"
performance as a function of bias conditions.
Author: Glenn Elmore, R& D Engineer, HP Network Measurements Division, Santa
Rosa, CA. The author has been with HP since 1972. The majority of that time was
spent as a member of a lab team developing swept microwave sources, including the
HP 8350 family of broadband plug-ins. Since 1981, he has been involved with the
development of the HP 8511-8515 test sets for the HP 8510 and most recently was
responsible for the development of the hardware and algorithms used as part of the
HP 85014A Active Device Measurements Pac.
2
www.HPARCHIVE.com
INTRODUCTION
At microwave frequencies it becomes difficult to directly measure components and devices.
Although automatic network analyzers such as the HP 8510 can make direct measurements when
calibration standards with the same connector type as the device under test are available, many times
the device cannot be connected directly to the calibration plane.
This paper describes a way to use the HP 8510 to make measurements exactly as though it had
been calibrated at the plane of the device or component which is to be measured. This allows the
HP 8510 to directly display the device characteristics by using its built-in error correction ability to
remove known fixture influences from the measured data.
In addition, an extension of this technique is presented which allows the measurement of a real
device as though it were part of a hypothetical network. This new technique, called embedding,
offers a powerful blend of circuit analysis and realtime measurement.
WHAT IS DE-EMBEDDING?
Errors are a fact of life in virtually every measurement system. fn the real world, any
information obtained about the characteristics of a subject or device relative to some measurement
standard is likely to be in error. Generally, the information available at the "output" of a measuring
instrument or organ deviates from, or is a corrupted version of, the desired information.
In general, a measurement process consists of some kind of stimulus or perturbation of the
object of interest (located at the Device or Measurement Plane) followed by an examination of the
results (obtained at the Data Collection Plane).
The data which is collected may be in error due to many causes; the stimulus may not be the
same as that which is desired or expected, the object (hereafter called the Device Under Test or
OUT) may not be situated in the desired environment, other characteristics of the measuring
environment may "corrupt" the collected data, and the measuring instrument at the Data Collection
Plane may itself be in error or affect the measurement.
3
www.HPARCHIVE.com
Fortunately, it is often possible to achieve results
nearer to those which are desired through analysis and
ERROR CORRECTION
correction of the "raw" data taken at the Data
Collection Plane. To the degree to which the causes of
error can be understood and their affects on the
"actual" or desired data taken into account and
corrected, the desired data may be obtainable. As the
cartoon illustrates, error correction of this sort is a
common occurrence.
3953
Automatic network analyzers (ANAs) perform this
measurement and error correction process in the
domain of network measurements. When measuring a NETWORK ANALYZER
one-port OUT, the ANA acquires data at a plane ONE-PORT ERROR CORRECTION
which is separated from the OUT by a corrupting
Network Error
network. The model of this network is given the name Analyzer "Adapter"
Error Adapter.
q(!I ., ,
.....
...
~
......
~ ~
I
I
I
I 9 OUT
Data Measurement
Collection Plane
Plane
3954
In order for the ANA to correct the raw data and
provide the desired data, it is necessary to have a HP 8510 ERROR CORRECTION (ONE-PORT)
description of the Error Adapter. This must be a Characterization