The larger diameter of the SMA connectors in relation to the pitch of the traces
necessitates a transition area on the Golden Standard PCB. This region can be
observed as a “Y” or neck down region where the space between the two traces
gradually tapers from the pitch of the two mounted SMA connectors to the pitch of the
two ideal Golden Standard traces.
At lower frequencies (less than 2 GHz in most cases), most effects of the SMA and
transition area can be ignored. However, the electrical length of these sections can
have an effect on some parameters, so their length should be carefully considered in
correlating measured results to simulations. The SMA connectors and the “Y”
segments add about 1.525 inches to the total path length, which brings the total
assembly path length to approximately 6.675 inches. Experimenting with the effects of
the transition area as compared to the ideal structure through simulation can lead to
valuable insight.
At higher frequencies, the effects of the transition area become easily observable and
can begin to dominate measurements. For evaluating certain test and simulation
methods such as de-embedding, the effects of the SMA connectors can be used to
great benefit. These features can be simulated using full wave 3D solvers, and with
many 2D and 2.5 D modelers as well. Be sure to check out Samtec’s web site as more
in depth discussions on characterizing and de-embedding these effects will soon be
available.
The physical boards also deviate from the ideal structure in the connection of the upper
and lower ground planes. As mentioned earlier, in the ideal case, the two ground
planes are at equal potential. This is not easily achievable in a simple, real world
construction. The physical Golden Standard boards are constructed with multiple vias
connecting the top and bottom ground planes. The vias are of course, non ideal, but at
lower frequencies they function quite well.
The vias also add features which can be studied to gain insight into model accuracy.
For example, in some modeling software, the board can be analyzed by setting all
ground planes at equal potential. A second simulation can be made where the upper
and lower planes are treated as separate conductors tied together periodically by vias
or posts. Of course, a 3D solver can be used to model the structure as exactly as
constructed. By simulating the Golden Standard using several techniques of varying
accuracy (and related varying run times), valuable insight can be gained into which
modeling approaches are best suited for various situations.
The physical Golden Standard boards are ideal for evaluating new test procedures.
Many recent developments in test technology are based on post processing initial test
data. The preliminary data can be converted between time and frequency domains
using Fourier transform techniques. For example, data obtained from TDR
measurements can be converted to frequency domain, thus replicating a network
analyzer measurement. Similarly, frequency domain data obtained from a network
analyzer can be converted into the time domain so that TDR data can be simulated.
Model extraction software is also available which allows time or frequency domain data
obtained from measurement of a physical sample to be converted into a model suitable
for use in computer simulation. A similar process is used in de-embedding techniques,
where the effects of test fixtures or transition structures can be quantified and removed
from test measurements so that the effects of the device under test can be isolated and
observed.
Unfortunately, each of the processes mentioned above is also a source of test
uncertainty. A well characterized device such as the Golden Standard can be
invaluable in isolating and quantifying any errors present in the test environment. Some
representative test data is provided below.
Summary
The Samtec Golden Standard is a practical tool for learning to properly use electrical
modeling and simulation software. The ideal standard allows validation of models and
simulations by comparison of accurate analytical solutions with simulated data.
The Samtec Golden Standard physical boards are more complex than the virtual
standard because of the test instrumentation interconnect structures and because of
variation in physical dimensions and material properties. But, they provide a quick and
simple method for comparing real world measurements with simulations. They also
provide an excellent vehicle for studying more complex test procedures such as deembedding
and for validating 3D simulations.
Samtec has performed many simulations of the Golden Standard board using various
commercially available software packages, and we also have tested physical boards
using multiple procedures and instruments.
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