October 2014 • The PCB Design Magazine 23
feature
SINk OR SWIM AT 28 GBPS continues
much faster than the direct convolution. Thus,
we will naturally use rational approximation for
all time-domain computations here.
After all modeling decisions on what to com-
pare and how to compare are made, we run the
post-layout analysis for all 27 structures on the
CMP-28 platform and compare the magnitudes
of S-parameters, phase and group delays (and
optionally phases), TDR computed with Gauss-
ian step with 20 ps 10–90% rise time and eye
diagrams computed with PRBS signal with 25
ps rise and fall time generated with LFSR with
order 32. Two examples of the validation are
shown in Figure 5 and Figure 6.
Results for microstrip line link with two ca-
pacitive vias (Figure 1, structure 1) are shown in
Figure 5. It contains connectors with adapters on
both ends, microstrip launches with through-
hole vias, two segments of microstrip line with
about 50 ohm impedance, two vias and one
segment of wide microstrip line in the middle.
The link is not optimal by design and represents
highly reflective structure. We can conclude that
the correlation is very good in this case and all
discrepancies may be explained by the manufac
-
turing and material properties variations.
Results of validation for a relatively low-re-
flective structure are shown in Figure 6. It is a
simple 8-inch segment of single-ended stripline
with launches, connectors and adapters on both
ends (Figure 1, structure 2). The launches in this
case are back-drilled with the goal to have less
than 10-mil via stubs. Though, the manufac-
turer specified that the stubs may have +- 5 mil
variation. 10-mil stubs were used in the model.
Considering this and other types of variations,
the correlation is acceptable. See all details of
the analysis and analysis-to-measurement cor-
relation for all 27 structures on CMP-28 plat-
form in Reference
[5]
.
Conclusion
A systematic process of the analysis-to-
measurement validation up to 50 GHz is in-
troduced here. The process is illustrated in this
article with the CMP-28/32 validation platform
and Simbeor software. Note that the validation
problems can fall into three categories: manu-
facturing, measurement, and analysis, and only
measurement quality and the interconnect
analysis parts are covered here. Following the
procedure, you can easily qualify or reveal prob-
lems in your signal integrity software of choice.
Just try to do the analysis of all 27 test structures
on CMP-28/32 validation platform and swim at
28 Gbps and beyond.
Do not forget to compare the productivity
and cost of the tools. Finally, is your software
qualified for the analysis of PCB interconnects
running at 50 Gbps? The question is rhetorical
so far.
PCBDESIGN
References
1. Y. Shlepnev, Measuring correlation to 50
GHz and beyond, The PCB Design Magazine,
February 2013, p. 10-21.
2. CMP-28/32 Channel Modeling Platform
with Simbeor EDA Kit, Wild River Technology.
3. Simbeor Electromagnetic Signal Integrity
Software, Simberian Electromagnetic Solutions.
4. Y. Shlepnev, A. Neves, T. Dagostino, S.
McMorrow, Measurement-Assisted Electromag-
netic Extraction of Interconnect Parameters on
Low-Cost FR-4 boards for 6-20 Gb/sec Applica-
tions, DesignCon 2009
5. Guide to CMP-28/32 Simbeor Kit, 2014.
6. Y. Shlepnev, Reflections on S-parameter
Quality, IBIS Summit at DesignCon 2011,
7. Y. Shlepnev, PCB and package design up
to 50 GHz: Identifying dielectric and conductor
roughness models, The PCB Design Magazine,
February 2014, p. 12-28.
8. Y. Shlepnev, System and method for iden-
tification of complex permittivity of transmis-
sion line dielectric, US Patent #8577632, Nov.
5, 2013, Provisional App. #61/296237 filed on
Jan. 19, 2010.
9. Y. Shlepnev, System and method for iden-
tification of conductor surface roughness mod-
el for transmission lines, Patent Pending, App.
#14/045,392 filed on Oct. 3, 2013.
Yuriy Shlepnev, Ph.D., is found-
er and president of Simberian
Inc. He previously served as
principal engineer at Men-
tor Graphics and director of
the Electromagnetic Group at
Eagleware Corporation.
