Poulin

The transmission line characteristics of the balanced interconnect networks used in high speed digital systems have a major impact on the digital signal quality or integrity of the digital signals. The traditional instruments used for characterizing transmission lines are Vector Network Analyzers (VNA) and Time Domain Reflectometers (TDR). Since most commercial test equipment has single ended test ports, some means of converting from single ended to differential transmission lines must be utilized. This is accomplished on a VNA through either the use of a balun transformer or the use of a multiport testset on the VNA. The advantages and limitations of both approaches will be analyzed. Historically, most of the aspects of digital systems were analyzed using time domain instruments such as oscilloscopes and logic analyzers. The Time Domain Reflectometer (TDR) is the natural extension of these time domain measurements applied to transmission lines. TDR’s can be used to measure impedance of a transmission line as well as the location of any discontinuities along a transmission line. When the TDR is used as a Time Domain Transmission (TDT) it can be used to measure attenuation and delay of a transmission line. A Vector Network Analyzer (VNA) is inherently a frequency domain instrument. However, through the use of Inverse Fourier Transforms (IFT), the VNA can make TDR and TDT. The advantages and limitations of both approaches will be analyzed. In the case of a multiport VNA used to make balanced measurements, there are two approaches commonly use. One approach is to rely on the inherent linear nature of a balanced transmission line and to mathematically derived the balanced transmission line characteristics through superposition while stimulating just one side of the balanced transmission line at a time. The other approach is to use an actual differential stimulus, hence the name “true differential”. The advantages and limitations of both approaches will be analyzed. Finally, unlike single ended transmission lines, balanced transmission lines rarely have “standard” connectors. This makes it necessary to create custom fixtures to transition from single ended “standard” connectors to the balanced transmission line under test while maintaining good signal integrity. Several fixture approaches will be discussed.

Biography: Dennis D. Poulin (S’76-M’77) received the B.S.E.E. and M.S.E.E. degrees from the Massachusetts Institute of Technology (MIT) in 1977. He initially joined Hewlett Packard, Microwave Technology Center, Santa Rosa, CA in June of 1977 and has been heavily involved in RF and Microwave characterization and measurement techniques throughout his career. He has done extensive work on large signal device characterization and nonlinear modeling. He is the original creator of the large signal measurement techniques of “Real Time Load Pull”(1979), “Harmonic Load Pull(1979)”, “High Gamma Active Tuners(1979)” and “Non-interactive Harmonic Tuners(1979)”. He has published several papers on load pull measurements as well as other large signal characterization techniques.
He is a member of the adjunct faculty for Northeastern University teaching various classes in the B.S.E.T. program.
He is currently working for Anritsu Company as a Senior RF and MW Field Applications Engineer based in New England specializing in Vector Network Analysis, Spectrum Analysis and Vector Signal Analysis. He has been heavily involved in Vector Network Analysis and TDR applications of balanced devices and transmission lines including the use of baluns and multiport VNA’s to obtain balanced and mixed mode S Parameters.

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