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Ed Lee
Ed Lee
Ed Lee has been around EDA since before it was called EDA. He cut his teeth doing Public Relations with Valid, Cadence, Mentor, ECAD, VLSI, AMI and a host of others. And he has introduced more than three dozen EDA startups, ranging from the first commercial IP company to the latest statistical … More »

Thru-reflect line vs. in-situ de-embedding

January 11th, 2016 by Ed Lee
Chris Scholz

Chris Scholz

Today we wrap up our interview with Chris Scholz, Product Manager, Vector Network Analyzers, R&S North America, discussing the different approaches to Signal Integrity.

Ed:  It’d be great if you could give us a brief comparison on approaches you’ve dealt with.

Chris:  Sure! Signal Integrity applications use baseband data with bandwidth up to 10s of GHz impedance, matching of DUTs in Signal Integrity applications is relatively poor. Looking at TRL-based calibration techniques that have been automated by some vendors, these techniques generally fail to provide accurate results beyond a few GHz.

Ed:  What’s TRL?

Chris:  Thru-reflect line.

For our customers, in-situ de-embedding (ISD) has shown to be the most accurate de-embedding technique available to date. One of the nice side effects of ISD is that it results in causal measurements what are beneficial for further processing standard design tools.

Because the Signal Integrity engineers deal with baseband signals, they face a set of unique challenges that are marginally important for RF engineers. For wireless systems, transmission channels are narrow band and separated from each other.

By contrast, Signal Integrity deals with baseband signals. This means that signals experience impairments that span from close to DC to the maximum frequency that the channel supports. This also means that digital signals are prone to picking up low frequency impairments such as power supply noise, they are prone to frequency dependent loss at high frequencies and they pick up broadband impairments such as various types of crosstalk.

Transmission lines that are not well balanced have the tendency to pick up electromagnetic interference and can radiate electromagnetic energy and thus interfere with other transmission lines.

Ed:  How do you get that balance, minimize the interference?

Chris:  To characterize these kind of effects, it has become customary to use multi-port Vector Network Analyzers. Network Analyzers with more than four ports are still relatively uncommon though, and the test and measurement industry is beginning to offer multi-port VNAs at the required price points. Rohde & Schwarz has been pioneering this industry.

Depending on the required performance and price points customers can choose between multi-port Network Analyzers that use switch matrices or true-multiport VNAs.

Ed:  Sum up for us — what do engineers need to do with Signal Integrity today? 

Chris:  In many ways VNAs are becoming the “Swiss Army Knife” of Signal Integrity measurements. If it is for accurate channel characterization, reliable de-embedding, fault analysis or material testing, VNAs are no longer the specialist tools they used to be a decade ago. Going forward, for Signal Integrity engineers it will become

more and more important to be proficient in frequency domain techniques and measurements.

Ed:  Quite a bit to digest here, Chris.  Thanks for talking with us today.


Look for Rohde & Schwarz at DesignCon, booth #643.  

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