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"Jan Verspecht b.v.b.a." is a high-tech company located near Brussels, Belgium. The company was established in January 2003 by Jan Verspecht, who has more than 19 years of experience in the RF and microwave instrumentation industry. The company specializes in consulting and intellectual property development related to the measurement and modeling of nonlinear microwave components and systems. Example applications and topics are: X-parameters, poly-harmonic distortion (PHD) model, nonlinear distortion, fundamental and harmonic loadpull, "Hot-S22", "Large-Signal Network Analysis", spectral regrowth, black-box frequency domain modeling, harmonic phase calibration, current and voltage waveform measurements, high-speed digital signal integrity, broadband oscilloscope calibration, ...

## Founder biography |

Jan Verspecht graduated from the "Vrije Universiteit Brussel" (VUB) in 1990 and he joined the Hewlett-Packard Co (HP) the same year. He started working as a research engineer for the "Network Measurement and Description Group", at that time part of HP's Network Measurement Division. During the first 5 years Jan was sponsored by the "HP Fellowship Program" which allowed him to combine his job with working towards a Ph.D. degree. He received the doctoral degree from the "Vrije Universiteit Brussel" in November 1995. As a Ph.D. student Jan developed calibration procedures for a measurement system to characterize nonlinear microwave devices. The most significant contributions of this period were the advancement of the "nose-to-nose" calibration procedure for broadband sampling oscilloscopes and its use as a harmonic phase standard for voltage/current waveform measurements. During the same period, Jan contributed to the RF hardware and system level software of the first 4-channel prove-of-concept prototype of the "nonlinear network measurement system" (NNMS).

From September 1991 until October 1992 Jan interrupted his job at HP in order to fulfill his compulsory military service. As an officer of the reserves he worked for the microwave lab of the Belgian army. His main responsibility was the development and characterization of anti-radar stealth technology.

After receiving his Ph.D. degree Jan continued to work on maturing the prototype NNMS system. At the same time he started investigating how the NNMS system could be used for extracting measurement based black-box frequency domain models for systems and components. Being confronted with the limitations of the Volterra theory to describe so-called "hard nonlinear" behavior he invented a multi-frequency "Describing Function" concept. Unlike the Volterra theory, which can be considered as a special case of the "Describing Function", the new mathematical framework allows to describe very hard nonlinear behavior as encountered in e.g. comparators, harmonic mixers, samplers and other hard clipping devices.

Confronted with the need for smart experiment design in order to extract "Describing Function" models, Jan started experimenting with the combination of loadpull technology and the NNMS. The result was a cooperation with researchers from the French IRCOM institute where it was shown how efficient power amplifiers could be designed by "waveform engineering". This technique implies the tuning of fundamental and harmonic impedances while monitoring the voltage and current waveforms at the terminals of a power transistor.

In 1995 Jan added modulated measurement capability to the NNMS. This made it possible to perform unique voltage/current waveform measurements under modulated large-signal operating conditions.

In 1999 Jan started working for Agilent Technologies, the HP spin-out company. Jan was promoted to the position of "Technical Lead" for the "Measurement Center of Technology", an internal consulting organisation. While working on further developing the NNMS (by that time called "Large-Signal Network Analyzer" or LSNA), he also assisted early customers with using the NNMS system for their specific applications. This work resulted in 5 patent applications.

Early 2003 Jan founded the company "Jan Verspecht b.v.b.a." and started working as an independent consultant.

Working as an independent consultant for Agilent Technologies Jan has since that time developed the X-parameters, which are based on the "poly-harmonic distortion" (PHD) model. This is a black-box frequency domain model that can be derived from simulations as well as from measurements. The X-parameters are fully compatible with the Agilent Advanced Design System (ADS) simulator.

Together with the XLIM institute in France (formerly IRCOM) Jan has developed advanced time domain loadpull techniques for characterizing microwave power transistors.

In 2007 Dr. Jan Verspecht was elevated by the IEEE Board of Directors to the grade of IEEE Fellow.

In 2008 Jan co-founded the company Verspecht-Teyssier-DeGroote SAS (www.vtd-rf.com). This company, in short named VTD, is a spin-off from the XLIM research institute and is based in Brives-la-Gaillarde, France. VTD builds and sells the SWAP-X402 and wave probes. The SWAP-X402 is a broadband receiver that, in combination with wave probes, provides an affordable way to add time domain loadpull capability to virtually every loadpull setup.

In 2009 Jan won the IMS 2009 Best Oral Paper Presentation Award for Wednessday, June 10th, 2009 with the paper "Extension of X-parameters to Include Long-Term Dynamic Memory Effects".

*Large-Signal Network Analyzer Technology*

- Invention of loadpull measurements based on the use of a low insertion loss wave probe
- Development of the RF hardware (test-set and frequency convertor)
- Development of the system level software (Mathematica and Scilab code)
- Invention of the traceable harmonic phase calibration procedure
- Invention of accurate IF phase calibration procedures
- Invention of the "dynamic bias" measurement concept which allows to add the measurement of time varying bias signals (typical under modulated signal conditions) to the LSNA data
- Invention of the sampling frequency convertor algorithms, allowing e.g. optimal use of the IF bandwidth with modulated signals
- Development of the relative on-wafer and coaxial calibration procedures, including LOS, LRRM and Multiline-TRL
- Development of the absolute on-wafer and coaxial calibration procedures to measure power and harmonic phase

*Automatic RF Techniques Group (ARFTG) *

- Recipient of the "ARFTG 2002 Technology Award" for the development of large-signal measurement technology
- Author of the "ARFTG Large-Signal Network Analysis Short Course"

- Advanced theoretical and practical study of the "nose-to-nose" calibration procedure
- Recognition of timebase errors as a significant source of distortion in the frequency domain
- Development of methods to accurately characterize timebase errors and to compensate for the resulting frequency domain errors

- Development of the Poly-Harmonic Distortion (PHD) model
- Invention of the multi-frequency "Describing Functions", a powerful mathematical framework for black-box frequency domain modeling
- Invention of the scientifically sound "Hot S22" which takes into account the phase relationship between the small signal b2 and the large signal a1 wave
- Invention of measurement based "nonlinear scattering functions" which are an extension of the classical S-parameters towards the presence of harmonics and large signal components. "Nonlinear scattering functions" can accurately predict component behavior under fundamental and harmonic loadpull conditions
- Development of black-box frequency domain models derived from measurements under modulated large-signal excitation
- Invention of measurement capability for large-signal input match, harmonic distortion, compression characteristics and AM-PM conversion under modulated excitation
- Invention of the X-parameters
- Invention of a way to extend X-parameters to include long-term dynamic memory effects

© 2004 - Jan Verspecht bvba