Microwave The ory and Techniques Society

\nProfessor Patrick Roblin\, The Ohio St ate University

\n\nThe advent of nonlinear vect or network analyzers (NVNA) has stimulated the introduction of new paradig ms in microwave engineering for (1) the measurement\, (2) the modeling and (3) the design of nonlinear microwave circuits such as microwave power am plifiers and oscillators.

\nThis talk will start with a review of ve ctor large-signal microwave measurements for the acquisition of the phases and amplitudes of the multi-harmonic incident and reflected waves at the ports of a nonlinear device. The various types of NVNA architecture avail able\, the procedure used to calibrate them and the calibration traceabili ty will be presented.

\nNext the behavioral models used for the r epresentation of the measured multi-tone multi-harmonic data will be revie wed. This will include the general multi-harmonic Volterra functions for CW periodic nonlinear RF excitations\, the X-parameter/S-function approxim ations for mildly nonlinear RF excitations and their extension for modulat ed multi-harmonic signals.

\nCircuit-based nonlinear microwave model s can also be directly extracted from large-signal measurements for a targ eted range of operation. Examples of SOS-MOSFET and GaN models extracted and verified using a few real-time active load pull (RTALP) measurements w ill be presented. The efficient phase sweeping of the RTALP drastically r educes the number of large-signal measurements needed for the model develo pment and verification while maintaining the same intrinsic voltage covera ge as in conventional passive or active load–pull systems. The bias depend ence of the charges and device IV characteristics can then be simultaneous ly extracted from these large-signal RF measurements using artificial neur al networks (ANN).

\nNVNA’s also find application in the design of power amplifiers (PA). To optimize the power efficiency of PAs\, specif ic internal modes of operation are usually targeted at the device current source reference planes as estimated using nonlinear deembedding. However given the tremendous large search space for the multi-harmonic terminatio ns for waveform engineering\, it is beneficial to first use a nonlinear em bedding device model to predict from the desired internal mode of operatio n\, the required amplitude and phase of the multi-harmonic incident waves at the transistor measurement reference planes. The verification of the r esulting amplifier power efficiency optimization can then be performed usi ng NVNA measurements. Examples of such design for Doherty and Chireix amp lifiers will be presented.

\nFinally in addition to CW signals\, p ulsed or modulated signals can also be measured by NVNAs. This is particu larly important for nonlinear devices such SOS-MOSFET or GaN HEMTs which a re affected by various low-frequency memory effects such as parasitic bipo lar junction transistor effects\, self-heating\, and cyclostationary charg ing of traps. Recent techniques reported for low-duty rate pulsed and mod ulated RF NVNA measurements will then be reviewed to shine new light in th e time-varying response of transistors excited by high peak to average pow er ratio (PAPR) modulated signals.

\nSocial Refreshments begin at 5: 30PM

\nMeeting and talk from 6:00PM to 7:30PM

\nMIT Lincoln La boratory\, Forbes Road\, Cafeteria (open to the public)

\nDirectio ns: http://www.ll.mit.edu/about/mapForbesRoad.html)

\n X-TAGS;LANGUAGE=en-US:Microwave Theory and Techniques END:VEVENT END:VCALENDAR