J.M. Nebus

Accurate RF and microwave system level modeling of wideband nonlinear circuits

Accurate system level simulation is indispensable for efficient RF communication system design. However system level models of nonlinear circuits are today very limited by their inability to handle nonlinear memory effects. The paper describes a new approach of system-level modeling which accounts efficiently for nonlinear envelope memory effects of wideband amplifiers, multipliers and mixers.

A new behavioral model taking into account nonlinear memory effects and transient behaviors in wideband SSPAs

Accurate and non quasi-static behavioral models of SSPAs taking into account nonlinear memory effects become of prime importance for a breakthrough in system level analysis and design of wideband digital communication systems. This paper describes a new method to characterize and integrate memory effects in nonlinear behavioral models of SSPAs allowing to reproduce both transient and steady state behaviors.

Analysis of low frequency memory and influence on solid state HPA intermodulation characteristics

A theoretical analysis using two-tone simulations and practical measurements of low frequency memory impact on third order intermodulation (IM3) on HBT as well as HFET power amplifiers is carried out. A particular emphasis is placed on the thermal origin for the HBT case and electrical origin for the HFET case of these low frequency nonlinear phenomena.

An improved behavioral modeling technique for high power amplifiers with memory

The introduction of frequency dependence in system level nonlinear behavioral models is of prime importance as wideband signals are going to be massively used with nonlinear SSPA. This paper describes an improved technique to model envelope memory effects for amplifiers exhibiting both high and low frequency memory.

A novel computerized multiharmonic active load-pull system for the optimization of high efficiency operating classes in power transistors

A fully automated multiharmonic load-pull system allowing accurate measurement and control of the first three harmonic load terminations of RF and microwave transistors is presented in this paper. The technical originality of the proposed system lies in that the first, second and third harmonic load terminations can be independently and automatically monitored and fixed while varying the input power driving the transistor at the fundamental frequency. Appropriate hardware and software allow fast and automatic plots of power/efficiency performances of DUTs versus input power for different harmonic loadings. To demonstrate an attractive application of the system, measurements of a 1800 /spl mu/m gate periphery MESFET at 1.8 GHz for mobile communication applications are presented. Both suitable harmonic load terminations and nonappropriate ones yielding respectively optimum and poor power added efficiency are given.<<ETX>>

Time-Domain Calibrated Measurements of Wideband Multisines Using a Large-Signal Network Analyzer

This paper presents a calibrated measurement technique that enables phase and magnitude measurements of wideband multisines. This study is based on the use of a large-signal network analyzer (LSNA) performing harmonic sub-sampling and a fine frequency grid (20 MHz) comb generator calibrated using a high-frequency 50-GHz equivalent-time sampling scope. This comb generator is used as a harmonic phase reference generator for the calibration of the LSNA. The research reported here is applied to L-band multisine measurements, but it can be extended to higher microwave frequencies. The motivation of this study is to measure the multipactor phenomena effect in output RF multiplexers of satellite payloads.

Two-Stage GaN HEMT Amplifier With Gate–Source Voltage Shaping for Efficiency Versus Bandwidth Enhancements

In this paper a two-stage 2-GHz GaN HEMT amplifier with 15-W output power, 28-dB power gain, and 70% power-added efficiency (PAE) is presented. The power stage is designed to operate under class F conditions. The driver stage operates under class F-1 conditions and feeds the power stage with both fundamental and second harmonic components. The inter stage matching is designed to target a quasi-half sine voltage shape at the intrinsic gate port of the power stage. The goal is to reduce aperture angle of the power stage and get PAE improvements over a wide frequency bandwidth. In addition to the amplifier design description, this paper reports original time-domain waveform measurements at internal nodes of the designed two-stage power amplifier using calibrated high-impedance probes and large signal network analyzer. Furthermore, waveform measurements recorded at different frequencies show that aperture angle remains reduced over large frequency bandwidth. In this study, a PAE greater than 60% is reached over 20% frequency bandwidth.

Hot small-signal S-parameter measurements of power transistors operating under large-signal conditions in a load-pull environment for the study of nonlinear parametric interactions

This paper presents a setup that enables wide-band (in-band and out-of-band) measurements of hot small-signal S-parameters of nonlinear devices driven by a large-signal single tone (namely, the pump signal). A load-pull characterization is performed at the pump frequency (F/sub 0/), while hot small-signal S-parameters are measured with a perturbating signal at a frequency (f) by the use of a probe tone. Basically, the frequency of the probe tone is swept over a wide bandwidth (at the present time from 300 MHz up to F/sub 0//2). A higher frequency range, from near dc to KF/sub 0/, will be implemented in a similar manner. The measurement setup reported here is applied to on-wafer measurements of S-band HBTs. Hot small-signal S-parameter measurements versus large-signal load impedance and pump level will be shown. An application to the prediction of parametric oscillations will be demonstrated. A parametric oscillation predicted at 373 MHz is confirmed by spectrum measurements.

A design method for high efficiency class F HBT amplifiers

In this paper, we report on the class F operation of HBTs. A temperature dependent model of a 240 /spl mu/m/sup 2/ GaInP-GaAs HBT (THOMSON-CSF) was extracted from pulsed I/V and pulsed S-parameter measurements and validated by load-pull measurements. An extensive large signal HB analysis, based on the substitute generator technique, was achieved to optimize the load impedance at harmonic frequencies required for class F operation. Furthermore, the performances of the transistor in terms of added power, power added efficiency and dissipated power, were investigated under different bias modes (i.e.: constant base voltage, constant base current and self bias modes). We show that the bias mode has a great influence on the HBT linearity.

Large-Signal Time Domain Characterization of Microwave Transistors under RF Pulsed Conditions

This paper describes a time domain measurement technique of large-signal RF pulsed waveforms, based on Agilent Nonlinear Network Measurement System (NNMS). A transistor is biased under pulsed conditions and the RF is applied during bias pulses. The paper shows how the time domain RF measurements are acquired during the pulses. Up to 12 harmonic frequencies are taken into account, in order to provide an accurate time domain voltage and current description at both transistor terminals.