Denis Barataud

40-GHz/150-ns versatile pulsed measurement system for microwave transistor isothermal characterization

A versatile pulsed I(V) and 40-GHz RF measurement system is described with all the know-how and methods to perform efficient, safe, and reliable nonlinear transistor measurements. Capability of discrimination between thermal and trapping effects with a pulse setup is demonstrated. Capture and emission constant times of trapping effects are measured. A method to electrically measure the thermal resistance and capacitance of transistors with a pulse setup is proposed.

Measurements of time-domain voltage/current waveforms at RF and microwave frequencies based on the use of a vector network analyzer for the characterization of nonlinear devices-application to high-efficiency power amplifiers and frequency-multipliers optimization

A new time-domain waveform measurement system based on the combination of an harmonic source and load-pull setup with a modified vector network analyzer (VNA) is presented. It allows the visualization, the measurement, and the optimization of high-frequency currents and voltages at both ports of nonlinear microwave devices. Measurements of GaAs field effect transistor (FETs) and GaInP/GaAs heterojunction bipolar transistor (HBTs) at L-band were performed to demonstrate the great capabilities of the system. On one hand, voltage and current waveforms at both ports of transistors, working as power amplifiers, were optimized for maximum power-added efficiency. On the other hand, time-domain waveforms of transistors operating as frequency multipliers were optimized for maximum conversion gain. Such results prove the capabilities offered by this new nonlinear time-domain measurement system to aid in designing optimized power amplifiers or frequency multipliers. They also provide valuable information for nonlinear transistor model validation.

An active pulsed rf and pulsed dc load-pull system for the characterization of power transistors used in coherent radar and communication systems

This paper presents a new automated and vector corrected active load-pull system allowing the characterization of microwave power transistors under coherent pulsed RF and pulsed DC operating conditions. Measurements of an S band-Class C-8 Watt silicon bipolar amplifier are shown and demonstrate the ability of our system to accurately characterize power variations and carrier phase shift within the pulse. Source and load-pull measurements of an 8/spl times/30 /spl mu/m/sup 2/ GaInP/GaAs HBT (Thomson LCR) are also reported for different pulse widths.

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.

An improved coupling method for time domain load-pull measurements

This paper describes an efficient coupling method improving the nonlinear time domain large signal load-pull measurements of active devices. This approach consists in a small RF loop fixed near the blended line that takes place between the DUT and the tuner. We take benefit of two advantages: extremely low losses induced by the coupler, and measurements taken very close to the DUT plane. It is shown that this simple coupling solution offers an average directivity better than 15 dB (before calibration) along a wide RF band from 2 to 18 GHz. This solution is compared with the classical approach of a distributed coupler connected before and after the tuner. A LSNA calibration has been performed, it exhibits an average directivity better than 35 dB.

Optimum design of very high-efficiency microwave power amplifiers based on time-domain harmonic load-pull measurements

Due to the large expansion of wireless communications, the need for high-efficiency power amplifiers has emerged. In mobile communication systems, power amplifiers are the most critical elements for the power-dissipation budget. Thus, the operating conditions of active devices have to be optimized using accurate and complementary computer-aided design (CAD) and experimental tools. This paper reports two design methods of high-efficiency power amplifiers. The first one is CAD oriented and based on the substitute generator technique using the nonlinear model of transistors. The second one is based on a specific measurement system of time-domain waveforms using a modified vector network analyzer, coupled with harmonic active load-pull techniques (three active loops). This new setup enables the measurement and optimization of time-domain waveforms at both ports of transistors driven by constant-wave test signals. These two design methodologies are applied to the optimization of an S-band 1-W class-F GaInP/GaAs heterojunction-bipolar-transistor power amplifier.

Characterization and modeling of nonlinear trapping effects in power SiC MESFETs

Trapping effects in power SiC MESFETs are investigated using a pulsed I-V pulsed S-parameters measurement system. It is shown that the main effect comes from substrate (buffer) traps sensitive to the drain-source voltage. Moreover a nonlinear model of the trapping phenomenon, taking into account the electron capture and emission with different time constants allows one to predict experimentally observed I-V and RF power performances of the devices.

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.

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.

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.