In this paper, a Doherty power amplifier for K-band point-to-point microwave radio, developed in TriQuint GaAs 0.15-μm PWR pHEMT monolithic technology, is presented. Highly efficient driver stages on both the main and auxiliary branches have been designed and optimized to boost gain with minimal impact on power-added efficiency. The selected architecture enables a modular combination to reach higher power levels. Matching network structures have been designed, according to simple equivalent circuit approaches, to obtain the desired 10% fractional bandwidth. The fabricated power amplifier (PA) exhibits, at 24 GHz in continuous-wave conditions, an output power of 30.9 dBm, with a power-added efficiency of 38% at saturation and 20% at 6 dB of output power back-off, together with a gain of 12.5 dB. System-level characterization at 24 GHz, in very demanding conditions, with a 28-MHz channel 7.5-dB peak-to-average ratio modulated signal, showed full compliance with the standard emission mask, adopting a simple predistorter, with average output power of 23.5 dBm, and average efficiency above 14%. The measured performance favorably compare with other academic and commercial K-band PAs for similar applications.

This paper presents an accurate and flexible approach to the self-consistent electrothermal modeling of III-N-based HEMTs, combining a temperature-dependent electrical compact model with a novel behavioral nonlinear dynamic thermal model, suitable for circuit-level simulations. The behavioral thermal model is extracted, according to a Wiener-like approach, from a full-scale, finite-element-method-based time-domain 3-D solution of the heat equation. The electrothermal model, validated against dc, pulsed dc, -parameter and large-signal nonlinear measurements, is exploited to assess the impact of thermal memory effects on the device RF performances. In particular, the model allows for a detailed analysis and interpretation of the thermal memory effects on intermodulation distortion. Finally, the proposed approach enables to analyze such features for different thermal mountings, thus providing useful indications for technology assessment.

We present here and in the companion paper (Part II) a general framework for the modeling of semiconductor device variability through the physics-based analysis of the small-change sensitivity. We consider a very general class of dynamic device operation, i.e., the periodic or quasi-periodic large signal (LS) time-varying regime, and we evaluate the sensitivity of both dc and harmonic components of the device dynamic working point with respect to process or physical device parameters. The proposed technique is based on the linearization of the physics-based device model around a nominal parameter, and extends to the dynamic case the already established Green's function approach to the numerically efficient dc sensitivity analysis. As an example of application, we consider a class A GaAs MESFET microwave power amplifier; the sensitivity of the LS working point with respect to doping and gate work function variations is evaluated through the proposed approach and compared with the result of repeated LS amplifier analyses, showing that the numerically efficient small-change sensitivity approach provides reliable predictions for parameter variations up to 10% of the nominal value.

In this work, we present the characterization results for several HEMT GaN-based devices developed by SELEX Sistemi Integrati. Due to the wide band-gap properties of this material, these devices are very well-suited for high-power applications, and must be characterized under strongly nonlinear and high-power conditions. An extensive power characterization of devices fabricated on GaN grown either on SiC or sapphire substrates is carried out, including pulsed I-V, power sweeps, and load-pull measurements in different bias conditions from class A to class B. An active load-pull bench optimized for high-voltage and high-power measurements allows the load-pull characterization to be extended to the whole Smith chart and the optimum loads to be localized, even for devices with almost reactive optimum terminations. The characterization procedure is performed on HEMT devices fabricated with different technologies and different layouts, in order to improve and refine the fabrication methodology and verify the scaling rules and the effects of defects and thermal degradation. SELEX SI devices show a growing maturity, with performances comparable to state-of-the-art technology. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.

We present here and in Part I a general framework for the modeling of semiconductor device variability through the physics-based analysis of the small-change sensitivity. While Part I focuses on the sensitivity of the device terminal currents in periodic large-signal (LS) operation, we extend here the analysis to the linearized device representations, i.e., to the sensitivity of the small-signal (SS) admittance matrix (SS sensitivity) and the conversion admittance matrix (SS-LS sensitivity). The proposed technique is based on the linearization of a physical device model around a nominal process parameter, and on the evaluation of relevant Green's functions linking the parameter variations to the terminal performance. This provides, for the first time, a unified and computationally efficient simulation framework for the device physics-based sensitivity in dc, SS, LS, and SS-LS conditions. To highlight the accuracy of the approach when compared with the incremental evaluation, we discuss two case studies, concerning the SS-LS sensitivity of a class A GaAs MESFET-based amplifier and the SS sensitivity of an AlGaN/GaN microwave HEMT.