Showing papers by "Giorgio Vannini published in 2018"

Technology-Independent Analysis of the Double Current-Gain Peak in Millimeter-Wave FETs

Abstract: This letter is aimed at discovering and analyzing anomalous phenomena affecting millimeter-wave FETs, focusing on a GaN HEMT as a case study. For the first time, we show that the real parts of the impedance parameters can increase and then decrease with frequency, due to the resonance of the extrinsic reactive elements. This resonance may be detected as a peak in the magnitude of the short-circuit current-gain. Such a peak is found to be substantially bias and temperature insensitive and to manifest at frequencies higher than the other current-gain peak (CGP), due to the resonance between intrinsic capacitances and extrinsic inductances, giving origin to the double CGP.

Nonlinear-Embedding Design Methodology Oriented to LDMOS Power Amplifiers

Abstract: In this paper, we apply for the first time the nonlinear-embedding technique to the design of power amplifiers (PAs) based on laterally-diffused metal-oxide-semiconductor (LDMOS) field-effect transistors. Such a design technique is based on setting the transistor load line at the intrinsic current-generator plane, according to well-known theoretical guidelines. Then, the selected operating condition can be transposed at any design frequency at the extrinsic transistor terminals, by means of a model of the device nonidealities, such as the nonlinear intrinsic capacitances and the linear parasitic effects. A harmonically-tuned high-efficiency class-F and a wideband class-AB PAs operating within the FM broadcasting band 88 ÷ 108 MHz based on a 10-W LDMOS are then designed and realized. To definitely assess the validity of the proposed approach for the LDMOS technology, we compare the measured performance on the fabricated PAs with the expected predictions.

A New Study on the Temperature and Bias Dependence of the Kink Effects in S22 and h21 for the GaN HEMT Technology

Abstract: The aim of this feature article is to provide a deep insight into the origin of the kink effects affecting the output reflection coefficient (S22) and the short-circuit current-gain (h21) of solid-state electronic devices. To gain a clear and comprehensive understanding of how these anomalous phenomena impact device performance, the kink effects in S22 and h21 are thoroughly analyzed over a broad range of bias and temperature conditions. The analysis is accomplished using high-frequency scattering (S-) parameters measured on a gallium-nitride (GaN) high electron-mobility transistor (HEMT). The experiments show that the kink effects might become more or less severe depending on the bias and temperature conditions. By using a GaN HEMT equivalent-circuit model, the experimental results are analyzed and interpreted in terms of the circuit elements to investigate the origin of the kink effects and their dependence on the operating condition. This empirical analysis provides valuable information, simply achievable by conventional instrumentation, that can be used not only by GaN foundries to optimize the technology processes and, as a consequence, device performance, but also by designers that need to face out with the pronounced kink effects of this amazing technology.

Assessing GaN FET Performance Degradation in Power Amplifiers for Pulsed Radar Systems

Abstract: GaN FETs have achieved superior performance in the design of microwave power circuits. Nevertheless, the amount of dispersion related to this technology poses severe issues for the correct modeling and characterization of these devices. In this letter, the effects of GaN FET dispersion on the design of power amplifiers (PAs) with dynamic power supply, largely adopted in state-of-the-art high-efficiency pulsed radar transmitters, are discussed. In particular, we propose a technique for evaluating GaN device performance degradation in new-generation PAs that represents an effective alternative to pulsed-RF multiharmonic source/load-pull microwave setups.

An Ultra-Wideband Setup to Monitor Antenna-Impedance Variations in Low-Cost IoT Transmitters

Abstract: In this paper, we present an innovative ultra-wideband setup to detect real-time variations in antenna impedance in transmitters oriented to Internet of Things and 5G applications. The proposed measurement technique is validated by means of multi-tone measurements at microwave frequencies.

Comparison of GaN HEMT Technology Processes by Large-Signal Low-Frequency Measurements

Abstract: In this paper, we discuss the comparison of two GaN HEMT technology processes by means of large-signal low-frequency (LF) measurements. LF load line analysis clarified the increase of output power and drain efficiency resulting from significant improvement of both knee voltage and maximum drain current by a modified technology process. The cross-check on this advantage was carried out by means of commonly adopted high-frequency load-pull measurement setups.

Analysis of Gate-Voltage Clipping Behavior on Class-F and Inverse Class-F Amplifiers

Abstract: This paper describes the influence of gate-voltage clipping behavior on drain efficiency in case of class-F and inverse class-F $(\mathbf{F}^{-1})$ operations under saturated regime. Numerical analysis using a simplified transistor model was carried out. As a result, we have demonstrated that the limiting factor for $\mathbf{class}-\mathbf{F}^{-1}$ operation is the gate-diode conduction rather than knee voltage. On the other hand, class-F PA is restricted by the knee voltage effects. Furthermore, nonlinear measurements carried out on a GaN HEMT support our analytical results.