Julio A. Lonac

Accurate EM-Based Modeling of Cascode FETs

Cascode field-effect transistors (FETs) are widely used in the design of monolithic microwave integrated circuits (MMICs), owing to their almost unilateral and broadband behavior. However, since a dedicated model of the cell is rarely provided by foundries, a suboptimal description built by replicating the standard foundry model for both the common source and common gate device is often adopted. This might limit the success of the MMIC design at the first foundry run. This paper describes an electromagnetic-based empirical model of cascode cells, covering topics from the formulation and identification procedures to the corresponding validation described in an exhaustive experimental section. A MMIC low-noise distributed amplifier case is then presented and the proposed model is used for circuit analysis and instability detection. Clear indication is provided about the improvement in the prediction of critical behaviors with respect to conventional modeling approaches. A cascode cell with a symmetric layout is also successfully modeled.

12-W

The chip-set for the transmitting power lineup of satellite SAR antenna T/R modules has been designed and implemented exploiting a 2- μm GaInP-GaAs heterojunction bipolar transistor (HBT) technology suitable for space applications. The HBT technology features an integrated emitter ballast resistor that enables high-power density operation without suffering thermal runaway phenomena. Two monolithic microwave integrated circuit (MMIC) driver amplifiers and a MMIC HPA are described: the drivers exhibit small-signal gains exceeding 21 dB and P1 dB output power of about 28 and 29 dBm, respectively, in a 2-GHz bandwidth and CW condition. The HPA delivers more than 40-dBm power at about 2.5-dB gain compression and power-added efficiency (PAE) exceeding 36% in a 700-MHz bandwidth in pulsed operation. Its peak performance at the center of the band are 40.9-dBm output power and 45% PAE. These performance are obtained within tight de-rating conditions for space applications.

X

An original empirical approach to deal with nonlinear dynamic thermal effects in electron devices is proposed. The new technology-independent approach is very compact and easy to implement in computer-aided design tools. Therefore, it can be easily coupled with electrical device models in order to obtain accurate electrothermal models that are suitable for nonconstant-envelope RF applications (e.g., pulsed radar). Model equations and identification procedures are derived in this paper. Validation results and comparison with simplified models are also presented both for a simulated field-effect transistor device, as well as for a real hetero- junction bipolar transistor device.

-Band MMIC HPA and Driver Amplifiers in InGaP-GaAs HBT Technology for Space SAR T/R Modules

A nonlinear empirical model is here adopted to model the cold-FET behaviour of a GaAs PHEMT, in the framework of a resistive mixer application. The model, purely mathematical and technology independent, is suitably identified in the device operative region of interest and is validated in large-signal conditions by exploiting a measurements setup based on LS-VNA.

Compact Empirical Modeling of Nonlinear Dynamic Thermal Effects in Electron Devices

In the context of the European Union TARGET Network of Excellence (NoE) a specific interest has been oriented to the comparison of different electron device models in order to choose the most suitable for a particular application (e.g. highly linear amplifiers, low phase noise oscillators). To this purpose different metrics have been defined to compare the models behavior under different operating conditions (i.e. dc, ac small-and large-signal). In this paper we apply different metrics proposed under the TARGET NoE in order to compare two models, the nonlinear discrete convolution (NDC) model, based on a table-based black-box approach, and the EEHEMT1 model, based on the classic equivalent circuit approach. The goal is to provide a set of practical criteria for carrying on reliable model comparisons.

Accurate Nonlinear Electron Device Modelling for Cold FET Mixer Design

Cascode FETs are widely used in the design of MMICs, owing to their almost unilateral behavior. An accurate model of the cell is indeed necessary in order to achieve good circuit performance estimations. In the literature, the Cascode cell models are usually obtained on the basis of measurements of the entire structure or by a preliminary characterization of the common source elementary cell. However, the different influence of the parasitic network between common source and common gate topologies are not taken into account in the latter case. In this paper, a distributed approach based on EM simulations is adopted for the modeling of the parasitic network of the Cascode cell. The proposed procedure leads to a well conditioned characterization of the intrinsic devices, which can be used for the modeling of both the common source and the common gate transistors. Wide experimental validation is provided in the paper.

Comparison of electron device models based on operation-specific metrics

A simple method for the full characterization of passive n-port microwave monolithic integrated circuit (MMIC) structures using standard two-port vector network analyzer (VNA) measurements is presented. Its main advantages are: it does not require to perform measurements from all the ports of the network, no special calibration procedure is needed, the auxiliary terminations required by the procedure can be integrated at the border of the structure under test with minimal area increase, and it can be easily implemented in commercial CAD software. The method was applied to a nine-port microstrip structure corresponding to the output power combiner and impedance matching network of an X-band MMIC high power amplifier (HPA). The full S-parameter matrix was derived from two-port measurements and compared to the circuit–as well as electromagnetic (EM)-based simulations of the structure.