Stephen A. Maas

A comparative overview of microwave and wireless power-amplifier behavioral modeling approaches

This paper presents a comparative overview of the most important approaches presented to address the behavioral modeling of microwave and wireless power amplifiers (PAs). Starting from a theoretical framework of recursive and nonrecursive nonlinear filters, it proposes a classification of the various PA behavioral models, discussing their abilities to represent the different effects observed in practical circuits. Using that formal procedure, one explains how it was possible to integrate a wide range of behavioral modeling activities and to show that some of them, which at first glance seemed to be quite different, are, indeed, identical in their modeling capabilities.

A GaAs MESFET Mixer with Very Low Intermodulation

This paper describes the design and performance of a new type of resistive mixer, which uses the channel resistance of a GaAs MESFET to achieve frequency mixing. Because this resistance is highly linear, very low intermodulation results. The mixer can be analyzed via existing mixer theory, with good agreement with measured performance. At 10 dBm LO power, the X-band mixer achieves 6.5 dB conversion loss, 6.6 dB noise figure, 21.5 dBm output third-order intermodulation intercept point, and 9.1 dBm 1-dB compression point.

Modeling MESFETs for intermodulation analysis of mixers and amplifiers

The problem of modeling GaAs MESFETs for calculations of intermodulation and spurious responses is examined. It is shown that an adequate model must express not only the absolute I/V characteristics of the device, but also the derivatives of those characteristics. It is demonstrated that these derivatives are dominant in determining intermodulation levels, and that the common approaches to modeling MESFETs do not model those derivatives very well. Finally, a new model for the MESFET gate I/V characteristic (the dominant nonlinearity in most FETs) that is accurate through at least the third derivative is proposed. >

Two-Tone Intermodulation in Diode Mixers

This paper explores, experimentally and theoretically, the problem of minimizing second- and third-order intermodulation distortion in diode mixers. A numerical technique is presented which can be used to calulate internrodulation levels with unprecedented accuracy, and it is used to identify circuit and diode parameters which maximize dynamic range. It is shown that intermorhdation distortion is minimized by using low diode junction capacitance and series resistance, short-circuit embedding impedances, and high local-oscillator level. It is also shown that certain conditions which may optimize conversion loss, such as image enhancement, may severely exacerbate intermodulation.

How to model intermodulation distortion

The author examines the problem of calculating intermodulation levels and mixer spurious responses in nonlinear microwave circuits. It is shown that, in order to perform such calculations successfully, the expression for the I/V characteristic of the solid-state device must accurately reproduce not only the characteristic itself, but also its derivatives. One must furthermore choose the most appropriate analytical technique and be mindful of the dynamic-range limitations of Fourier transforms, of the need to use an adequate and correct set of frequency components, and finally of the limitations of linear-element models. Ways to obtain accurate analyses of these phenomena using available harmonic-balance and Volterra-series circuit simulators are described.<<ETX>>

A general-purpose computer program for the Volterra-series analysis of nonlinear microwave circuits

A computer program is described that performs a Volterra-series analysis of a weakly nonlinear microwave circuit having an arbitrary topology. The program uses the method of nonlinear currents and a nodal formulation. In this approach, each nonlinear circuit element is described as a linear element in parallel with a set of current sources; each current source represents a single order (greater than one) of the mixing products, and its current is a nonlinear function of the node-voltage components at lower-order mixing frequencies. The weakly nonlinear circuit is reduced to a linear circuit, which contains the linear elements and the linear parts of the nonlinear elements, and a set of excitation sources. The program is intended primarily for use in the design of microwave circuits; its catalog of circuit elements includes the distributed elements necessary for such work. Because the program formulates and solves the circuit equations numerically, the user need not simplify either the circuit or the model of the solid-state device, or make any of the other common simplifying assumptions.<<ETX>>

Novel Miniature and Broadband Millimeter-Wave Monolithic Star Mixers

In this paper, three monolithic star mixers using a new miniature dual balun are proposed. The first one is a double spiral transformer mixer, and the second one is a trifilar transformer mixer. Both of these are fabricated using a commercial GaAs pseudomorphic HEMT process. The third is a 3-D transformer mixer, which is fabricated using a commercial CMOS process. These mixers exhibit bandwidths over 25-45 GHz (57%) with local oscillator isolations better than 20 dB. These star mixers are smaller than (lambda/6timeslambda/6) for the mixer core area. Compared with traditional star mixers, these mixers demonstrate 80% size reduction, and achieve good performance with the smallest chip size among all star mixers using monolithic microwave integrated circuit processes.

A GaAs MESFET Balanced Mixer with Very Low Intermodulation

A new type of balanced resistive mixer has been realized by using the unbiased channel of a GaAs MESFET as the mixing element. Because this resistance is only very weakly nonlinear, very low intermodulation results. State-of-the-art second-and third-order output intercept points of 34 and 21 dBm are achieved, with 7 dB conversion loss at X band.

Design and performance of a planar star mixer

This paper describes the realization of a hybrid star mixer as a planar circuit. The mixer has a minimum conversion loss of 5 dB and, for a conversion loss of less than 9 dB, spans over 2.2 GHz in IF bandwidth and 8 GHz in RF/LO bandwidth. The mixer employs a novel, planar balun structure, similar to conductor-backed CPW, that is suitable for realization as a monolithic circuit. >

Stability analysis for large signal design of a microwave frequency doubler

Microwave circuits such as frequency doublers are notorious for instabilities under parametric variation. The instabilities manifested in the doubler are due to the minority carrier lifetime of the pn junction diode. They are calculated using a simpler stability formulation. A global stability chart is computed using a novel technique called the piecewise stability analysis (PSA) method and found to be in close agreement with the experimental values. These instabilities are characterized by secondary Hopf bifurcations and their eventual breakdown to chaos has been observed. The onset of Hopf bifurcation has been verified both experimentally and numerically.