Unified DC/small-signal/large-signal microwave device modeling and circuit optimization

Abstract

<p>This thesis presents an in-depth investigation of microwave FET device modeling and unified DC, small-signal and large-signal computer-aided design of microwave circuits. Advances in microwave FET device modeling are reviewed. The physical, analytical and nonlinear empirical models and their relationship are discussed. A new integrated DC and small-signal FET model parameter extraction approach is presented which simultaneously fits the FET model responses to the DC and small-signal measurements. Detailed formulas are derived to explore the relationship between the nonlinear DC equivalent circuit and the small-signal equivalent circuit linearized at given bias points. A large-signal FET model parameter extraction approach is introduced. The power spectrum responses of the model are calculated employing the newly exploited harmonic balance (HB) technique for efficient nonlinear frequency-domain circuit simulation. State-of-the-art optimization tools are used to fit model responses to corresponding measurements. Special considerations are given to weighting factor assignment which takes into account the wide spread magnitude of the error functions in the optimization. The HB technique for nonlinear frequency domain simulation of microwave circuits is discussed. The formulations of the HB equation, its Jacobian matrix and the related discrete Fourier transformation are described. A new approach for constructing the multiport matrix especially suitable for HB based circuit optimization is presented. The theoretical background of the unified DC, small-signal and large-signal circuit simulation is investigated. Derivations of the inherent consistency between DC/small-signal simulation and general nonlinear HB simulation are presented. A novel circuit design concept is introduced which explores the seamless integration of DC/small-signal and large-signal circuit design with multi-dimensional specifications. Examples of simultaneous DC/small-signal/large-signal FET model parameter extraction and a small-signal broad-band amplifier design are given to demonstrate the concept.</p>