Lucia Dumitriu

A new steady-state analysis method for RF-IC circuits driven by multi-tone signals

The paper presents a new version of the modified nodal method for analysis of the circuits with widely separated time scales. The key idea is to use multiple time variables, which enable signals with widely separated rates of variation to be represented efficiently. The differential algebraic equations (DAEs) describing the RF-IC circuits are transformed into multi-time partial differential equations (MPDEs). In order to solve MPDEs we use the associated resistive discrete equivalent circuits (companion circuits) for the dynamic circuit elements. The algorithm to formulate and to solve the dynamic modified nodal equations was implemented in a computing program, which constitutes a useful tool for steady-state analysis of a very large class of nonlinear analog circuits

On wireless power transfer

The paper is a general survey on power transfer by induction. The physical principle is pointed out and the constraints for an optimal operation applied both to the emitter and receiver are specified. Couple mode theory is used to study the wireless power transfer and a comparison with the circuit theory results is made. The analysis is focused on the power transfer efficiency in connection with the mutual inductance. An accurate method for mutual inductance computation is presented and the power transfer optimization is performed for different geometrical configurations which involve different mutual inductances.

TIME DOMAIN DIAKOPTIC ANALYSIS BASED ON REDUCED-ORDER STATE EQUATIONS

In this paper we present some new tearing techniques to systematically formulate the state equations in symbolic normal-form for linear and/or nonlinear time-invariant large-scale analog circuits. The excess elements of the first and of the second kind are unitarily treated in order to allow a symbolic representation of the circuit with a minimum number of state variables. A procedure to reduce the state equation number of each subcircuit is also presented. The reduced-order is based on an implicit integration algorithm and on the successive elimination of the selected state variables. Examples are given to illustrate the decomposition procedure, the assignment of the connection sources and the reduced-order technique.

Performance optimization in wireless transfer of electromagnetic energy

The paper presents the performance optimization in wireless power transfer. The power transfer efficiency is selected as objective function and an appropriate frequency space representation is used by means of the desired performance quantity generated in full symbolic form. This is combined with some computations performed on the real system and an optimization algorithm for some scalar and/or vector functions of multiple variables provided by Matlab Optimization Toolbox. The algorithm is suitable to compute the optimal circuit parameters which guarantee the maximum value of the performance quantity. The paper also highlights some aspects regarding the conditions that have to be fulfilled by a power supply system that uses wireless technologies, for an optimal transfer of energy. The proposed optimization technique was validated by simulation.

On the time-domain analysis of analog circuits containing nonlinear inductors

The paper proposes effective solutions to include nonlinear inductors with soft ferromagnetic core in the time-domain circuit analyses. Three inductor models are developed, tested and compared. They are conceived for different degrees of accuracy related to the real devices. The models are robust and reliable due to the modeling concept that avoids numerical instabilities. An enhanced inductor model can serve to numerical analyses aiming the optimization of some constructive parameters (as the airgap length or number of turns). A SPICE implementation was performed and exemplified for different operation conditions.

Tolerance analysis for Chebysev filters

The paper presents two methods for analyzing analog circuit tolerances. Both methods were applied to a low pass and a high pass Chebyshev filter. One method called Monte Carlo analysis relies on the circuit matrix for generating results; the other called fast Monte Carlo analysis uses the circuits transfer function in order to generate the results of the tolerance analysis. The circuits elements sensitivities are calculated using the derivates of the circuits transfer functions.

A new approach to the computation of reduced order models for one-port and two-port RC circuits

A method for the computation of a reduced order circuit model, based on the approximation of |Y(jomega)| with a set of assymptotes corresponding to a simple RC admittance is presented. The circuit passivity is preserved unlike the majority of other approaches. A 1033 node RC circuit is reduced to admittance with one pole and two zeros for a frequency range of three decades

Sensitivity analysis of analog circuits based on a modified nodal approach

The paper presents an improvement of sensitivity analysis methods of analog lumped circuits. A practical and reliable approach has been developed and implemented in a computation program intended for linear and/or piecewise-linear approximation of the nonlinear RLCM circuits containing any type of passive elements, independent and controlled sources. A powerful modified nodal approach to build the mathematical model combined with some symbolic computation strategies has been exploited, in order to reduce the computational effort and to minimize the numerical errors. The developed software tool is conceived as a useful and valuable support for research and design engineers.

On analog circuit parameter estimation

Our paper presents a new method to estimate the analog circuit parameters based on some measurements performed on the real circuit, the parameters of interest being those which are difficult or impossible to be measured directly. Starting from the equivalent scheme of an analog circuit in sinusoidal behavior, we generate the network function in full symbolic form, obtaining an appropriate frequency space representation based on the complex or Laplace modified nodal equations. The magnitude and the phase of the complex transfer function can be measured by supplying the circuit with a variable frequency sinusoidal voltage. Using the measured parameters as reference and the symbolic transfer function computed before, the model parameters of interest are obtained by an iterative identification algorithm based on Output Error method. In this paper are defined two new objective functions which can be minimized using one of the fminimax or fminunc functions from the Matlab toolbox. Both algorithms are based on iterative computation starting from certain initial values, being efficient for less than four estimated parameters. The algorithms are suitable for linear circuits, as well as for small-signal nonlinear circuits. Finally, the proposed estimation techniques were tested and validated on simulation data on an illustrative example.

Model order reduction by a projection technique implemented on state equations

Krylov subspace-based projection methods offer the tools for an efficient simulation of large-scale dynamic systems, preserving stability and passivity of the original circuit. This paper presents a simple and efficient implementation of Krylov projection method on state equations of the circuit. The efficiency comes from the fact that the state equations, in the normal form, work with a minimum number of independent variables, and the effort involved by the transfer function computation is smaller then in the modified nodal equation (semi-state equation) case. We elaborated a new and efficent procedure to formulate the state equationds in the normal form. It is shown that the MIMO systems can be well-handle using this approach. An example is used to illustrate the proposed technique and some conclusions are pointed out.