Ronald A. Rohrer

Asymptotic waveform evaluation for timing analysis

Asymptotic waveform evaluation (AWE) provides a generalized approach to linear RLC circuit response approximations. The RLC interconnect model may contain floating capacitors, grounded resistors, inductors, and even linear controlled sources. The transient portion of the response is approximated by matching the initial boundary conditions and the first 2q-1 moments of the exact response to a lower-order q-pole model. For the case of an RC tree model, a first-order AWE approximation reduces to the RC tree methods. >

The state-variable approach to network analysis

The universality of the state-variable approach to network analysis is demonstrated in general discussions and specific examples. The method of formulation of the state equations for an arbitrary lumped, linear, finite, reciprocal, passive, time-invariant network is presented fully, while the relaxation of these restrictions is indicated in detail; i.e., the state-variable characterization of active, nonreciprocal, time-variable, and nonlinear networks is discussed. Finally, there is a brief guide of the current research where the state-variable analysis is brought to bear upon certain qualitative aspects of classical and nonclassical network behavior.

Interconnect simulation with asymptotic waveform evaluation (AWE)

The interconnect analysis problem is treated in a general fashion, exploiting the efficiency and accuracy of asymptotic waveform evaluation (AWE) for the linear interconnect portion of the circuit while using the SPICE simulator for the nonlinear portions. An algorithm that allows the use of partitioned circuit solution techniques in conjunction with AWE is described. A special technique for determining the moments of a partition comprising distributed elements is presented. Moment-computation algorithms for AWE are combined with the method of characteristics to form another type of macromodel for systems of coupled lossy lines. The AWESpice algorithm, which combines the linear multiport macromodels of interconnect with general nonlinearities in a time domain simulation, is described. Results of using the techniques are provided. >

AWESpice: a general tool for the accurate and efficient simulation of interconnect problems

AWESpice is a tool for the efficient and accurate simulation of circuits dominated by interconnect. It accepts a general nonlinear circuit and uses the asymptotic waveform evaluation (AWE) algorithm to efficiently convert its linear interconnect portion into multiport admittance macromodels. The macromodels are then simulated in conjunction with the nonlinear devices using a modified version of the SPICE algorithm. This technique leads to a significant reduction in CPU time while retaining the benefits of a conventional circuit simulator. Some examples that have been run to show the accuracy and efficiency of AWESpice on a variety of interconnect problems are presented.<<ETX>>

Computationally efficient electronic-circuit noise calculations

The interreciprocal adjoint network concept is applied to the computer simulation of electronic-circuit noise performance. The method described is extremely efficient, allowing consideration of an arbitrarily large number of uncorrelated noise sources with less effort than for the original small signal a.c. analysis. Because all noise sources may be considered, no a priori assumption need be made as to which noise sources are dominant in a complicated circuit. The method is illustrated with an operational- amplifier example.

Computer analysis of nonlinear circuits, excluding radiation (CANCER)

CANCER is a reasonably general circuit analysis program especially suited to integrated-circuit simulation. The program provides for the analysis of large circuits in the following four modes of operation: nonlinear d.c., large-signal transient, small-signal a.c., and thermal and shot noise. These subanalysis capabilities are intercoupled appropriately for convenience and efficiency. Internally, CANCER is a very general nodal analysis program that derives its efficiency from the exploitation of sparse matrix, adjoint, and implicit integration techniques.

Piecewise approximate circuit simulation

Conventional circuit simulation methods are inflexible and slow, especially for large circuits. Piecewise approximate circuit simulation, an alternative that can be more efficient and allows variable accuracy in the simulation process, is discussed. Thus, the tradeoff between accuracy and CPU time is in the hands of the user. SPECS (simulation program for electronic circuits and systems) is the prototype implementation of a piecewise approximate, tree/link based, event driven, variable accuracy circuit simulation algorithm that uses table models for device evaluation. The models can be built at various levels of accuracy, and concomitant levels of precision are reflected in the simulation results. SPECS has been benchmarked on some large, industrial circuits and has proven to be an efficient and reliable simulator. However, it suffers a penalty in run time while simulating stiff circuits, or circuits with a wide range of time constants. The authors present enhanced algorithms used in SPECS to ensure efficient steady-state computation for stiff circuits. >

Adaptively controlled explicit simulation

Adaptively Controlled Explicit Simulation (ACES) is a timing simulation methodology for the verification of the transient behavior of integrated circuits. A new adaptively controlled explicit integration approximation is used that overcomes stability problems encountered in earlier explicit techniques. Circuit partitioning is employed, which allows event driven simulation and exploitation of circuit latency. Piecewise linear models are used for nonlinear devices, allowing efficient simulation of MOS, bipolar, and BiMOS circuits. Simulation accuracy in ACES can be varied by controlling the accuracy of either the integration approximation or the piecewise linear device models. With the combination of generality, exploitation of circuit latency, and ability to vary accuracy effectively, ACES provides an efficient environment for transient simulation of integrated circuits and systems. >

AWEsim: a program for the efficient analysis of linear(ized) circuits

Asymptotic waveform evaluation (AWE) is a novel method to analyze linear(ized) circuits. It uses a form of Pade approximation rather than numerical integration to approximate the behavior of linear(ized) circuits in either the time or the frequency domain. Improvements are presented to the theory of AWE to avoid some inherent limitations of Pade approximation. A discussion is presented of the practical aspects that have arisen in the attempt to use AWE in a simulation program called AWEsim. Results are also presented of AWEsim that clearly demonstrate the advantage of AWE over traditional approaches to circuit simulation.<<ETX>>

Sensitivity considerations in optimal system design

The sensitivity of a control system is usually taken to be the normalized variation of some desired characteristic with the variation of plant or controller parameters. Rather than the usual absolute sensitivity described above, a new definition of relative sensitivity is introduced for the optimal control problem, wherein the system performance is always compared with its optimum under the given circumstances. The implications of the relative sensitivity and its relevance to optimal system design are discussed in detail. Moreover, a theoretical approach to the problem of system optimization when plant parameters are subject to change or are incompletely specified is presented.