The Berkeley short-channel IGFET model (BSIM), an accurate and computationally efficient MOS transistor model, and its associated characterization facility for advanced integrated-circuit design are described. Both the strong-inversion and weak-inversion components of the drain current expression are included. In order to speed up the circuit-simulation execution time, the dependence of the drain current on the substrate bias has been modeled with a numerical approximation. This approximation also simplifies the transistor terminal-charge expressions. The charge model was derived from its drain-current counterpart to preserve consistency of device physics. Charge conservation is guaranteed in this model.

BSIM: Berkeley short-channel IGFET model for MOS transistors

This tutorial paper addresses some of the principles and provides examples of concurrent architectures and designs that have been inspired by VLSI technology. The circuit density offered by VLSI provides the means for implementing systems with very large numbers of computing elements, while its physical characteristics provide an incentive to organize systems so that the elements are relatively loosely coupled. One class of computer architectures that evolve from this reasoning include an interesting and varied class of concurrent machines that adhere to a structural model based on the repetition of regularly connected elements. The systems included under this structural model range from 1) systems that combine storage and logic at a fine grain size, and are typically aimed at computations with images or storage retrieval, to 2) systems that combine registers and arithmetic at a medium grain size to form computational or systolic arrays for signal processing and matrix computations, to 3) arrays of instruction interpreting computers that use teamwork to perform many of the same demanding computations for which we use high-performance single process computers today.

Concurrent VLSI Architectures

Circuit simulation programs have proven to be most important computer-aided design tools for the analysis of the electrical performance of integrated circuits. One of the most common analyses performed by circuit simulators and the most expensive in terms of computer time is nonlinear time-domain transient analysis. Conventional circuit simulators were designed initially for the cost-effective analysis of circuits containing a few hundred transistors or less. Because of the need to verify the performance of larger circuits, many users have successfully simulated circuits containing thousands of transistors despite the cost. Recently, a new class of algorithms has been applied to the electrical IC simulation problem. New simulators using these methods provide accurate waveform information with up to two orders of magnitude speed improvement for large circuits. These programs use relaxation methods for the solution of the set of ordinary differential equations, which describe the circuit under analysis, rather than the direct sparse-matrix methods on which standard circuit simulators are based. In this paper, the techniques used in relaxation-based electrical simulation are presented in a rigorous and unified framework, and the numerical properties of the various methods are explored. Both the advantages and the limitations of these techniques for the analysis of large IC's are described

Relaxation-Based Electrical Simulation

Circuit simulation programs have proven to be most important computer-aided design tools for the analysis of the electrical performance of integrated circuits. One of the most common analyses performed by circuit simulators and the most expensive in terms of computer time is nonlinear time-domain transient analysis. Conventional circuit simulators were designed initially for the cost-effective analysis of circuits containing a few hundred transistors or less. Because of the need to verify the performance of larger circuits, many users have successfully simulated circuits containing thousands of transistors despite the cost. Recently, a new class of algorithms has been applied to the electrical IC simulation problem. New simulators using these methods provide accurate waveform information with up to two orders of magnitude speed improvement for large circuits. These programs use relaxation methods for the solution of the set of ordinary differential equations, which describe the circuit under analysis, rather than the direct sparse-matrix methods on which standard circuit simulators are based. In this paper, the techniques used in relaxation-based electrical simulation are presented in a rigorous and unified framework, and the numerical properties of the various methods are explored. Both the advantages and the limitations of these techniques for the analysis of large IC's are described.

Relaxation-based electrical simulation

Methods and apparatus for generating a hierarchical representation of a circuit include obtaining a netlist corresponding to the circuit, the circuit including a plurality of subcircuits. A hierarchical representation of the circuit is then generated from the netlist, the hierarchical representation including the plurality of subcircuits arranged among a plurality of levels of the hierarchical representation. Each one of the plurality of subcircuits has an associated subcircuit definition. In addition, each of a plurality of subsets of the subcircuits share a same subcircuit definition, where memory storage for the same subcircuit definition is shared by the subcircuits in each of the subsets. Moreover, each one of the plurality of subcircuits has a dynamic voltage state. Selected ones of the subcircuits in each of the plurality of subsets share a same dynamic voltage state, where memory storage for the same dynamic voltage state is shared by the subcircuits in each of the selected ones of the plurality of subsets. Once generated, the hierarchical representation may be used during simulation of the circuit to reduce the number of computations required.

Transistor level circuit simulator using hierarchical data

The electrical circuit simulation of large integrated circuits is very expensive. New relaxation-based algorithms promise to reduce this cost by exploiting the properties of large networks. However, this speed improvement is not sufficient for the cost-effective analysis of very large circuits. While array processors have helped inprove the performance of circuit simulators, further improvement can be achieved by the use of special-purpose multiprocessors. In this paper, the implementation of a relaxation-based circuit simulation algorithm, called Iterated Timing Analaysis, on a multi-processor is described. Initial results indicate that this approach has a great deal of potential for reducing the cost of circuit simulation.

A Multiprocessor Implementation of Relaxation-Based Electrical Circuit Simulation

The FTl2 system described in this paper is an interactive system for specifying concurrent digital systems and analyzing their behavior. FTl2 differs from other behavioral-level simulation systems in that the input specification for a circuit is a concurrent program. Specifications are incrementally compiled into augmented dataflow graphs which are then interpreted by a software dataflow machine. FTl2 includes special control structures for describing concurrent behavior in a structured fashion, a number of user-oriented input features, and an extensive macro facility. The concept of nonsharable resources is used to determine timing-dependent module access conflicts in a value-independent manner. Incomplete specifications can be emulated and can be modified interactively. Ftl2 has been implemented in LISP, and is currently operational. 13 references.

J. T. Deutsch

Papers

A Multiprocessor Implementation of Relaxation-Based Electrical Circuit Simulation

Data-flow based behavioral-level simulation and synthesis