Tianshi Wang

Robust Passive Macro-Model Generation With Local Compensation

This paper presents a new passivity enforcement technique for linear time-invariant multiport systems generated from tabulated measured or simulated data. Traditional methods based on iterative eigenvalue/singular value perturbation do not guarantee convergence, and the error introduced is sometimes large due to the lack of explicit error control. The key to the new algorithm is to correct passivity violations locally with moderate increase of system size. Since all violations are fixed locally, the impact on system transfer function outside the passivity violating frequency range is minimized. Thus, the convergence issue is avoided and the accuracy degradation due to passivity enforcement can also be minimized. The proposed method is very efficient, as optimization procedures are not required. Experimental results demonstrate its performance.

PHLOGON: PHase-based LOGic using Oscillatory Nano-systems

In this paper we take a fresh look at Goto and von Neumann’s phase-based logic ideas, provide enhancements that can overcome major limitations of their previous implementations. We show that with injection locking serving as the central mechanism, almost any DC-powered, self-sustaining nonlinear oscillator — including electronic, spintronic, biological, optical and mechanical ones — can be used to build fundamental components — including latches and combinatorial elements in a phase logic based computing architecture. We also discuss noise immunity and potential power dissipation advantages that can be achieved under this scheme.

MAPP: The Berkeley Model and Algorithm Prototyping Platform

We describe the Berkeley Model and Algorithm Prototyping Platform (MAPP), designed to facilitate experimentation with numerical algorithms and models. MAPP is written entirely in MATLAB and is available as open source under the GNU GPL.

Design tools for oscillator-based computing systems

Recently, general-purpose computing schemes have been proposed that use phase relationships to represent Boolean logic levels and employ self-sustaining nonlinear oscillators as latches and registers. Such phase-based systems have superior noise immunity relative to traditional level-encoded logic, hence are of interest for next-generation computing using nanodevices. However, the design of such systems poses special challenges for existing tools. We present a suite of techniques and tools that provide designers with efficient simulation and convenient visualization facilities at all stages of phase logic system design. We demonstrate our tools through a case study of the design of a phase logic finite state machine (FSM). We build this FSM and validate our design tools and processes against measurements. Our plan is to release our tools to the community in open source form.

MAPP: A platform for prototyping algorithms and models quickly and easily

The lack of a convenient yet powerful platform for prototyping simulation algorithms and mathematical models has long hindered research and collaboration in continuous-time (CT) simulation and modelling. We present the Berkeley Model and Algorithm Prototyping Platform (MAPP), which aims to make such prototyping and evaluation fast and easy. A key feature of MAPP is modular code structuring, the design of which is strongly influenced by modern, DAE-based formulations for system equations and algorithms. This internal code structuring, which differs markedly from that of Berkeley SPICE and related simulators, enables users to add new simulation algorithms with only minimal knowledge of device models, and vice-versa. Another key feature of MAPP is that it is designed from the ground up to support modelling and simulation multi-physics systems. We illustrate MAPPs implementation of devices and algorithms and present two samples of its use. MAPP has been released as open source under the GNU Public License.

Multiphysics modelling and simulation in Berkeley MAPP

We introduce the newly-developed modules for multiphysics modelling and simulation in Berkeley Model and Algorithm Prototyping Platform (MAPP). Using them, developers can write compact models for not only electronic devices, but also those from optoelectronics, spintronics, microelectromechanical systems (MEMS), etc. They can also connect these device models into systems using multiphysics netlists and run various simulation algorithms on them. In this paper, we explain the key concepts and techniques behind these modules, and illustrate the usage of them through examples. Our plan is to make them available in open-source form as part of MAPP under the GNU Public License.

Domain-Alternated Optimization for Passive Macromodeling

Passivity enforcement is an important issue for macromodeling for passive systems from measured or simulated data. Existing passivity enforcement techniques based on iteratively fixing the passivity either suffer from convergence issue or lack optimality that will sometimes lead to unacceptable error. In addition to the traditional two-stage (fitting plus enforcement) schemes, we propose a postenforcement optimization, which takes a passive yet not necessarily accurate model as the starting point, and performs local search to find the local optimum. A new technique, called domain-alternated optimization is proposed to eliminate passivity constraints while still guarantees strict passivity during the optimization. Experiments show that taking the models generated from existing enforcement methods, the proposed method can provide significant improvement on accuracy. The proposed method is efficient and can deal with problems up to a few tens of thousands of variables.

Modelling multistability and hysteresis in ESD clamps, memristors and other devices

Multistability and hysteresis are widely occurring phenomena in devices, leading to many misconceptions among compact model developers. In this paper, we show how hysteretic devices can be modelled in general using only continuous/smooth primitives in a differential equation format suitable for simulation, and how the models can be implemented properly in languages like Verilog-A and ModSpec (MATLAB®). Apart from the generic formalism, several concrete device examples are described and analyzed, including a new compact model for ESD protection devices, new memristor models, a simplified electro-thermal model for HBTs, and a modified Stoner-Wohlfarth model for ferromagnets. Common features of these models are studied to further illustrate the modelling methodology for multistability and hysteresis in devices.

Poster: MAPP: The Berkeley Model and Algorithm Prototyping Platform

We present the Berkeley Model and Algorithm Prototyping Platform (MAPP), a MATLAB®-based framework for conveniently and quickly prototyping device compact models and simulation algorithms. MAPPs internal code structuring, which differs markedly from that of Berkeley SPICE and related simulators, allows users to add new devices with only minimal knowledge of simulation algorithms, and vice-versa. We describe MAPPs structuring and provide an overview of its capabilities. MAPP is available as open source under the GNU Public License.

An efficient time step control method in transient simulation for DAE system

Adaptive time step control is very important or even crucial in transient simulation for the efficiency of a circuit simulator. Existing methods are mainly based on the formula of the local truncation error (LTE) for solving ordinary differential equations (ODEs), which is an approximation for the circuit simulator solving a system of nonlinear differential algebraic equations (DAEs). In this work, we derived the formula of LTE for DAE system and proposed a new time step control method. Experimental results show that the proposed method works well for industrial circuits.