A Guide to Creating Robust Device Models

Well-Posed Device Models for Electrical Circuit Simulation
A Guide to Creating Robust Device Models
A. Gokcen Mahmutoglu, Tianshi Wang, Archit Gupta and Jaijeet Roychowdhury
March 25, 2017

Synopsis: This document provides guidelines for creating computational device models that work well in simulation. We build our discussion around the mathematical notion of “well-posedness”. We show that the requirements for a model to be well-posed stem from the internal working mechanisms of simulators. Therefore, our main aim is to provide insight into the numerical procedures used by simulators in order to help model developers avoid ill-posedness issues. We start our discussion with an example that shows how an ill-posed Verilog-A model can produce different simulation results in different simulators. We then provide a step-by-step simulation case study. In this case study, we illustrate the role of device models in simulations by examining the steps a simulator goes through, from taking a netlist as input to producing a simulation result as output. Finally, we distill our discussion in a functional definition of a well-posed model. As an extension to our theoretical discussion, we also provide practical guidelines that should be followed by Verilog-A models in order to avoid ill-posedness issues.

This document is published as a part of the Nano-Engineered Electronic Device Simulation (NEEDS) initiative. NEEDS is an NSF-funded initiative whose charter includes the development of tools and techniques for the production of high-quality device models¹:

“NEEDS has a vision for a new era of electronics that couples the power of billion-transistor CMOS technology with the new capabilities of emerging nano-devices and a charter to create high-quality models and a complete development environment that enables a community of compact model developers.

NEEDS Team: Purdue, MIT, UC Berkeley, and Stanford.”

¹For more information about NEEDS please visit https://nanohub.org/groups/needs/
https://nanohub.org/resources/26200/download/well-posed_device_models-29453e4.pdf