Continuous Time and Mixed-Signal Simulation in Ptolemy II

This report studies the continuous time and mixed-signal simulation techniques in the Ptolemy II environment. Unlike the nodal analysis representation usually seen in circuit simulators, the continuous time systems are modeled as signal-flow block diagrams in Ptolemy II. This representation is suitable for system-level specification, and the interaction semantics with other models of computation can be easily studied and implemented. The numerical solving methods for ordinary differential equations are discussed from the tagged-signal point of view and implemented in the continuous time domain. The breakpoint handling techniques are essential for performing correct simulation and supporting the interaction with other domains. Mixed-signal simulation of continuous time and discrete event models is discussed. Event detection can be performed using the breakpoint handling mechanism. The coordination of the execution of the two models are discussed. The result shows that when a continuous subsystem is embedded in a discrete event system, the inner system must run ahead of the global time and be able to roll back. Based on the result, a correct and efficient simulation strategy is presented. As a case study, the mixed-signal simulation techniques are applied to a micro accelerometer with sigma-delta kind of digital feedback