TABLE OF CONTENTS Mixed-signal systems include interacting digital and analog subsystems. The digital portions of the system are modeled using variables, signals and processes that execute at discrete time steps. The analog portions of the system are modeled using terminals, quantities and simultaneous statements that represent continuous behavior. In this section, we consider the VHDL-AMS mechanisms that support interaction between the digital and analog portions of the system.
A wide variety of applications require mixed-signal modeling capabilities to accurately represent the system behavior. Digital designs sometimes require mixed-signal modeling of high-performance components for which the digital modeling abstraction is not adequate. Since digital systems are really abstractions of well-behaved analog systems, we can use mixed-signal modeling to explore portions of digital-system behavior in more detail. Other systems are explicitly mixed signal with separate digital and analog parts. For example, chip sets for cellular phones comprise digital signal processors, analog transceivers and converters between the analog and digital portions. Other examples include the sense amplifiers used in memories, input/output pads for chips and clock generation circuitry.
When we wish to simulate a mixed-signal system described in VHDL-AMS, we must consider the mechanism that exchanges data between the digital simulation kernel and the analog solver. Let us first consider the exchange of data from the analog domain to the digital domain.
There are two aspects of the exchange of data from the analog domain to the digital domain: the translation of continuous-valued quantities to digital signals or variables and the...
