TABLE OF CONTENTS The design and verification of analog, mixed-signal and mixed-technology systems can be difficult and complex. The process of top-down design for these types of systems is less straightforward than for digital systems. In this chapter we discuss how to use subsystem models with different abstraction levels to answer system-level questions, make system-level trade-offs, verify system performance and discover problematic interactions. We focus on the design process and the role played by VHDL-AMS models.
Top-down design methodologies have had a profound impact on digital system design. They allow us to quickly and efficiently specify, design, synthesize and verify designs ready for fabrication. The key to these methodologies is synthesis, which relies on a mapping between the logical functions we use in a design and the physical circuits that realize the functions. Synthesis technology allows us to work at higher levels of abstraction and to delegate physical implementation details to automatic tools.
The number of digital building blocks required for synthesis is relatively small. Most digital designs can be implemented with a handful of basic logical gates (for example, and, or, not, nand, nor and xor gates) and storage devices (for example, registers, flipflops and latches). The same cannot be said for analog, mixed-signal and mixed-technology designs. The building blocks for these design domains are far more numerous and sophisticated. Furthermore, their behavior cannot be captured as readily as that of digital building blocks. Nonetheless, a methodical top-down design approach is appealing.
Unfortunately, analog synthesis technology is very much...
