In mixed-signal integrated circuits, the analog part of the
design often occupies a small portion of the physical die area
but requires a disproportionately large amount of the design
effort and time.
Today’s analog circuit designers often
use a combination of hand analysis and circuit simulation that was widely available in 1980. There
has been some improvement in efficiency and capability since that time, thanks to the development
of improved user interfaces for software tools, and new capabilities for behavioral, high level, and
mixed signal simulation, but the task of circuit design is still reserved for experience circuit
designers using manual design and layout.
The general goal of Analog Computer Aided Design (ACAD) is to reduce the manual design
and layout time required for circuit design. Improving analytic tools is a first step, and creating inhouse
cell libraries from previous designs is a low tech way to speed circuit development through
design re-use, but more aggressive techniques which result in design information reuse and automated
design synthesis offer greater promise for reducing design time. These ACAD approaches
include analog standard cell libraries and analog synthesis approaches such as circuit synthesis,
layout synthesis, and module generation, and hierarchical design synthesis. For now, some working
definitions of these terms are needed. Analog standard cell approaches consist of a library of
well characterized circuit blocks, which the designer assembles into a full analog sub-system. In
general analog synthesis, an input specification is used to drive a process which creates elements
for meeting the design specification. In circuit synthesis a set of circuit specifications are used to
drive a synthesis process which sizes the circuit elements and devices. In layout synthesis an analog
circuit netlist, including additional information about parasitics, matching, and performance
constraints, creates an appropriate layout.