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Analog tools require reinvention

Posted: 16 May 2008 ?? ?Print Version ?Bookmark and Share

Keywords:analog ICs? analog designs? register-transfer-level? mixed-signal devices? digital IC design?

Until recently, the majority of ICs were either purely digital or purely analog in nature. Today, to satisfy cost, size, weight and power consumption requirements, sophisticated combinations of analog and digital functions are being implemented on "mixed-signal" devices.

Although conventional analog design and verification tools have evolved in capacity and performance over the years, their underlying fundamental architectures are still largely based on mid-1990s technologies. Unlike their digital counterparts!which have evolved to provide a high level of automation, resulting in tremendous increases in designer productivity!analog tools support minimal automation, and analog designs are still largely handcrafted, a process that is time-consuming and prone to error.

Quick history
In the early days of digital IC design!about early 1960s!schematic diagrams were hand-drawn using pen, paper and stencils (or the occasional restaurant tablecloth). The diagrams showed the symbols for the logic gates and functions that were to be used to implement the design, along with the connections between them.

Similarly, the drawings representing the structures used to form the transistor logic gates and interconnects were done by hand. These drawings!which were formed from groups of simple polygons!were subsequently used to create the photomasks, which were themselves used to create the actual silicon chip.

The first level of digital design automation, emerging in the early to mid-1970s, involved gate-level schematic capture, event-driven simulation, and automatic place and route. In the late 1980s and early 1990s, designers started to move to a higher level of abstraction. Logic synthesis technology could be used to translate a register transfer level (RTL) representation into a corresponding gate-level netlist. Designer productivity increased, and the combination of RTL and logic synthesis allowed digital designs to be easily migrated to a new foundry or process node.

More recent tools, such as Magma Design Automation's Talus environment, can automatically take a digital design from RTL to tape-out in two days or less, irrespective of the size of the design.

Magma Design Automation's Talus environment can automatically extract bridge-fault candidates from the layout.

Handcrafted designs
In the early days of analog system design, circuits were likewise crafted by hand. Transistor-level circuit diagrams were drawn using pen and paper. For designs created out of discrete (individually packaged) components such as transistors, resistors, capacitors and inductors, it was common to build a physical prototype of the design, put it on the testbench, measure real-world values to determine how well it performed, and then tweak component values and add or remove components as required to achieve the desired effect.

Respinning an IC design, however, is very expensive. Thus, in the late 1960s and early 1970s, several universities and commercial companies started developing analog simulators. The programs allowed students and engineers to emulate the operation of an analog circuit without having to build it first. Perhaps the most famous of the early simulators was Spice, which was developed by the University of California at Berkeley and was made available for widespread use in the early 1970s.

Evolution of simulation
Analog simulation has evolved dramatically over the years in terms of the sophistication of the underlying models and algorithms, as well as the capacity and performance of the simulation engines. Nonetheless, most of today's analog tools were conceived in the early and mid-1990s. Their underlying architectures were never intended to support the sophisticated demands of a mixed-signal design environment.

Perhaps more important, today's analog design and verification tools are essentially limited to capturing and simulating transistor-level schematics. Thus far, there has been limited success with regard to automation, and migrating an existing design to a new foundry or technology node effectively requires the circuit to be re-implemented from the ground up.

Talus' automated macro placer flow with underlying register-transfer level synthesis and optimization technology enables rapid exploration of the physical design space with handoff to the physical implementation flow.

Truly mixed
First, all of the analog and digital design and verification engines in a true mixed-signal environment should employ a unified database. To satisfy the demands of today's high-end mixed-signal designs, this solution must obviously provide extreme capacity and performance, such as loading the entire database in a minute or less and redrawing all of the analog and digital layers in seconds. At the full-chip level, the environment must support automatic global routing for the chip-finishing stage of the design; also, the system must support full-chip mixed-signal extraction and simulation.

Next, analog design tools must be enhanced to provide automation and productivity capabilities similar to their digital counterparts!for example, the ability to specify an analog function at a high level of abstraction and then automatically synthesize that representation into its transistor-level equivalent, and to perform analog refinement and optimization.

Finally, it will be necessary to automate the migration process for an analog design from one process technology node to another and from one foundry to another.

We are quickly approaching a crisis with regard to our ability to design large, complex mixed-signal devices in a timely manner. Designers of mixed-signal silicon chips need these capabilities, and they need them now.

- Ashutosh MauskarVP of Product and Business Development
Custom Design Business Unit
Magma Design Automation

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