Since its beginnings in the early 1970s, the design automation industry has climbed up the complexity scale in the semiconductor world. The design process has seen a steady progression in its automation along the way, with each step overcoming some design issue while also spawning even greater complexity and new challenges. Business models have come and gone, expansions and contractions have taken place, and the EDA industry now faces another series in the great sea of changes.
Among the key drivers that have pushed evolution in design tools, complexity is most critical. In 1965, Gordon Moore predicted that over the following 10 years, the number of transistors per integrated circuit would double every 18 months. That prediction has held up for 27 years longer than Moore himself forecasted (Fig. 1).
A parade of microlithographic innovations has made today's vastly complex ICs possible in the physical realm. But without the design automation methodologies that have been shaped since Fairchild, Motorola, and Texas Instruments (TI) employed legions of draftsmen to produce layouts for TTL building blocks, today's SoC designers would be out of luck.
Multiple factors have shaped the path of design automation and the ways that it and the design process have influenced each other. Process technology was the most important, followed closely by the availability of increasingly powerful computing resources. Closely coupled to the latter was the dispersal of those resources from mainframes to the engineer's desktop.
Consider how design was approached before commercial design automation existed. "I can still remember using drafting boards and cut rubylith," says Ted Vucurevich, senior vice president and chief technology officer at Cadence Design Systems Inc. "That was the state of the art in the early 1970s." Many IC designs were quite small, essentially comprising TTL MOS building blocks. The entire design process was done literally by hand and, at least at the Big Three of Fairchild, Motorola, and TI, in a completely vertically integrated and proprietary fashion. Any design automation was homegrown.
Wally Rhines, CEO of Mentor Graphics Corp. today, remembers those days from his vantage point as head of the group designing consumer products at TI. Rhines recalls, "TI used its proprietary design resources to set up what was, in effect, a 'productization machine.' They realized that the one who would win in TTL was the one who got the most part types out and qualified and sampled the fastest."
To achieve this goal, TI developed a system to quickly design functions, generate masks, characterize the devices, and market them. According to Rhines, that was called the TI Layout and Edit (TILES) system. Schematics were created by hand and simulated in Spice, a relatively new idea itself.
In 1972, the Spice 1 simulator was released into the public domain by the University of California at Berkeley Group, led by Prof. Donald Pederson. It was quickly seized by the semiconductor companies of the day, which each tweaked and customized it to its liking.
"Verification started with Spice and other applications like it," says Raul Camposano, chief technology officer at Synopsys Inc. "They realized that you could simulate electrical circuits to a great degree of accuracy, which would help a lot in constructing them and making sure they would work the first time."
In those early days, TI and others ran their simulations on the IBM mainframes that had become common on corporate campuses. "At its peak, we kept an entire 3090-600 mainframe running just simulations for semiconductors at one point. It was that big a deal," Rhines says.
Another piece of the automation puzzle from the early 1970s was the emergence of dedicated CAD systems from vendors such as Applicon and Calma for mask production. Automated pattern generation came into vogue as designs grew larger. "People realized you couldn't do these designs by hand anymore, just by drawing them and cutting the rubylith," says Camposano. "It would be much more flexible to have a database in which you could store the patterns. You'd have a digitizing system and to make a change, you could just go into the database and change it."
At TI, the capture process largely took place on proprietary systems, but some moved over to the Calma system based on Data General 32-bit minicomputers. These systems had dedicated operators called layout people. Rhines recalls a clear division of labor where engineers performed circuit design and simulation, but the draftsmen did layout.
Then, technicians would digitize the design from a version drawn on draft paper, using a handheld interface that would enter the coordinates for each of the geometric patterns into the Calma database. Of course, this created significant opportunity for error.
What we now know as physical design verification consisted of taking flatbed plots of the layouts, pinning them on the wall or laying them on a light table, and having people try to find errors. Hence, physical verification was one of the first businesses to be adopted in the emerging custom design space (see "The More Things Change, The More They Stay The Same,").
By the late '70s and early '80s, the practice of using mainframe computers for engineering began to break down. The Applicon and Calma workstations had arrived on the mask-generation side. Next to seeing a computing change was simulation and verification, with the introduction of Apollo workstations and the VAX and Data General systems. "As the engineers tried to use the IBM mainframe, they found that during the last two weeks of the quarter, they didn't get any work done because the corporate financial people were trying to do the close," Rhines says.