Carver Mead (CalTech Professor) – My First Chip (Oct 2017)

Chapters

Abstract

Revolutionizing Integrated Circuits: Carver Mead’s Pioneering Journey

In the annals of technological evolution, few narratives are as compelling as Carver Mead’s journey in revolutionizing integrated circuit design. From his early insights inspired by Moore’s Law, through the challenges of designing complex systems, to his groundbreaking contributions to Very Large Scale Integration (VLSI) and the development of the Programmable Logic Array (PLA), Mead’s work has been a cornerstone of the digital revolution. This article explores the key milestones in Mead’s career, emphasizing his innovative approach to chip design, his inspiration from the aerospace industry, and his lasting impact on modern computing and chip design education.

Moore’s Law and the Dawn of Integrated Circuits

Gordon Moore’s 1965 observation, later coined as Moore’s Law, revealed the potential for exponential growth in transistor density on integrated circuits. Gordon Moore showed Mead a plot of the number of transistors on integrated circuits over time, revealing a consistent doubling trend. Moore extrapolated this trend, predicting that making transistors smaller would lead to more powerful and efficient chips. This insight, brought to Mead’s attention, marked the beginning of a new era in computational power and miniaturization, setting the stage for Mead’s pioneering work.

Scaling and the Physics of Moore’s Law

Mead’s investigation into the physics of Moore’s Law uncovered the benefits of miniaturization: lower voltages, reduced power consumption, and faster operational speeds. Mead calculated that shrinking gate oxides below 50 angstroms would cause electron tunneling, potentially hindering further miniaturization. This understanding was crucial in scaling integrated circuits and set the groundwork for their exponential advancement. He discovered that scaling down voltage proportionally with device size led to faster, more power-efficient devices. This “figure of merit” for computation improved exponentially with scaling, creating a promising path forward for integrated circuits.

Design Challenges and the Hewlett Packard 9100 Inspiration

As integrated circuits grew more complex, Mead faced the challenge of designing systems with millions of transistors. The Hewlett Packard 9100 calculator, an engineering marvel, inspired him with its blend of scientific computation, programmability, and user-friendly design, fueling his vision for the future of computing. Barney Oliver, a Caltech alumnus, showcased Hewlett Packard’s latest calculator, highlighting its advanced features and potential as a desktop tool. Mead envisioned a future where similar devices would be widely accessible.

Teaching Digital Logic and Textbook Genesis

Mead’s passion for education led to a course on digital logic, introducing students to digital system design techniques. His collaboration with Richard Willis resulted in a seminal textbook, becoming a keystone in digital design education and shaping future chip designers. The course focused on understanding the principles of digital logic and designing circuits for specific functions. Mead collaborated with his teaching assistant, Richard Willis, to create a textbook on digital logic design. The book aimed to provide a solid foundation for designing integrated circuits.

The Genesis of VLSI

Recognizing the potential of VLSI, Mead envisioned a shift in design tools and methodologies to harness its power. This foresight was critical in moving away from traditional design approaches to more advanced, efficient ones. Mead observed Intel’s design process, which involved manual drafting of circuit diagrams and painstaking creation of rubylith masks for each layer of the chip. This process was laborious and limited the complexity of designs. Intel’s design approach was limited to Manhattan geometry due to the manual drafting process. Mead recognized the need for automated design tools to enable more intricate circuit layouts.

Early Challenges in Integrated Circuit Design

The initial phase of integrated circuit design was labor-intensive, involving manual creation of circuit diagrams and transfer onto mylar sheets. This cumbersome process underscored the necessity for automated and efficient design methods. Mead was driven by a desire to create and design precision patterns. He recognized the limitations of existing methods and believed there had to be a better approach. He explored how the aerospace industry created precision printed circuit boards for aircraft and rockets. He discovered the use of Gerber plotters and Gerber code for creating precise patterns.

Manhattan Geometry and the Coordinograph

Integrated circuits’ fabrication constraints led to the adoption of Manhattan geometry, necessitating tools like the coordinograph for precision in designing and cutting rubylith sheets. This method illustrated the complexity and precision required in early chip design.

Innovation from the Aerospace Industry

Mead discovered the use of Gerber plotters in the aerospace industry, which were instrumental in creating circuit boards. This discovery led to renting Gerber plotters for his work, bypassing the need for traditional design tools and introducing him to programmable design methods. Mead encountered a Gerber plotter, an old machine with individual transistors on circuit boards. He realized the significance of using the latest technology to create the next generation of technology. He used a program to create precise patterns for integrated circuits, eliminating the need for manual processes and teams of people. The Gerber plotter produced artwork with contact pads, metal layers, and drivers for connecting wires to internal integrated circuits.

The Development of the Programmable Logic Array

Mead’s encounter with the Gerber plotter was pivotal, leading to the invention of the PLA. He recognized the need for a more regular and structured approach to digital functions, beyond random logic with NAND, NOR gates, and flip-flops. He collaborated with a bright student, Steve Colley, to generate artwork and create a logical program from the input. Mead, along with two others at Texas Instruments and Hewlett Packard, independently invented the programmable logic array (PLA). This concept allowed for the creation of a simple, regular arrangement that could generate any logic function.

Demonstrating the Chip’s Versatility

Mead’s first chip, designed as a general-purpose device, was showcased as a 12-hour clock. This demonstration not only proved the chip’s functionality but also emphasized the structured design approach, pivotal in creating complex designs with assured functionality.

Test and Results:

Mead’s first integrated circuit clock chip was packaged and tested in a similar manner to how he did in 1971. The chip could drive the signals on a fluorescent tube to display the time without external drivers. He hooked up the digit and segment lines to the tube using a prototype board.

Scope Trace:

The purple trace on the oscilloscope represented the A segment of the display. The A segment would be on for all digits except 1, 2, 3, and 4, which have different segment combinations.

Chip Function:

Mead demonstrated the chip’s function by manually changing the time to 9:59 and observing that it correctly rolled over to 10:00, including the correct display of the digits and segments. The chip also correctly transitioned from 12:59 to 1:00 instead of 0:00, as expected for timekeeping.

Realization and Significance:

Mead realized that he had a method of generating VLSI designs that worked reliably due to their structured approach. This led to a shift from focusing on physics to a systematic transformation from idea to architecture, logic structure, programming, and physical realization on silicon. This marked the beginning of Mead’s journey in teaching design of complex integrated circuits and establishing a leading position for his institution in this field.

Impact and Legacy

Carver Mead’s journey in integrated circuit design not only revolutionized the field but also laid the foundation for modern computing. His structured approach to VLSI design has been instrumental in the development of sophisticated circuits, impacting various industries. Moreover, his contributions to education have trained generations of students, cementing his legacy as a pivotal figure in the technological evolution.

In conclusion, Carver Mead’s pioneering steps, from grasping the implications of Moore’s Law to innovating with the PLA and VLSI, have indelibly shaped the landscape of digital technology. His story is not just one of technological breakthroughs but also of inspiring vision, relentless innovation, and lasting impact on both the industry and academia.

Notes by: datagram