Low-Power CMOS Circuits

Technology, Logic Design and CAD Tools

Christian Piguet

• Publisher: CRC Press
• Year: 2018
• Topic: Technology & Engineering
• eBook ISBN:
  9781351836609
• Subtopic: Computer Engineering
• Index: Technology & Engineering

The power consumption of microprocessors is one of the most important challenges of high-performance chips and portable devices. In chapters drawn from Piguet's recently published Low-Power Electronics Design, Low-Power CMOS Circuits: Technology, Logic Design, and CAD Tools addresses the design of low-power circuitry in deep submicron technologies. It provides a focused reference for specialists involved in designing low-power circuitry, from transistors to logic gates. The book is organized into three broad sections for convenient access. The first examines the history of low-power electronics along with a look at emerging and possible future technologies. It also considers other technologies, such as nanotechnologies and optical chips, that may be useful in designing integrated circuits. The second part explains the techniques used to reduce power consumption at low levels. These include clock gating, leakage reduction, interconnecting and communication on chips, and adiabatic circuits. The final section discusses various CAD tools for designing low-power circuits. This section includes three chapters that demonstrate the tools and low-power design issues at three major companies that produce logic synthesizers. Providing detailed examinations contributed by leading experts, Low-Power CMOS Circuits: Technology, Logic Design, and CAD Tools supplies authoritative information on how to design and model for high performance with low power consumption in modern integrated circuits. It is a must-read for anyone designing modern computers or embedded systems.

Part I

Technologies and Devices

1

History of Low-Power Electronics

Christian Piguet

CSEM & LAP-EPFL

1.1	Introduction
1.2	Early Computers
	Power Consumption of Early Computers • Reused Concepts for Low Power
1.3	Transistors and Integrated Circuits
	Invention of the Transistor • Invention of the IC • MOS Transistors • Early Microprocessors • RISC Machines
1.4	Low-Power Consumer Electronics
	First Electronic Wristwatch • Electronic Watches in Japan • Electronic Watches in the U.S.
1.5	The Dramatic Increase in Power
	Low-Power Workshops • Low-Power Design Techniques
1.6	Conclusion
References

1.1 Introduction

Power consumption awareness began worldwide around 1990–1992. Before that, only niche markets required low-power integrated circuits (ICs). Today, every circuit has to face the power consumption issue, for both portable devices aiming at longer battery life and high-end circuits avoiding cooling packages and reliability issues that are too complex.

It was not anticipated that microprocessors would consume 100 watts today and perhaps 300 watts in 2016, as predicted by the International Technology Roadmap for Semiconductors (ITRS). Looking at a 10-year prediction proposed in 1986 (Figure 1.1), the frequency and throughput were accurate as well as the number of transistors based on Moore’s law; however, no prediction was made for power consumption, while a simple calculation would yield 40 watts. If 40 watts had been predicted in 1986, it is conceivable that the awareness about the increase of microprocessor power would have been much better.

Roughly speaking, power was not an issue during the development of microelectronics from the invention of early computers in 1940 and of the transistor in 1947 to the early 1990s; however, many ideas proposed during this period for improving electronic circuits have been rediscovered and reused in the last 10 years, focusing on power consumption reduction [1]. This chapter begins with a brief history of early computers [2,3,4] to continue by the invention of the transistor and of the IC. Besides the mainstream microelectronics evolution, some aspects of low-power consumer applications are also described before the dramatic power increase during 1990–1992.

This first chapter is far from being an exhaustive history of low-power electronics. It contains some flashes on some well-known or ignored events and provides some considerations or interpretations regarding low power. The history of techniques is not of general interest today, even if more and more companies try to tell their own histories within the context of the “good old days.”

FIGURE 1.1 Predictions.

1.2 Early Computers

The first computer architecture, which we owe to Charles Babbage (1791–1871), was a mechanical analytical engine [5]. Although this machine was never completed, the estimated power required would certainly be very high. The first electronic computers or calculating machines were designed with vacuum tubes to significantly improve the speed over electromechanical machines.

1.2.1 Power Consumption of Early Computers

The ENIAC (1944) is generally considered to be the first electronic computer. It was programmed manually by using wires and connections between the execution units; therefore, it was very fast, achieving 100 kHz. Designed by Mauchly (1907–1980) and Eckert (1919–1995), it required 18,000 vacuum tubes and weighed 20 tons, and it was more of a huge calculator than a computer. The power consumption was 150,000 watts.

Such huge power consumption was not the highest achieved for a computer: the Whirlwind, designed by IBM in 1952 for the Semi-Automatic Ground Environment (SAGE) network (75,000 tubes, 275 tons), consumed 750,000 watts.

The introduction of transistors in the design of computers, although not really aiming at power reduction, nevertheless achieved a significant decrease of their power consumption. A transistor consumes roughly 1000 times less than a vacuum tube. Among the first transistorized computers, the TX0 designed by the Lincoln Laboratory in 1957 was an 18-bit machine containing 3500 transistors and consuming 1000 watts; however, huge mainframe computers still consumed a very large amount of power. For instance, the IBM 360 Model 91, announced in 1964, consumed a significant fraction of 1 MW [9]. The 12-bit PDP 8 minicomputer from Digital, designed in 1965, consumed 780 watts.

1.2.2 Reused Concepts for Low Power

Many concepts and ideas have been introduced for the design of early computers. Some of these ideas were rediscovered recently and used to reduce the power consumption of systems on chip (SoC). For instance, instruction formats of the early computers [6] were based on one-word instructions that could be read in one step or one clock cycle. This is much more energy efficient than the multi-byte instruction formats so common in Complex Instruction Set Computers (CISC) microprocessors. Multi-byte instructions require several memory fetches as well as program counter updates that consume much power. It is quite interesting that the first computers were all designed with Reduced Instruction Set Computers (RISC)-like instruction sets.

FIGURE 1.2 Baby Computer of Manchester University, the world’s first stored-program computer, running for the first time on June 21, 1948. (From the University of Manchester, Manchester, U.K. With permission.)

Another “low-power” feature is the Harvard architecture, which comes from the name of the Harvard Mark I, designed in 1939 by Howard Aiken (1900–1973). This architecture is well-known today for providing two separate data and instruction memories, contrary to the “Von Neumann architecture” that contains only one memory (or a unified cache memory) for both instructions and data [7,8]. It results in a high sequencing of instruction execution (and a large number of clocks per instruction [CPI]), as successive instruction and operand fetches have to be performed. Today, it is well-known that this higher sequencing significantly increases power consumption.

The same applies for bit–serial architectures used for the first computers (e.g., EDVAC, Ferranti Mark I), due to the use of serial delay line memories. Consequently, many clock cycles were necessary to execute a single instruction [10]. A few years later, however, bit–parallel architectures (e.g., Von Neumann’s IAS) featured a much simpler control unit and a reduced sequencing, although the execution unit was more complex. Such an observation is also valid for low power; a higher sequencing always results in larger power consumption.

Pipelined computers were introduced in the 1960s. For instance, the well-known IBM 360 Model 91, announced in 1964, was the first 360-pipelined computer with 20 stages. For scientific code, the number of clocks per instruction was about 1 (CPI = 1). Such a low CPI is very beneficial for reducing power consumption (see Section 1.5). Superscalar and parallel architectures were also introduced early in the history of computers, for instance, the 1964 CDC 6600, with 10 parallel execution units and the Illiac IV with 64 parallel processors. Parallelism is also beneficial for power con...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• PART I Technologies and Devices
• PART II Low-Power Circuits
• PART III CAD Tools for Low-Power
• Index