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Thomas D. Burd<br />

University of California, Berkeley<br />

17.1 Introduction<br />

© 2002 by CRC Press LLC<br />

17<br />

Dynamic Voltage<br />

Scaling<br />

17.1 Introduction<br />

17.2 Processor Operation<br />

Processor Usage Model • What Should Be<br />

Optimized? • Quantifying Energy<br />

Efficiency • Common Design Approaches<br />

17.3 Dynamically Varying Voltage<br />

Voltage Scaling Effects on Circuit Delay • Energy<br />

Efficiency Improvement • Essential Components<br />

for DVS • Fundamental Trade-Off • Scalability<br />

with Technology<br />

17.4 A Custom DVS Processor System<br />

System Architecture • Voltage Scheduler • Voltage<br />

Converter • Measured Energy Efficiency<br />

17.5 Design Issues<br />

Design over Voltage • Design over Varying Voltage<br />

17.6 Conclusions<br />

The explosive proliferation of portable electronic devices, such as notebook computers, personal digital<br />

assistants (PDAs), and cellular phones, has compelled energy-efficient microprocessor design to provide<br />

longer battery run-times. At the same time, this proliferation has yielded products that require everincreasing<br />

computational complexity. In addition, the demand for low-cost and small form-factor devices<br />

has kept the available energy supply roughly constant by driving down battery size, despite advances in<br />

battery technology that have increased battery energy density. Thus, microprocessors must continuously<br />

provide more throughput per watt.<br />

To lower energy consumption, existing low-power design techniques generally sacrifice processor<br />

throughput [1–4]. For example, PDAs have a much longer battery life than notebook computers, but deliver<br />

proportionally less throughput to achieve this goal. A technique often referred to as voltage scaling [3],<br />

which reduces the supply voltage, is an effective technique to decrease energy consumption, which is a<br />

quadratic function of voltage; however, the delay of CMOS gates scales inversely with voltage, so this<br />

technique reduces throughput as well.<br />

This chapter will present a design technique that dynamically varies the supply voltage to only provide<br />

high throughput when required, as most portable devices require peak throughput only some fraction of<br />

the time. This technique can decrease the system’s average energy consumption by up to a factor of 10,<br />

without sacrificing perceived throughput, by exploiting the time-varying computational load that is<br />

commonly found in portable electronic devices.

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