SICs) economically viable in consumer electronics. The one-time cost of design and preparation for manufacture is huge, whereas the unit pro- duction cost is typically very small. Designers agonize over tiny part cost differences when those differences are multiplied by tens of millions of mobile telephones. As we have said, battery power for a given size and weight has been a dominant dri- ver of cell phone design until recently. It will continue to be a driver, but the trend of the use of that battery improvement is already shifting. Cell phones have become small and light enough to satisfy most users, and the keypad is now more a factor in limiting size reduction than the battery. As a result, the competition is now moving toward in- creasing battery life at the current size. Some phones can run 3 or 4 days of reasonably heavy use without recharging, and it would not be surprising if phones that only need to be recharged once a week become common in the next few years. 7That same large system may have fewer subscribers who use their cellular telephones more heavily. In that case, the mobile telephone fraction of the total cost would be much smaller than two-thirds. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. The User Terminal Key Radio Concepts One technology that may be used to increase battery life is rather remarkable. Philips Electronics has developed a pager that operates on an asynchronous processor chip, a chip without an internal clock. Nearly every commercially sold processor chip since the dawn of computing has had a quartz-crystal timer setting the chip speed. However, there is an alternate design: an asynchronous chip in which the clock func- tion is replaced by a communications function that allows one part of the chip to tell another part when a calculation is complete. Asynchronous chips require radically dif- ferent de