Component density

Chapter Component density

Teach Yourself Electricity and Electronics Third Edition Book
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Teach Yourself Electricity and Electronics Third Edition Book

  • CMOSComplementary-metal-oxide-semiconductor (CMOS), pronounced “seamoss” (andsometimes written that way by lay people who have heard the term but never seen it indocumentation), employs both N-type and P-type silicon on a single chip. This is anal-ogous to using N-channel and P-channel FETs in a circuit. The main advantages ofCMOS technology are extremely low current drain, high operating speed, and immunityto noise.NMOS/PMOSN-channel MOS (NMOS) offers simplicity of design, along with high operating speed.P-channel MOS is similar to NMOS, but the speed is slower. An NMOS or PMOS digitalIC is like a circuit that uses only N-channel FETs, or only P-channel FETs. You mightthink of NMOS as batting right-handed, and PMOS as batting left-handed. (Then CMOSis analogous to switch hitting.)New trendsResearch is constantly being done to find ways to increase the speed, reduce the powerrequirements, and improve the miniaturization of digital ICs. The motivation arisesmainly from constant consumer pressure for more sophisticated and portable comput-ers. As the technology advances, you can expect to see notebook (laptop) personalcomputers with more memory and higher working speed. The batteries will also lastlonger, because evolving technologies will consume less current.Component densityThe number of elements per chip in an IC is called the component density. There hasbeen a steady increase in the number of components that can be fabricated on a singlechip. Of course there is an absolute limit on the component density that can be attained;it is imposed by the atomic structure of the semiconductor material. A logic gate willnever be devised that is smaller than an individual atom. Technology hasn’t bumped upagainst that barrier yet.MSIIn medium-scale integration (MSI), there are 10 to 100 gates per chip. This allows forconsiderable miniaturization, but it is not a high level of component density, relativelyspeaking. An advantage of MSI (in a few applications) is that fairly large currents can becarried by the individual gates. Both bipolar and MOS technologies can be adapted toMSI.LSIIn large-scale integration (LSI), there are 100 to 1000 gates per semiconductor chip.This is an order of magnitude (a factor of 10) more dense than MSI.Component density529