ASIC DESIGN - INTRODUCTION TOASICs...

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INTRODUCTION  TO ASICs An  ASIC  (pronounced “a-sick”; bold typeface defines a new term) is  an  application-specific integrated circuit  —at least that is what the acronym  stands for. Before we answer the question of what  that  means we first look at  the evolution of the silicon chip or  integrated circuit  (  IC  ). Figure 1.1(a) shows an IC package (this is a pin-grid array, or PGA, shown  upside down; the pins will go through holes in a printed-circuit board). People  often call the package a chip, but, as you can see in Figure 1.1(b), the silicon  chip itself (more properly called a  die  ) is mounted in the cavity under the  sealed lid. A PGA package is usually made from a ceramic material, but plastic packages are also common. FIGURE 1.1 An integrated circuit (IC). (a)  A pin-grid array (PGA)  package. (b) The silicon die or chip is under the package lid.   The physical size of a silicon die varies from a few millimeters on a side to  over 1 inch on a side, but instead we often measure the size of an IC by the  number of logic gates or the number of transistors that the IC contains. As a  unit of measure a  gate equivalent  corresponds to a two-input NAND gate (a  circuit that performs the logic function,  F =A • B  ). Often we just use the  term  gates  instead of gate equivalents when we are measuring chip size—not  to be confused with the gate terminal of a transistor. For example, a 100 k-gate  IC contains the equivalent of 100,000 two-input NAND gates. The semiconductor industry has evolved from the first ICs of the early  1970s and matured rapidly since then. Early  small-scale integration  (  SSI  )  ICs contained a few (1 to 10) logic gates—NAND gates, NOR gates, and so on —amounting to a few tens of transistors. The era of  medium-scale  integration  (  MSI  ) increased the range of integrated logic available to  counters and similar, larger scale, logic functions. The era of  large-scale  integration  (  LSI  ) packed even larger logic functions, such as the first  microprocessors, into a single chip. The era of  very large-scale 
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integration  (  VLSI  ) now offers 64-bit microprocessors, complete with cache  memory and floating-point arithmetic units—well over a million transistors— on a single piece of silicon. As CMOS process technology improves,  transistors continue to get smaller and ICs hold more and more transistors. 
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