Field-Programmable Gate Arrays: Reconfigurable Logic for Rapid Prototyping and Implementation of Digital Systems

3.1   BACKGROUND TO THE FPGA CONCEPT

3.1.1   History

During the 1960s digital systems were built from small-scale integrated circuits and transistors interconnected on a printed circuit board (PCB). These transistor–transistor logic (TTL) components were small enough that their functions were applicable to almost all digital designs (e.g., it is hard to think of a digital system that could not make use of a 7400 quad NAND gate). This meant that it was commercially attractive to provide a library of such components that were electrically compatible and could be connected to build the target system. As the number of transistors per chip increased, manufacturers realized they had a problem on their hands: the so-called “part-number” problem. With increasing transistor count, logic parts became more specialized and hence usable in fewer systems—for example, an LSI part like the 74LS275 Wallace Tree Multiplier is not useful in most systems. At the same time, the design and manufacturing cost of the parts increased with transistor count. For this reason catalog logic families stalled at the LSI level. Newer structures were required to take advantage of VLSI—there were three approaches:

1. Microprocessors/memories: Microprocessors and memory chips are attractive to the component manufacturer as catalog items since they can be used for programmable systems resulting in high volume sales. However, microprocessors are fundamentally unsuited to many traditional logic applications where instantaneous ...