An overview of technology, architecture and CAD tools for programmable logic devices

Before the advent of programmable logic devices (PLDs), most digital hardware designs included significant numbers of small-scale integrated (SSI) circuits that comprised basic logic gates and flip-flops. However, modem designs contain virtually none of these low-density parts, but instead are built from more complex devices that consist of an uncommitted array of logic gates and memory elements that can be configured by the user to implement different circuits. The term programmable logic device is not easy to define because the assortment of chips that fall within this broad category, namely any integrated circuit that is programmable by the end user and intended for implementing hardware, has grown very large over the past few years. In fact, even the relevant terminology has become nebulous because of rapid technology changes and the introduction of new innovative architectures. The purpose of this paper is to provide an overview of programmable logic devices in order to present the reader with a clear view of what is available on the market today. The fundamental technologies employed to manufacture PLDs are presented, after which for each of the three categories of chips, namely simple programmable logic devices (SPLDs), complex programmable logic devices (CPLDs), and field-programmable gate arrays (FPGAs), the paper describes the most significant architectural features, examples of applications, and the CAD tool design now typically used when implementing circuits