Evolution of Computer-Aided Digital Design Digital circuit design has evolved rapidly over the last 25 years. The earliest digital circuits were designed with vacuum tubes | Team LiB Evolution of Computer-Aided Digital Design Digital circuit design has evolved rapidly over the last 25 years. The earliest digital circuits were designed with vacuum tubes and transistors. Integrated circuits were then invented where logic gates were placed on a single chip. The first integrated circuit IC chips were SSI Small Scale Integration chips where the gate count was very small. As technologies became sophisticated designers were able to place circuits with hundreds of gates on a chip. These chips were called MSI Medium Scale Integration chips. With the advent of LSI Large Scale Integration designers could put thousands of gates on a single chip. At this point design processes started getting very complicated and designers felt the need to automate these processes. Electronic Design Automation EDA 111 techniques began to evolve. Chip designers began to use circuit and logic simulation techniques to verify the functionality of building blocks of the order of about 100 transistors. The circuits were still tested on the breadboard and the layout was done on paper or by hand on a graphic computer terminal. 1 The earlier edition of the book used the term CAD tools. Technically the term Computer-Aided Design CAD tools refers to back-end tools that perform functions related to place and route and layout of the chip . The term Computer-Aided Engineering CAE tools refers to tools that are used for front-end processes such HDL simulation logic synthesis and timing analysis. Designers used the terms CAD and CAE interchangeably. Today the term Electronic Design Automation is used for both CAD and CAE. For the sake of simplicity in this book we will refer to all design tools as EDA tools. With the advent of VLSI Very Large Scale Integration technology designers could design single chips with more than 100 000 transistors. Because of the complexity of these circuits it was not possible to verify these circuits on a breadboard. Computer-aided techniques .
