Teaching ASIC design in electrical/electronics engineering technology programs

Journal of Engineering Technology, Fall 2001 by Anwar, Sohail, Guran, Yolanda, Campbell, Eric

Abstract

In the past, Application Specific Integrated Circuit (ASIC) design courses were taught mostly in graduate-level engineering programs. However, over the last decade, elements of ASIC design have been integrated into numerous undergraduate engineering and engineering technology curricula.

This paper provides an introduction to ASIC design and the technologies used for its implementation, describes ASIC design topics taught in undergraduate electrical/electronics engineering technology programs at several U.S. educational institutions, and presents a case study of ASIC design courses taught at the Oregon Institute of Technology (OIT).

Introduction

An Application Specific Integrated Circuit (ASIC) is a circuit that is designed, customized, or programmed for a specific application rather than for a variety of applications.' Most ASICs are categorized as VLSI (very large scale integration).2,3 Examples include an IC chip for a toy horse that walks, an IC chip that manages the interface between memory and a microprocessor used as the central processing unit (CPU) of an engineering workstation, and an IC chip in a weather satellite.

As shown in figure 1, ASICs are grouped into three principal categories, described as follows:

1. A semicustom logic IC is a monolithic circuit that has one or more customized mask layers. Logic designers use CAD software to design the circuit, then send the design to a semiconductor manufacturer for production. Gate arrays are a special type of semicustom logic IC that contains a large number of gates and special logic functions interconnected by metalization. In a gate array, the transistors are prefabricated in an array that is then fixed in position on a given wafer. Logic functions are achieved through a metalization process that interconnects the transistors with metal wires. Typically, a designer selects and interconnects logical elements from a gate array library. Gate arrays are available with the equivalent of over 50,000 logic gates. A linear array is a semicustom logic IC consisting of an array of transistors and resistors that performs the functions of several linear ICs and discrete devices.

2. In custom logic ICs the logic functions are designed and fabricated into a large-scale integration (LSI) circuit. The primary advantage of custom logic is the integration of multiple standard logic functions into one or two custom ICs. However, since custom logic ICs are unique, they require more design time than standard logic systems. Cell libraries, which are logic design blocks that create a predetermined logic function, can be used to reduce the time needed to design a custom IC. Standard cell-- based ASICs are custom logic ICs that use a library of precalculated circuit structures (cells). These unique cells can be placed anywhere on a chip.2 While a gate array cell consists of an array of identical transistors, a standard cell consists of different size transistors that are optimized for the cell's function. This optimization allows the standard cell ASIC to have a smaller and faster cell for a given function. Finally, the full custom logic IC is used for very large IC design projects. This type of ASIC design requires details of devices such as transistors, resistors, and capacitors and, because of the resulting high cost of nonrecurrent engineering and significant IC design expertise, is normally cost effective only when manufacturing ICs in large volumes.

3. Programmable logic devices (PLDs) replace the hundreds of logic chips that perform the interfacing functions among major components in digital logic systems.2 These devices provide the flexibility to produce custom circuits for logic systems without the high cost and extensive development time needed for full custom or semicustom logic ICs. Simple PLDs are called Programmable Arrays of Logic (PALs) or Programmable Logic Arrays (PLAs) and typically contain less than 750 logic gates. A Complex PLD (CPLD) is a hierarchical arrangement of multiple PAL-like blocks. Field Programmable Gate Arrays (FPGAs) are PLDs that offer fully flexible logic arrays and flexible interconnects and require functional placement and routing. Electrically Programmable Analog Circuits (EPACs) are circuits that allow the user to program and reprogram basic analog functions.

ASICs offer many advantages over off-the-shelf devices, including:

* fewer pins on a board

* reduced board space

* reduced power

* reduced heat

* improved performance

* better radiation tolerance

* improved testability

* enhanced reliability

Teaching ASIC Design Courses in Engineering Technology Program

In the past, ASIC design courses were taught mostly at the graduate level, and it was rare to find them in undergraduate engineering and engineering technology curricula. However, in the past few years, the elements of ASIC design have been integrated into many undergraduate engineering and engineering technology programs. To obtain specific information about ASIC design courses taught in undergraduate electrical/electronics engineering technology programs in the U.S., the questionnaire shown in table 1 was developed and sent to all members of the Engineering Technology Division of the American Society for Engineering Education.