Digital Integrated Circuit Design I
Introduction to Full Custom Integrated Circuit Design

Due to the evolution of microprocessors and dynamic memory with their use in personal computers and workstations, at least two applications of the integrated circuit are well known. Integrated circuit design, however, covers a much wider range of consumer products. Machine controllers, guidance systems, cell phones, CD players/recorders and the gambling machines in the entertainment industry; even temperature sensor in your coffee maker at home might employ a custom integrated circuit. ICs provide analog-to-digital/digital-to-analog conversion, digital filtering, state machines for control, etc.

The ELE447 course is an introduction to full custom, digital integrated circuit design. The term full custom means that in this course we are learning to realize logic gates at the transistor level using a layout editor which arranges the mask set used in the IC fabrication. In full custom IC design the designer has complete control over the selection of the logic family, the implementation of the logic cells and the floor plan of the integrated circuit. Because of the efficiency in area utilization and reduced power consumption there are many applications which can only be realized using full custom IC design, such as cell phones, advanced microprocessors, hearing aids, analog-to-digital converters, temperature sensors, nearly any hand-held electronic device, MEMs and any complete system on a chip which requires both analog and digital functions (e.g. mixed signal).

Semicustom design, on the other hand, allows the designer to work at the logic gate level. Typically there is an array of repeated generic logic elements and the schematic capture or high level description language is then translated to routing paths. This evolved from ROM centered designs. Simple examples of semicustom design are programmable logic arrays (PLA)s. More complex examples of semi-custom design are Field Programmable Gate Arrays FPGAs, such as the XLINX and Altera FPGAs used in some ELE courses, are examples of semicustom design. As much as 60 percent of the logic elements might be unused for a given application. Common applications are controllers, low resolution digital filters and some signal processing applications.

The choice of full custom vs. semi-custom depends upon several factors: economics, time to reach the market and feasibility of each type of implementation fitting within the constraints dictated by the product application.

The advantage of semicustom design are:
1) rapid turn around,
2) design is performed at the logic gate level and
3) simplified verification.

The advantages of full custom design are:
1) substantial reduction in die area,
2) increased control over power consumption and
3) lower cost in high volume.