TABLE OF CONTENTS The performance of a CMOS VLSI chip is measured by its integration density, switching speed, and power dissipation. CMOS circuits have the unique characteristic of practically zero standby power, which enables higher integration levels and makes them the technology of choice for most VLSI applications. This chapter examines the various factors that determine the switching speed of basic CMOS circuit elements.
In a modern CMOS VLSI chip, the most important function components are CMOS static gates. In gate array circuits, CMOS static gates are used almost exclusively. In microprocessors and supporting circuits of memory chips, most of the control interface logic is implemented using CMOS static gates. Static logic gates are the most widely used CMOS circuit because of their simplicity and noise immunity. This section describes basic static CMOS circuit elements and their switching characteristics.
Circuit symbols for nMOSFETs and pMOSFETs are defined in Fig. 5.1. A MOSFET is a four-terminal device, although usually only three are shown. Unless specified, the body (p-substrate) terminal of an nMOSFET is connected to the ground (lowest voltage), while the body terminal (n-well) of a pMOSFET is connected to the power supply V dd (highest voltage).
The most basic element of digital static CMOS circuits is a CMOS inverter. A CMOS inverter is a combination of an nMOSFET and a pMOSFET, as shown in Fig. 5.2 (Burns, 1964). The source terminal...
