Digital Integrated Circuit Design
Working from the fundamentals of transistor-level design and building up to system-level considerations, this text demonstrates how to design state-of-the-art high performance digital integrated circuits.
TABLE OF CONTENTS Digital Integrated Circuit Design
Chapter 5: Transmission-Gate and Fully Differential CMOS Logic
This chapter describes two alternative design methodologies for CMOS gates. The first of these uses transmission gates to minimize the number of transistors required. Transmission gates are very simple switches composed of one or two transistors. They function very much like relays, which were perhaps the first components ever used to realize electronic digital circuits. Many logic circuits, such as adders and D flip-flops, are often realized using transmission gates.
The second logic family introduced in this chapter, and covered in more detail in Chapter 9, is fully differential logic design. This family uses two wires to represent every digital signal; the voltage difference between the lines determines the logic value. This design family is rapidly gaining in popularity and therefore might often be described at an introductory level in a first-level course.
5.1 Transmission-Gate Logic Design
Until now, we have seen only traditional techniques for MOS logic circuit design. An alternative technique often used, particularly for multiplexors and circuits that require exclusive-or functions, makes use of transmission gates. A transmission gate operates much like a voltage-controlled switch or a relay. The simplest example consists of a single n-channel transistor as is shown in Fig. 5.1a. This type of transmission gate, which is often called a pass transistor, was used extensively in NMOS design. It is also often used in CMOS design, except for p-well processes. [1] For p-well processes, the body effect is quite large and, as we shall...
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