Digital VLSI Design and Simulation with Verilog

1 Combinational Circuit Design

This chapter describes the combinational logic circuits design and their implementation with logic gates, multiplexers, decoders, etc. Combinational circuits are the major block of any digital design or function [1]. So, a detailed overview before the design and analysis of digital circuit with Verilog modules, plays a significant role in hardware optimization to achieve the desired outcomes.

1.1 Logic Gates

Logic gates are very useful when performing a few basic operations in any digital computer system. These logic gates perform many operations in complex circuits and other control systems, e.g., basic operations like AND, OR, and NOT. The functionality of each basic gate as well as the extended version are discussed in this chapter.

AND operation:

It performs the AND operation. The circuit diagram of the N input AND operation is shown in Figure 1.1.

Figure 1.1 Symbol of an AND gate.

The AND gate may have N number of inputs and one output. If the number of inputs are N then N ≥ 2 conditions must be applied for input operation. Digital inputs are applied in terms of A, B, C……N, and the output is Y.

The mathematic equation is given below:

The truth table for an AND gate is provided in Table 1.1

Table 1.1 T. Table of AND gate.

I/P	O/P
A