1 INTRODUCTION

Two special logic gates that are of fundamental importance and are used more often in digital systems are the Exclusive-OR (XOR) and Exclusive-NOR (XNOR) circuits. XOR and XNOR gates are formed by a combination of AND-OR-INVERT (AOI) logic. This application demonstrates the use of logic gates that simulates a 2-way switch like the ones in our homes to turn a staircase light ON/ OFF from switches located on two different floors.

1.1 XOR GATE

1.2 APPLICATION: STAIRCASE- LIGHT CONTROL

A two-way switch can be simulated by making use of either AOI logic or using XOR logic. A two -input XOR gate produces a HIGH output whenever the inputs are at opposite levels. This concept of XOR functionality makes it applicable at home/offices to control passage lights, fans, night lamps, staircase lights etc.

1.3 CONCEPT: A floor lamp in a staircase has two switches, one switch being at the ground floor (switch A) and the other one on the first floor (switch B). The bulb can be turned ON/OFF by any one of the switches irrespective of the state of the other switch. The logic of switching of the lamp resembles an XOR gate whose Boolean expression is Y = A'. B + A.B' (Read as: A bar B + A B bar).

Comparison between two approaches can be understood in this experiment:

1. AOI LOGIC BASED STAIRCASE-LIGHT CONTROL

2. XOR gate Based Staircase-Light Control

AOI approach leads to three-level logic, whereas XOR logic leads to single-level logic. Let the propagation delay of each gate be say τ. Then AOI based design needs about 3τ and XOR design needs just τ amount of time to produce the result.