Electronics - SS2 Physics Past Questions and Answers - page 5

A 4-input NAND gate is a logic gate that produces an output of logic level 0 (LOW) only when all of its inputs are at logic level 1 (HIGH). The truth table for a 4-input NAND gate is as follows:

 

 

One practical application of a 4-input NAND gate is in digital circuits where the output should be HIGH only when multiple conditions are met simultaneously. For example, in a security system, if multiple sensors need to be triggered for an alarm to activate, a 4-input NAND gate can be used to combine the sensor outputs. The alarm will sound only when all the sensors detect an intrusion.

A 2-input XOR gate is a logic gate that produces an output of logic level 1 (HIGH) when the number of inputs at logic level 1 is odd. The truth table for a 2-input XOR gate is as follows:

 

 

XOR gates are significant in digital logic circuits because they are used for several purposes. Firstly, XOR gates are fundamental building blocks for constructing other types of gates, such as XNOR gates and half-adders. Secondly, XOR gates are widely used in error detection and correction circuits, such as parity checkers. Additionally, XOR gates are employed in data encryption and decryption algorithms, where they play a crucial role in the generation of cryptographic keys.

A multiplexer, or MUX, is a digital device that allows multiple inputs to be selectively routed to a single output based on control signals. It is often referred to as a data selector. A multiplexer consists of two main components: the data inputs and the control inputs. The control inputs determine which data input is passed through to the output.

The operation of a multiplexer can be explained using a 4-to-1 MUX as an example. A 4-to-1 MUX has four data inputs, one output, and two control inputs. The control inputs, typically denoted as S0 and S1, select one of the four data inputs to be routed to the output. The selection is based on the binary value of the control inputs.

A practical application of a multiplexer is in digital communication systems. For example, in a telephone system, a multiplexer is used to combine multiple voice signals from different callers into a single transmission line, allowing efficient use of the available bandwidth. The control inputs of the multiplexer determine the caller whose voice signal is being transmitted