# Digital Electronics

**Digital electronics** or **digital (electronic) circuits** are electronics that handle digital signals (discrete bands of analog levels). All levels within a band of values represent the same information state. In most cases, the number of these states is **two**, and they are represented by two voltage bands. These correspond to the **false** and **true** values respectively of the Boolean domain.

In contrast, **analog circuits** operate on analog signals whose performance is more subject to manufacturing tolerance, signal attenuation and noise. **Digital techniques are useful** because it is easier to get an electronic device to switch into one of a number of known states than to accurately reproduce a continuous range of values.

Digital electronic circuits are usually made from **large assemblies of** logic gates (often printed on integrated circuits), simple electronic representations of Boolean logic functions.

## Overview

**Digital Electronics**

Abbreviation | DE | ||||||
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Course | SE | ||||||

Credits | |||||||

Examination Scheme
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Language | English |

## Table of Contents

## Course Objectives

The concept and theory of digital Electronics are needed in almost all electronics and telecommunication engineering fields and in many other engineering and scientific disciplines as well. The main objective of this course is to lay the foundation for further studies in areas such as communication, VLSI, computer, microprocessor etc. One of the most important reasons for the unprecedented growth of digital electronics is the advent of integrated circuit. This course will explore the basic concepts of digital electronics.

## Course Outcomes

Having successfully completed this course, the student will be able to:

- Understand the basic logic gates and various variable reduction techniques of digital logic circuit in detail.
- Understand, identify and design combinational and sequential circuits
- Design and implement hardware circuit to test performance and application for what it is being designed.
- Simulate and verify using computer simulation software to obtain desired result.
- Understand and verify simulated circuit model with hardware implementation.

## Syllabus and Notes

### Unit 1: Combinational Logic Design

Main Page: *Combinational Logic Design*

- Standard representations for logic functions, k map representation of logic functions (SOP and POS forms), minimization of logical functions for min-terms and max-terms (upto 4 variables), don’t care conditions, Design Examples: Arithmetic Circuits, BCD - to – 7 segment decoder, Code converters. Adders and their use as subtractor, look ahead carry, ALU, Digital Comparator, Parity generators/checkers, Multiplexers and their use in combinational logic designs, multiplexer trees, De-multiplexers and their use in combinational logic designs, Decoders, demultiplexer trees. Introduction to QuineMcCluskey method.

### Unit 2: Sequential Logic Design

Main Page: *Sequential Logic Design*

- 1 Bit Memory Cell, Clocked SR, JK, MS J-K flip flop, D and T flip-flops. Use of preset and clear terminals, Excitation Table for flip flops. Conversion of flip flops. Application of Flip flops: Registers, Shift registers, Counters (ring counters, twisted ring counters), Sequence Generators, ripple counters, up/down counters, synchronous counters, lock out, Clock Skew, Clock jitter. Effect on synchronous designs.

### Unit 3: State Machines

Main Page: *State Machines*

- Basic design steps- State diagram, State table, State reduction, State assignment, Mealy and Moore machines representation, Implementation, finite state machine implementation, Sequencedetector. Introduction to Algorithmic state machines- construction of ASM chart and realization forsequential circuits

### Unit 4: Digital Logic Families

Main Page: *Digital Logic Families*

- Classification of logic families, Characteristics of digital ICs-Speed of operation, power dissipation, figure of merit, fan in, fan out, current and voltage parameters, noise immunity, operating temperatures and power supply requirements.TTL logic. Operation of TTL NAND gate, active pull up, wired AND, open collector output, unconnected inputs. Tri-State logic. CMOS logic – CMOS inverter, NAND, NOR gates, unconnected inputs, wired logic , open drain output. Interfacing CMOS and TTL. Comparison table of Characteristics of TTL, CMOS, ECL, RTL, I2L, DCTL.

### Unit 5: Programmable Logic Devices and Semiconductor Memories

Main Page: *Programmable Logic Devices and Semiconductor Memories*

- Programmable logic devices: Detail architecture, Study of PROM, PAL, PLA, Designing combinational circuits using PLDs.
- General Architecture of FPGA and CPLD (Complex Programmable Logic Devices)
- Semiconductor memories: memory organization and operation, Classification and characteristics of memories, RAM, ROM, EPROM, EEPROM, NVRAM,
- Expanding memory size,
- SRAM,DRAM.

### Unit 6: Introduction to Microcontroller 8051

Main Page: *Introduction to Microcontroller 8051*

- Microprocessors and Microcontrollers comparison, 8051 architecture, Pin description, Addressing modes, Instruction set of 8051, Concepts of Counters and Timers with the help of status registers, Port Structure and Interrupts. Simple programming examples – for addition, subtraction, multiplication and delay.

## LAB Experiments

**List of Experiments**:

All the following Practicals are mandatory.

- Study of IC-74LS153 as a Multiplexer. (Refer Data-Sheet). Design and Implement 8:1 MUX using IC-74LS153 & Verify its Truth Table. Design & Implement the given 4 variable function using IC74LS153. Verify its Truth- Table.
- Study of IC-74LS138 as a Demultiplexer / Decoder (Refer Data-Sheet). Practical) (Test Benches and FSM excluded). Design and Implement full adder and subtractor function using IC- 74LS138. Design & Implement 3-bit code converter using IC-74LS138.(Gray to Binary/Binary to Gray)
- Study of IC-74LS83 as a BCD adder,(Refer Data-Sheet). Design and Implement 1 digit BCD adder using IC-74LS83 Design and Implement 4-bit Binary sub tractor using IC-74LS83.
- Study of IC-74LS85 as a magnitude comparator,(Refer Data-Sheet) Design and Implement 4-bit Comparator. Design and Implement 8-bit Comparator
- Study of Counter ICs (74LS90/74LS93). (Refer Data-Sheet) Design and Implement MOD-N and MOD-NN using IC-74LS90 and draw Timing diagram. Design and Implement MOD-N and MOD-NN using IC-74LS93 and draw Timing diagram.
- Study of synchronous counter Design & Implement 4-bit Up/down Counter and MOD-N Up/down Counter using IC74HC191/ IC74HC193. Draw Timing Diagram
- Verify four voltage and current parameters for TTL and CMOS (IC 74LSXX, 74HCXX), (Refer Data-Sheet).
- Study of Shift Register (74HC194/74LS95), (Refer data-Sheet) Design and Implement Pulse train generator using IC-74HC194/IC74LS95 (Use right shift/left shift). Design and Implement 4-bit Ring Counter/ Twisted ring Counter using shift registers IC 74HC194/IC74LS95.
- Write a assembly/C language program to perform arithmetic operations.
- Write a assembly/C language program to perform internal and external memory transfer operations
- Write a assembly/C language program to use port pin for simple application

## Previous Years Questions

## Practical/ Oral Exam Questions

## Multiple Choice Questions

Unit 1 | Unit 2 |

Unit 3 | Unit 4 |

## Assignments

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## References

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