# Digital Electronics

## Digital Electronics

**Digital electronics** is a field of electronics that involves the study of digital signals and electronic circuits that are used to process and control digital signals. By contrast, in analog electronics, where information is represented by a continuously varying voltage, digital signals are represented by two discrete voltages, or logic levels.

## What are logical levels in digital electronics?

In digital circuits and components such as the logic gate, it is common to say that we have a logic “high” or a logic “low” at the input or output of a circuit. If we have a “high” level we say that it is a “1” and if we have a “low” level we say that it is a “0”.

If we were using a TTL IC running on +5 volts, the “1” would be a voltage level of +5 volts and the “0” would be a voltage level of 0 volts. This is the ideal case in digital circuits.

### TTL, CMOS and HC logic levels (voltage levels)

In the real world, these values are different. Digital integrated circuits operate with input and output values that vary depending on the technology of the integrated circuit.

In the TTL family, a logic “0” means the voltage level is between 0 and 0.8 volts and a logic “1” means the voltage level is between 2 and 5 volts.

In CMOS technology, a logic “0” means the voltage level is between 0 and 1.5 volts and a logic “1” means the voltage level is between 3.5 and 5 volts.

## What is a logic circuit in digital electronics?

A logic circuit uses two logic levels to transfer information. A logic high level or “1” and a logic low level or “0”. Logic circuits are made of digital elements such as AND gate, OR gate, NOT gate, and combinations of them.

These combinations give way to other types of digital electronic components, such as logic gates, flip-flops, microprocessors, memories, among others.

Modern **digital electronics** are used to perform many functions. Although digital electronic circuits may seem very complex, they are actually built with many very simple circuits.

## Truth Table

What is a Truth Table?

The Truth Table is used to simplify boolean equations obtained from digital circuits. The truth tables can have many columns, but all tables operate in the same way.

## Logic OR gate

Logic OR gate

The logic Or gate is one of the simplest digital logic gates. The output of this gate is “High”, when one or all of its inputs are “High”. We can also say that, the output of an OR gate is “Low” only when all gate inputs are “Low”.

## NAND Gate – The Universal Gate

NAND gate – Truth table.

NAND gate, also called universal gate, is a gate that produces a logic “0” output only when all logic inputs are “1”. Truth table.

## The logic NOT Gate – Symbol, Truth Table

The logic NOT gate

The NOT gate is a logic gate that has only one input and one output. The output logic level is the opposite of the input logic level

## BCD Code – Binary Coded Decimal

BCD Code – Binary Coded Decimal

In order to share information in digital format, it is common to use a binary or hexadecimal representations (BCD Code). There are other methods to represent this information and one of them is the BCD code.

## Binary Number System – Conversion, Examples

The Binary number system

The Binary Number System, unlike the Decimal Number System, where 10 figures are allowed (from 0 to 9), only needs 2 figures: “0” and “1”.

## NOR Gate – The Universal Gate

NOR gate

NOR Logic gate – Truth Table, equivalent circuit. It can be implemented with the concatenation of an OR gate and a NOT gate.

## Hexadecimal Numbering System – Conversion between numbering systems

The hexadecimal numbering system (base-16)

This numbering system is mainly used to simplify the representation of binary numbers and for the digital handling of colors.

## Digital Logic Levels (hight, low, 1, 0)

Logic Levels (high, low, 0, 1)

In digital circuits is common to say that we have a “high or a “low” logic level at the input or output of a circuit. If we have a “high” level we say it is a “1” and if we have a “low” level we say that it is a “0”.

## Gray code – Gray code Table

The Gray code

The Gray code is a special type of binary code that is unweighted (the digits that make up the code does not have an assigned weight).

## Aiken code – Excess 3 code

Aiken code – Excess 3 code

Aiken BCD code is similar to the natural BCD code, but with “weights” or “values” distributed differently.

The Excess 3 Code is obtained by adding “3” to each combination of the natural BCD code.

## JK Flip-Flop

JK Flip-Flop – PRESET & CLEAR Inputs – Truth Table

The JK Flip-Flop is a sequential device with 3 inputs (J, K, CLK (clock signal)) and 2 outputs (Q and Q’). J and K are control inputs.

## Combinational Circuit

Combinational Circuit Using Logic Gates

A combinational circuit is a circuit where the output depends only on the combination of the inputs at the time we are testing the output

## Sequential Circuit – Digital Logic

What is a sequential circuit? This tutorial explains how a sequential circuit made with gates works. There are other circuits or ICs that already work the sequential way, like a flip-flop. For…

## Logic AND Gate – AND Truth Table

What is a Logic AND gate?

The logic AND gate is one of the simplest gates in Digital Electronics. The output of an AND gate is true (“1”) only when all inputs are true (“1”). If one or more inputs are false (“0”), then the output is false (“0”).

## OR and AND logic gates made with diodes

OR and AND logic gates made with diodes

Diode Logic OR gate (wired OR connection) and Diode Logic AND gate (wired AND connection). Diode Logic uses the fact that diodes conduct only in one direction. (they behave like switches)

## XOR Logic Gate

XOR logic gate

In digital electronics there are special gates. One of them is the XOR logic gate or exclusive OR gate. Equivalent XOR Logic Gate using common logic gates

## NAND gate using transistors

NAND gate using transistors

This NAND gate using transistors circuit simulates the operation of a two or more inputs NAND gate. (There is a diode for each input. D1, D2, …)

## Binary to Gray code and Gray code to Binary Conversion

Binary to Gray Code Conversion and Gray code to Binary Conversion.

Two Methods. One method to convert from binary to gray code and another to convert from gray to binary code

## Boolean Algebra – Introduction and Rules

Boolean Algebra – Introduction and Rules.

Boolean Algebra is a tool to reduce logical expressions. It is the mathematics of logical expressions, which was presented by George Boole in 1854.

## What is a Binary Decoder?

What is a Binary Decoder?

The binary decoder is a device that accepts a digital input (in binary form) and it activates one of its outputs. This device has several outputs, and the one that is activated is chosen by the code applied to the inputs.

## What is a Logic Circuit?

What is a logic Circuit?

A Logic circuit uses two logic levels to transfer the information. A hight logic level or “1” and a low logic level or “0”. The Logic circuits are made of digital elements such as the AND gate, the OR gate, the NOT gate and a combinations of them.