Introduction to Digital Logic Design

What is Digital Logic Design?

At some point in our education or even our daily lives, we have all heard the terms “analog devices” and “digital devices”. Where analog devices use analog signals, digital devices use digital logic design to enter, interpret, and display data. In a digital system, values are discrete and there are only two states- it is either 1 or 0, or it is either ‘on’ or ‘off’. This digital, binary representation of input and output data is basically what digital logic design is.

How Does Digital Logic Design Work?

A typical digital logic design comprises various logic gates that constitute the digital device. The logic gates are printed onto the integrated circuits which make up the overall electronic circuit of a particular digital device. To understand these digital logic better, we can interpret and represent these values using Boolean logic functions.

Understandably, digital logic design forms the very basis of everything that electronic systems and electrical or computer engineering stands for. Digital logic allows these engineers to play around with various functions and build complex circuits with particular characteristics that execute a specific function. It uses binary code, a host of 1s and 0s in specific conventions and orientations to represent opposite values. These binary inputs and outputs are manipulated by logic gates having certain functions, such as AND, OR, and NOT gates.

A digital design engineer has knowledge regarding these functions and their properties as well as about the various programming languages such as Hardware Descriptive Language (HDL) that helps them program and develop circuit boards and microchips.

What Are Digital Logic Gates?

Logic gates can be defined as the building or foundation blocks that constitute a larger logic design and circuit. These gates take the combination of digital signals received on its input pins and process them to make logical decisions. Logic gates are made using transistors, resistors, and diodes, with different kinds of gates requiring a different number of transistors.

It is not necessary for a single gate to be used in a single circuit- multiple logic gates can be used in a connected or cascading manner to build combinational or sequential circuits that have a combined logic function which is different than that of the basic logic gates. When it comes to types of logic gates, you first have the basic ones (AND, OR, NOT) and then you have the additional ones that are useful in certain applications (NAND, NOR, XOR).

As we previously discussed, digital logic design uses a binary system where two states are possible- either Logic 1 (high/true/on) or Logic 0 (low/false/off). For each of the individual logic gates, you can create a truth table using Boolean algebra representatives in the form of 1 and 0. This is typical of a Positive Logic system. You will also find some Negative Logic systems that have opposite values for 1 and 0. These values and their interaction is specified in a lookup table which can be programmed and reprogrammed as needed without ever having to modify the hardware of the device.

Logic Gates and Their Truth Table

Here, A and B represent the two inputs that are entering the circuit, whereas F represents the output. A truth table shows all the possible input combinations and the definite result of each of them.

Application of Digital Logic Design

As mentioned before, electrical and computer engineering is often based on digital logic design. They use the specific characteristic of these logic functions to build complex circuits for electronic components. The end result of the logic design and implementation process are circuit boards and chips (i.e. microchip processors) housing the logic gates and functions. Each component has a unique set of characteristics defined by the logic, such as power, input, protocol, and logic function.

Digital circuits are typically preferred over analog circuits because there is no signal degradation due to noise that is usually produced in the latter. The discrete binary values can be picked up in the transmission through the noise and reconstructed without any flaws. Digital devices that use digital logic design are implemented across a variety of fields and applications. You will find them being used in medical and aviation equipment, in military navigation systems, as well as in everyday consumer products such as your humble smartphone.