Basic Definition of Digital Systems

1. Basic Definition of Digital Systems

This article outline the basic definitions of digital systems,  then explain the forms of signals (Analog and Digital), interpretation of logical values ​​in various forms, and also describe their advantages. and lack of digital engineering and examples of digital engineering applications.

Some definitions that are often used in digital engineering :


stands for binary digit , is a unit that shows the amount or data output from a digital system. For examples :
– 4-bit counter, meaning a counter that has 4 outputs.
–  8-bit register is a register consisting of 8 outputs.


is a data line that is 8-bit long.basis


is an electronic system that works on binary digits, is to show the number of numbers in a number system, for example the decimal number system uses 10 digits (0 to 9).


are name, number, and other information needed to solve a problem.


is a display system for a quantity, both analog and digital.


are symbols in the form of images used in the logic circuit.


is an input electronic component or electronic equipment.

A word

is a combination of several bytes


is a series of data that is 4-bit long, often called a half byte.


is the output of electronic components or electronic equipment.


is a set of instructions, which when executed will produce a function.

Logic Circuit

is a series of functions given in the form of logical symbols.

Number System

is a number used for all calculations (binary, octal, decimal, hexadecimal)

True table

a table that shows input and output that apply to a logic circuit.

Analog and Digital Display


Forms of Signal 

Analog Signals 

Analog signal can be in the form of voltage, current or movement of a measuring instrument that shows a value. All of these signals are providing a continuous value.

The relationship between analog voltage vs time


Digital Signal

Digital signal is a discrete signal or not continuous. To explain this, let’s look at how the Digital Clock works, which uses a decimal display to represent the amount of time in hours, minutes, even seconds. As we know that the time of the day is changing continuously, but the digital clock does not read continuously, but on every minute (or per second). In other words the representation of the time of the day changes step by step, compared to an analog clock which shows a continuous change (all values ​​are read) and the values ​​are read via the scale given on the display.


The relationship between digital voltage vs time

The main difference between analog and digital signals can be simply given by the following statement:

Analog = continuous

Digital = discrete (step by step)

Interpretation of Logical Values

In a digital system the information is processed in binary form, while the binary number values ​​in the form of 1 and 0 can be expressed in various forms, as given in Table below.

Representation of binary values 

In digital systems, the voltage values ​​for the two logics are different for each gate family. For the TTL family (Transistor Transistor Logic) the logic “1” is equivalent to (2–5) volts, and for logic “0” it is equivalent to (0–0.8) volts. For a CMOS (complement mos) family, a logic “1” is equivalent to (10–15) Volts, and for a logic “0” it is equivalent to (0–0.1) Volts.

The characteristics of the TTL family are given below :

Arrangement of binary values ​​in terms of voltage

Logic characteristics

VCC Supply voltage

VOH Maximum high output voltage

VOL Maximum low output voltage

VIH Maximum high input voltage

VIL Low input voltage maximum

Advantages and Disadvantages of Digital Engineering


  1. The circuits are easier to design.
  2. The accuracy is higher.
  3. Can be programmed, Analog systems can also be programmed but the variety and complexity
    is limited
  4. Digital circuits are more resistant to interference (noise).
  5. More digital circuits are manufactured in one package (IC chips).
  6. On measuring instruments, it is easier to read (directly in numbers)
  7. In digital systems, the exact value of a voltage magnitude is not important, 3.6V can mean the same as 4.3V for logic 1. In analog systems the quantity is absolute and important.


  1. Economically, digital systems are relatively expensive compared to analog systems
  2. can not be real time in the application.

In its application, to take the advantages of a digital system in an application

with analog input and analog output, three steps are taken, namely:

  1. Convert analog input signal to digital form (ADC)
  2. Process (operation) of information digitally.
  3. Converting back the form of a digital signal to an anolog signal form (DAC)

A block diagram of a temperature control work system that uses an ADC and DAC for the use of digital processing techniques shows below :


Digram of temperature controller block 

Temperature is detected by a sensor (Measuring Device), the results of which are still analog, converted to digital by the ADC. The results of the conversion are then processed digitally. After processing, the signal is returned to Analog form via the DAC. The last result, which is already an analog signal, is then adjusted with the controller as needed.


Digital systems are systems that work with binary numbers, with better quality than analog systems. The application of digital systems in various fields of life is wider than analog systems.