A signal is a time-varying entity that carries some information from source to destination. Signals can be of many types such as electrical signal, sound signal, light signal, etc. In electronics, communication, and electrical engineering, we care about the electrical signals the most. For transmission of any other signals, we first need to convert them into electrical signals using some kind of transducer. Signals can be classified into the following categories:
- Continuous-Time and Discrete-Time Signal
- Analog and Digital Signal
- Energy and Power Signal
- Periodic and Non-periodic Signal
- Even and Odd Signal
- Deterministic and Random Signal
Analog and Digital are two of the most used terms in communication. Analog signal and digital signal, both are used in the modern communication system. In this article, we are going to learn the actual difference between analog and digital signal.
Difference Between Analog and Digital Signal in tabular form
In the following table, we are going to discuss the differences between analog and digital signals.
| Analog Signal | Digital Signal |
| Analog signal amplitude can have any real and possible value. | Digital signal amplitude can have only a finite number of values. |
| Analog signals are more common in nature. | Digital signals are less common in nature. |
| Analog signal has a continuous amplitude over time. | Digital signal amplitude has discrete levels. |
| Analog signals require smaller bandwidth for transmission than digital signals. | Digital signals require larger bandwidth for transmission than analog signals. |
| Analog signals are less immune to noise i.e., the effect of noise is harder to remove in the case of analog signals. | Digital signals are more immune to noise. |
| As most of the natural signals are analog signals, the chances of data loss are low (if we use sophisticated devices) | As digital signals are created from analog signals by sampling and quantization, the signal gets distorted and thus loss of data happens. |
| Generation and transmission of analog signals are less costly as they are more common in nature and easy to generate. | As digital signals are not commonly found in nature and are generated from analog signals using ADC, the cost of generation and transmission of digital signals is greater than analog signals. |
| Regeneration of analog signals is very difficult as their amplitude has a continuous value. And during recovery or regeneration, the shape of the analog signal must be preserved. | Regeneration or recovery of digital signals is easier as its amplitude has a discrete and finite number of values. |
| Example – Voice, sounds, temperature, etc. | Example – Morse code |
What is Analog Signal?
We have already discussed that signal is a time-varying entity. An Analog signal is a signal whose amplitude can have any real possible value and is continuous over time. Analog signals are more common in nature; voice and sound signals, light signals, temperature are actually analog signals.
An analog signal can be defined using its four properties that are – amplitude, frequency, phase, and polarization. As the amplitude of the analog signal is continuous over time and can have any real values, the shape of the analog signal curve (amplitude vs time plot) must be preserved to recover the information.
Advantages of Analog signals
1. It is easier to generate and process an analog signal
2. Circuitries involving analog signals are low-cost and simple.
3. It uses smaller bandwidth in communication
Disadvantages of Analog signals
1. Analog signals are less immune to noise.
2. Recovering or regenerating analog signals is difficult as the shape of the signal is very important in this case.
3. It is difficult to edit and encrypt analog signals.
What is Digital Signal?
A digital signal is a signal whose amplitude can have a finite number of discrete values. A binary signal is an example of a digital signal. “Bi” means two. The amplitude of a binary signal can have only two values – logic-0 or LOW and logic-1 or HIGH. This is why the signal is called binary signal. A digital signal whose amplitude can have M number of discrete values is called an M-ary signal.
Digital signals are not very common in nature. We need to convert analog signals into digital signals using ADC or Analog to Digital Converter that includes sampler, quantizer, etc. We use digital signals as it provides many advantages in communication.
Advantages of Digital Signal
1. Digital signal is more immune to noise.
2. We can perform encryption on digital signals using specific techniques.
3. It is easy to regenerate or recover as the amplitude levels are finite.
Disadvantages of Digital Signals
1. Sampling and quantizing results in loss of information.
2. Requires complicated and costly hardware.
3. Digital signal requires larger bandwidth for transmission.
Conclusion
Both Analog and digital signals have their advantages and disadvantages. Using analog signals in an electronic circuit, the signal amplitude gets distorted or discretized, due to some effects and limitations. In the case of digital signals, as well, we face such issues. Though the levels are discrete, the conjunction of two consecutive levels tends to be continuous due to some limitations. So, we don’t get ideal analog or digital signals as the outputs. The use of sophisticated devices reduces the error we get at the output signal of each type.
Author
Subhrajyoti Choudhury
University of Calcutta, Kolkata
