Question

Differentiate analog signal and digital signal with diagrams.

Answer 1

The message signals can be of two types:
(i) Analog signal and (ii) digital signal. These two types of signals can be differentiated on the following basis.
(i) Analog signal:

A signal in which the current or voltage value varies continuously with time, is called the analog signal.
The most simplest form of analog signal is the sinusoidal signal which can be represented as follows:
$E=E_0\sin \omega t$
Here $E_0$ is the peak value (or amplitude) or voltage, $\omega$ is the angular frequency and $E$ is the instantaneous value of voltage. The angle $\omega t$ is called the phase of voltage. If $T$ is the time period, then $\omega =\frac{2\pi }{T}$
Figure shows a sinusoidal analog signal $E=E_0\sin \omega t$. It is clear that the maximum value of voltage is $+E_0$ and minimum value of voltage is $-E_0$.
To express the value of analog signal, we make use of decimal number system at the base of $10$.
For example, the signal obtained from the sounds of speech, music, vibrating tuning fork etc., are the analog signals which are obtained by microphone as voltage or current signal varying with time. Generally the frequency range of analog signals for audible sound is from $20Hz$ to $20KHz$.

(ii) Digital signal:

A signal which is in form of pulses, i.e., in which there is voltage or current only for some discrete values of time and it is rest for rest of the time, is called a digital signal.
A digital signal is thus a discontinuous function of time. It has only two levels which are expressed as $0$, $1$ or OFF, ON, or LOW, HIGH, or OPEN, CLOSED etc. Here $0$ (zero) and $1$ (one) are called bits.
A digital signal is expressed by the binary number system at the base of $2$.
For example the letters of a book, the list of data, output of a digital computer, fax etc., are the digital information. They are communicated only by digital signals.