Most of the people are familiar with ordinary electrical circuits where voltages and currents can be measured with dial-type meters or analog meters as they are technically called. Such meters follow changes in voltage (or current) in a smooth step-less manner. This is what analog really means in electronics: signals or physical quantities which can vary in smooth-changing, a step-less manner.
An analog quantity is represented as a continuous range of values between two expected extremes. For example, voltage across a certain component in an electronic circuit may be measured as 4.5V or 4.49V or 4.487V or 4.4869V, depending upon the accuracy of measuring instrument.
The above Fig. represents an analog signal. It is also sometimes called continuous signal as value of the quantity is continuous and could have any of the infinite theoretically possible values between the two extremes.
ANALOG VS DIGITAL
Unlike analog circuits in which the signal amplitudes can assume any value, the digital circuits are those in which signal amplitudes are restricted to assume only two values: HIGH (H) or LOW (L). The High and Low voltage levels are denoted by V (1) or VHand V(o) or VL respectively. The two levels, or states of a signal variable can be considered to be representing the two numerals 1and 0 of the binary number system or the two logic states viz. TRUE and FALSE in logic operations. Besides computers, many devices such as mobile phones, TV and various other consumer products are digital. We shall now discuss the advantages of digital circuits over analog circuits.
1. Digital signals can be transmitted without degradation. They are more reliable than analog signals which are subject to degradation due to noise. In case of highly sensitive operations, analog signals can produce wrong results.
2. Digital communication is generally error free so many successive copies can be made indefinitely. Making successive copies of an analog communication is infeasible because each generation increases the noise (disturbance).
3. Information storage can be easier in digital systems than in analog ones. The noise immunity of digital systems permits data to be stored and retrieved without degradation.
4. Digital systems are much easier to design than analog circuits. An analog circuit is manually designed and process is less automated than for digital systems.
5. More digital circuitry can be fabricated on Ie chips because of their small size. So far we have discussed the advantages of digital systems. But we cannot ignore analog systems also. Following are the reasons that tell us why analog circuits are also important.
(a) While transmitting data between very distant locations, analog transmission is much cheaper and easier. It is very easy to amplify the analog signals as compared to digital signals.
(b) Digital circuits use more energy than analog circuits to accomplish the same tasks, thus producing more heat.
(c) In some systems, if a piece of digital data is lost or misinterpreted, the meaning of large blocks of related data can completely change. As a result, it is difficult for users to tell whether a particular system is right or on the edge of failure.
Most of the commonly used signals such as sound, temperature, pressure etc. are all analog one, so there is always a need for a device which can interpret analog signals.
From our discussion, we conclude that both digital and analog circuits are important.