Digital Electronics

# Digital and Analogue Quantities and Comparison of Merits & Demerits

## Digital and Analogue Quantities

Digital and Analogue Quantities and Comparison of Merits & Demerits- An analogue quantity is one that contains continuous values, whereas conversely, digital quantities always consist of a discrete set of different values. Most of the items existing in the universe, which can be measured, are represented in an analogue form. For example, temperature, time, pressure, distance, sound, etc. Take the example of air temperature, it does not move on from 70°C to 71°C at once. It, in fact, has to cover all the extreme values existing between 70°C and 71°C, and only then can it reach 71°C. That’s to say air temperature changes quite gradually after crossing a continuous range of values.

Any quantity which changes with respect to time can be demonstrated through an analogue signal or it can also be used as a digital signal. For instance, if some water pot is provided heat by putting it on a stove at room temperature, in such a situation the desired quantity can be measured through changes in water temperature. There are normally two methods being used for recording changes in water temperature during a specific period of time i.e. analogue and digital, as has been shown in figure 1.2

In figure (a), the temperature has been recorded continuously and this temperature tends to change quite smoothly from 20°C to 80°C. As a result of heating water, its temperature reaches 80°C after crossing all the possible values within the range of 20°C to 80°C. This is an example of analogue signal. Keep in mind that analogue signals are continuous and they tend to reflect the whole range of possible values.

If the water temperature is measured just once in a minute and if changes in the values of water temperature are recorded after every passing minute, as has been depicted in the figure, in such a situation, the recorded temperature does not keep in a continuous state, rather it keeps jumping from one point to the other. Thus, a number of finite values are accrued between 20°C to 80°C (in this situation, 11 values are received, as can be seen in the figure). When a quantity is recorded in the form of continuous-discrete points, it is called a sample. It is an example of digital signals. A Digital signal denotes a finite number of individual or discrete values.

Figure 1.2 (a) An analogue continuous signal (b) A digital (discrete) signal

Whether a light-providing bulb is analogue type or digital, depends on its usage. For example, value of current passing through the bulb can be changed via setting the current value on any value below its rated value. Thus, the intensity of light changes with the changes in current. As bulb light is directly proportionate to the current flowing through it (i.e. light increases due to an increase in current and light diminishes with a decrease in current, thus different light levels can be obtained by means of fluctuating current through a potentiometer or a variable resistance. Such typical application of a bulb suggests towards the fact that the bulb is of analogue type. If the current passing through the bulb and its light/radiation is converted into discrete steps, (that’s if just two levels are given to it through a switch, ON or OFF), the bulb becomes a digital device, because two states of the bulb (ON/OFF) represents its binary condition (i.e. the bulb will either turn ON or it will turn OFF). In figure 1.1, an analogue and a digital signal have been illustrated. From figure (a), it is evident that an analogue signal change continuously but slowly. Whereas digital signal has got just two levels that’s low or high and 0 or 1 (as can be seen in figure b). In other words, digital signal operates in discrete steps and changes its status abruptly, getting either high or low.

As VHF channel selector Switch present on a TV set adopts different discrete positions (that’s it can be set on any one of the different given states/ conditions), therefore this switch may also be given as an example of the digital device. On the contrary, volume control of a TV set is an analogue device or switch, because it has to be changed from an OFF condition up to a wide range continuously.

A Speedo meter fitted in a car continuously monitors variations in a car’s speed per hour, because when car is driven, its speed varies with respect to time. Therefore, it is an analog device. However, the odometer fixed in the speedo meter represents car mileage in kilo meters (that’s it changes its condition by one step after every covered kilo meter and thus shows the overall covered distance in kilo meters). As such, it is a digital device.

Such measurement instruments which indicate their measured values with the help of a calibrated scale by means of a needle or pointer, e.g. volt meter, ampere meter, frequency meter and ohm meter etc.) are analogue measurement instruments, because their pointers tend to move continuously alongside changes in the amplitude values. Inversely, measurement instruments which do not have any pointer or scale and display their measured values in the form of discrete digits, are called digital instruments.

Needle clocks or wrist watches are also an example of analogue devices, because they indicate time continuously by means of its hands on the dial. However, it is necessary to ascertain the exact position of hourly, minutes, and sometimes even seconds hand in order to determine time accurately. However, no such hardship is confronted while measuring time through digital type of watches or clocks, because it can display time (hours, minutes and seconds) directly in digits form, which results in displaying the actual and accurate time immediately.

## Comparison of Merits & Demerits of Digital and Analogue Quantities

The comparison of merits and demerits of analogue and digital quantities (besides analogue and digital circuits and devices) is as follows:

 Digital Quantity Analogue Quantity 1. Digital data can be processed and transmitted with a relatively better efficiency 1. Analogue data can be processed or transmitted with a relatively less efficiency 2. It is more reliable as compared to an analogue 2. It is less reliable quantity as compared to digital 3. Its quantity can be stored quite easily and requires little space. It can be reproduced more efficiently and with greater accuracy as compared to analogue. 3. It is relatively hard to store this quantity or restore it accurately to its earlier position 4. It is non-linear quantity 4. It is a linear quantity 5. Digital circuits are mostly used on large signals 5. Anal circuits are used with small   signals 6. Digital circuits, using the digital quantities are small in size and relatively less heavy 6. Analogue circuits using analogue quantity are comparatively large in size and relatively heavy 7. Comparatively power efficient 7. Consume more power 8. Less costly 8. Are relatively costly 9. Measurement obtained through devices with digital quantities are more accurate 9. The measurement of different quantities through the application of analogue quantity does not prove so correct 10. It is more popular due to a higher signal to noise ratio 10. Its signal to noise ratio is low 11. Digital devices are also equally affected by climate factors 11. Analogue instruments and circuits are relatively less affected by climate factors (e.g. temperature and moisture) 12. it has the facility of being fully automated 12. It is difficult to perform various kind of tasks e.g. different processes, control, data recording, supervision or monitoring etc. under an automatic system 13. Its designing is quite easy and requires comparatively less time to fabricate a particular product 13. Analogue devices require lot of time from designing to the manufacturing of the product 14. It requires low voltages for its operation 14. It requires higher voltages for its operation 15. The data has to be changed frequently due to being incompatible with the real world, therefore it is difficult for a lay man to comprehend and use it 15. As this quantity conforms to the real world, therefore its usage is quite convenient

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