Chapter 1 : Introductory Concepts

1.1 Numerical representations

1.2 Advantages of Digital systems

1.3 Limitations of Digital systems

CHAPTER 1: Introductory concept 1.1 Numerical Representations In science & technology, we are constantly dealing with quantities. There are two ways of

representing the numerical value of quantities: - Analog - Digital

Analog representation Digital representation

• a quantity is represented by a voltage, current or meter movement that is proportional to the value of that quantity.

•it is continuous wave form that changes smoothly over time.

•example1 : An automobile speedometer, in which the deflection of the needle represents the value of the automobile speed.

• the quantities are represented by symbols called digits.

•it is discontinuous signal expressed as a burst of ON and OFF electrical pulse.

•Digital quantities vary in discrete values.

•Example : Digital watch, computer system.

Major difference between analog and digital quantities :

analog = Continuous

digital : Discrete (step by step)

0

2

4

¼ ¾

-2

-4

wt

v(t)

0 1 0 0 1 00

5

V

time

LOW (0) or FALSE : 0 Volt

HIGH (1) or TRUE : 5 Volts

1.2 Advantages of Digital Techniques Digital systems are generally easier to design.

Digital instruments and equipment are easier to use, because the direct display of data is convenient to read. Eg: a digital multi-meter.

Because digital systems use switching circuits, where exact values of voltage and current are not important, only the range (HIGH or LOW) in which they fall.

Information storage and retrieved functions are much easier to implement because digital equipment has the ability to receive, hold, and retrieve information.

Accuracy and precision are greater

Digital systems can handle as many as digits of precision as you need simply by adding more switching circuits. ( in analog systems, precision is usually limited to three or four digits because the values of voltage and current are directly dependent on the circuit components values)

Operation can be programmed.

Ease to design digital systems whose operation is controlled by a set of stored instructions / algorithm called a program.

Digital circuits are less affected by noise.

Digital circuits are less affected by noise and interference.

Fewer transmission problems. (digital systems transmit data in term of ‘1’ and ‘0’)

More digital circuitry can be fabricated on IC Chips

Less complexity compared to analog.

1.3 Limitation of Digital Techniques The real world is analog in nature.

The quantities that are being monitored and controlled by a system are analog in nature. These quantities such as temperature, pressure, position, velocity, liquid level, flow rate, and so on. If we really want to represent these quantities digitally, or we are about to take advantage of digital techniques when dealing with analog inputs and outputs, three steps must be taken:

Step 1: Convert the analog inputs to digital form. We say ‘analog-to-digital conversion (ADC)’.

Step 2: Process the digital information.

Step 3: Convert the digital output back to analog form. We say ‘digital-to-analog conversion (DAC)’.

Example of temperature control system

(analog) (digital) (digital) Temperature

(analog)

(analog)

Adjusts

Temperature

Description:

•The analog temperature is measured and the measured value is then converted to a digital form by an analog-to-digital converter (ADC).

•The digital quantity is then processed by the digital circuitry.

•Its digital output is converted back to an analog quantity by a digital-to-analog converter (DAC).

•This analog output is fed to a controller which takes some kind of action to adjust the temperature.

End of Chapter 1