1. ANALOG
AND
D I G I TA L
SIGNALS
By :
SANA ULLAH

2. ANALOG SIGNALS
• PCs often communicate via modems over telephone lines using
analog signals which are formed by continuously varying voltage
levels:
• Analog data are continuous and take continuous values.
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ANALOG & DIGITAL SIGNALS

3. ANALOG SIGNALS
How signals travel?
• There are three types of transmission media, each with many
variations:
• conductive metal, like copper or iron, that carries both digital
and analog signals; coaxial cable and twisted wire pairs are
examples,
• transparent glass strand or optical bre that transmits data using
light waves,
• no physical connection that transmits data using
electromagnetic waves (as those used in TV or radio
broadcast).
• The three main characteristics of analogue signals are, 3
ANALOG & DIGITAL SIGNALS

4. 1.AMPLITUDE
• This is the strength of the signal.
• It can be expressed a number of different ways (as volts, decibels).
• The higher the amplitude, the stronger (louder) the signal.
The decibel is a popular measure of signal strength.
Sound level Type of Sound
40db normal speech
90db lawn mowers
110db shotgun blast
120db jet engine taking off
120db+ rock concerts 4
ANALOG & DIGITAL SIGNALS

5. • 2.FREQUENCY
• This is the rate of change the signal undergoes every second,
expressed in Hertz (Hz), or cycles per second.
• A 30Hz signal changes thirty times a second.
• In speech, we also refer to it as the number of vibrations per second.
• As we speak, the air is forced out of our mouths, being vibrated by
our voice box.
• Men, on average, tend to vibrate the air at a lower rate than women,
thus tend to have deeper voices.
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ANALOG & DIGITAL SIGNALS

6. 3.PHASE
• This is the rate at which the signal changes its relationship to time,
expressed as degrees.
• One complete cycle of a wave begins at a certain point, and continues
till the same point is reached again.
• Phase shift occurs when the cycle does not complete, and a new cycle
begins before the previous one has fully completed.
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ANALOG & DIGITAL SIGNALS

7. PERIODIC SIGNAL (ANALOG SIGNAL)
• In data communication, we commonly use periodic
analog signals
• Periodic completes the wave within a same time frame
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ANALOG & DIGITAL SIGNALS

8. NON-PERIODIC SIGNAL (DIGITAL SIGNAL)
• and non-periodic digital signals,
• completes the wave with variable time
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ANALOG & DIGITAL SIGNALS

9. DIGITAL SIGNAL
• Digital signals are the language of modern day computers.
• Digital signals comprise only two states.
• These are expressed as ON or OFF, 1 or 0 respectively.
• Digital signals require greater bandwidth capacity than analogue signals,
thus are more expensive to communicate.
• This diagram shows a digital signal.
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ANALOG & DIGITAL SIGNALS

10. BIT RATE (Number of bit intervals per second )
• The bit rate describes the information-carrying capacity of a digital
channel, and is measured in bits per second (b/s).
• The range of frequencies in a channel is called its bandwidth.
• Roughly:
a higher-bandwidth channel has a higher bit rate.
Bit Interval(the time required to send one bit) 10
ANALOG & DIGITAL SIGNALS

11. NON-PERIODIC SIGNAL (DIGITAL SIGNAL)
• and non-periodic digital signals,
• completes the wave with variable time
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ANALOG & DIGITAL SIGNALS