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# Analog and Digital Signals

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• (named in honor of Alexander Graham Bell)
• ### Analog and Digital Signals

1. 1. ANALOG ANDD I G I TA LSIGNALS By : SANA ULLAH
2. 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. 2ANALOG & DIGITAL SIGNALS
3. 3. ANALOG SIGNALSHow 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, 3ANALOG & DIGITAL SIGNALS
4. 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 Sound40db normal speech90db lawn mowers110db shotgun blast120db jet engine taking off120db+ rock concerts 4ANALOG & DIGITAL SIGNALS
5. 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. 5ANALOG & DIGITAL SIGNALS
6. 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. 6ANALOG & DIGITAL SIGNALS
7. 7. PERIODIC SIGNAL (ANALOG SIGNAL)• In data communication, we commonly use periodic analog signals• Periodic completes the wave within a same time frame 7ANALOG & DIGITAL SIGNALS
8. 8. NON-PERIODIC SIGNAL (DIGITAL SIGNAL)• and non-periodic digital signals,• completes the wave with variable time 8ANALOG & DIGITAL SIGNALS
9. 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. 9ANALOG & DIGITAL SIGNALS
10. 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) 10ANALOG & DIGITAL SIGNALS
11. 11. NON-PERIODIC SIGNAL (DIGITAL SIGNAL)• and non-periodic digital signals,• completes the wave with variable time 11ANALOG & DIGITAL SIGNALS