fy bsc-it communication

06/09/2011

dalviarun@rediffmail.com

Semester II

• Mathematics I

• Fundamentals of Digital Computing

• Electronics and Tele Communication Systems

• Professional Communication Skill

• Programming with C++

CLASS: B. Sc (Information technology)

Semester – I

SUBJECT: Electronics and Communication Technology (USIT104)

Periods per week Lectures - 5 3 Credits

06/09/2011

ELECTRONICS• Unit – I• Concept of Conductor, Semiconductor, Insulator.

Semiconductor Diode, Forward bias, Reverse Bias, Application of Diode as Rectifier, Zener diode and its applications, Introduction to Transistor (BJT, FET), PNP, NPN Transistors their Characteristic. Application of Transistor as amplifier and as a Switch.

• Unit- II• Concept of amplification, amplifier notations, Av, Ai, Ap Zi, Zo),

Application of BJT as single stage Amplifier, Frequency response of single stage Amplifier. Multistage Amplifiers:-(Basics concepts) RC coupled, cascade, Darlington pair, DC amplifiers.

• Unit-III• Concept of Feedback:- Negative Feedback and its advantage

in Amplification, Positive Feedback :- Oscillators, RC Phase Shift Oscillator, LC Oscillator. Switching Circuits Multivibrators :

06/09/2011

COMMUNICATION TECHNOLOGY• Unit- IV

• Introduction:- Need for modulation system, Concept of Modulation. AM :-Definition of AM, Modulation index, Power relation in AM, Generation and Demodulation of AM. SSB:- Power requirement in comparison with AM, Advantages of SSB over AM, Concept of Balanced Modulator, Generation of SSB, Pilot Carrier System, Independent Side System, Vestigial Sideband Transmission.

• Unit- V

• FM: - Definition of FM, Bandwidth, Noise triangle, Per-emphasis and De-emphasis. PM: - Definition of PM. Difference between AM and FM. Radio receivers. Pulse Modulation:- Sampling Theorem, PAM, PTM, PWM, PPM, pulse code modulation, Quantization noise, companding, PCM system, differential PCM, Delta modulation. Multiplexing: - FDM/TDM. Television:-Scanning, Composite Video signal, Television Transmitter, television receiver.

• Unit-VI• Introduction to Digital Communication: PSK, ASK, FSK. • Introduction to fibre optics system:- Propagation of light in optical fibre; ray

model . Types of fibre : Single mode, steps index. Graded index. Signal

• Boylstead and Neshelesky , “Electronics Devices and Circuits”, 4th , PHI, 1999.

• Data communication & networking by Behroz Forouzan, 3rd edition

06/09/2011

Signals

Leads to

Information

Leads to

Signal

Note:Note:

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To be transmitted, data must be transformed to electromagnetic

signals.

Note:Note:

3.1 Analog and Digital

Analog and Digital Data

Analog and Digital Signals

Periodic and Aperiodic Signals

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Signals can be analog or digital. Analog signals can have an infinite number of values in a range; digital

signals can have only a limited number of values.

Note:Note:

Figure 3.1 Comparison of analog and digital signals

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In data communication, we commonly use periodic analog signals and

aperiodic digital signals.

Note:Note:

3.2 Analog Signals

Sine WavePhaseExamples of Sine WavesTime and Frequency DomainsComposite SignalsBandwidth

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Figure 3.2 A sine wave

Figure 3.3 Amplitude

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Frequency and period are inverses of each other.

Note:Note:

Figure 3.4 Period and frequency

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Table 3.1 Units of periods and frequenciesTable 3.1 Units of periods and frequencies

Unit Equivalent Unit Equivalent

Seconds (s) 1 s hertz (Hz) 1 Hz

Milliseconds (ms) 10–3 s kilohertz (KHz) 103 Hz

Microseconds (ms) 10–6 s megahertz (MHz) 106 Hz

Nanoseconds (ns) 10–9 s gigahertz (GHz) 109 Hz

Picoseconds (ps) 10–12 s terahertz (THz) 1012 Hz

Example 1Example 1

Express a period of 100 ms in microseconds, and express the corresponding frequency in kilohertz.

SolutionSolution

From Table 3.1 we find the equivalent of 1 ms.We make the following substitutions:100 ms = 100 × 10-3 s = 100 × 10-3 × 106 µs = 105 µs

Now we use the inverse relationship to find the frequency, changing hertz to kilohertz100 ms = 100 × 10-3 s = 10-1 s f = 1/10-1 Hz = 10 × 10-3 KHz = 10-2 KHz

06/09/2011

Frequency is the rate of change with respect to time. Change in a short span of time means high frequency. Change

over a long span of time means low frequency.

Note:Note:

If a signal does not change at all, its frequency is zero. If a signal changes

instantaneously, its frequency is infinite.

Note:Note:

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Phase describes the position of the waveform relative to time zero.

Note:Note:

Figure 3.5 Relationships between different phases

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Example 2Example 2

A sine wave is offset one-sixth of a cycle with respect to time zero. What is its phase in degrees and radians?

SolutionSolution

We know that one complete cycle is 360 degrees.

Therefore, 1/6 cycle is

(1/6) 360 = 60 degrees = 60 x 2π /360 rad = 1.046 rad

Figure 3.6 Sine wave examples

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Figure 3.6 Sine wave examples (continued)

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An analog signal is best represented in the frequency domain.

Note:Note:

Figure 3.7 Time and frequency domains (continued)

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Figure 3.7 Time and frequency domains (continued)

A single-frequency sine wave is not useful in data communications; we need to change one or more of its characteristics to make it useful.

Note:Note:

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When we change one or more When we change one or more characteristics of a singlecharacteristics of a single--frequency frequency signal, it becomes a composite signal signal, it becomes a composite signal

made of many frequencies.made of many frequencies.

Note:Note:

According to Fourier analysis, any composite signal can be represented as

a combination of simple sine waves with different frequencies, phases, and

amplitudes.

Note:Note:

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Figure 3.12 Signal corruption

The bandwidth is a property of a The bandwidth is a property of a medium: It is the difference between medium: It is the difference between

the highest and the lowest frequencies the highest and the lowest frequencies that the medium can that the medium can satisfactorily pass.satisfactorily pass.

Note:Note:

06/09/2011

In this book, we use the term In this book, we use the term bandwidth to refer to the property of a bandwidth to refer to the property of a

medium or the width of a single medium or the width of a single spectrum.spectrum.

Note:Note:

Figure 3.13 Bandwidth

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Example 3Example 3

If a periodic signal is decomposed into five sine waves with frequencies of 100, 300, 500, 700, and 900 Hz, what is the bandwidth? Draw the spectrum, assuming all components have a maximum amplitude of 10 V.

SolutionSolution

B = fh − fl = 900 − 100 = 800 HzThe spectrum has only five spikes, at 100, 300, 500, 700, and 900 (see Figure 13.4 )

Example 4Example 4

A signal has a bandwidth of 20 Hz. The highest frequency is 60 Hz. What is the lowest frequency? Draw the spectrum if the signal contains all integral frequencies of the same amplitude.

SolutionSolution

B = fB = fhh −− ffll

20 = 60 20 = 60 −− ffll

ffll = 60 = 60 −− 20 = 40 Hz20 = 40 Hz

06/09/2011

Example 5Example 5

A signal has a spectrum with frequencies between 1000 and 2000 Hz (bandwidth of 1000 Hz). A medium can pass frequencies from 3000 to 4000 Hz (a bandwidth of 1000 Hz). Can this signal faithfully pass through this medium?

SolutionSolution

The answer is definitely no. Although the signal can have The answer is definitely no. Although the signal can have the same bandwidth (1000 Hz), the range does not the same bandwidth (1000 Hz), the range does not overlap. The medium can only pass the frequencies overlap. The medium can only pass the frequencies between 3000 and 4000 Hz; the signal is totally lost.between 3000 and 4000 Hz; the signal is totally lost.

3.3 Digital Signals3.3 Digital Signals

Bit Interval and Bit RateAs a Composite Analog SignalThrough Wide-Bandwidth MediumThrough Band-Limited MediumVersus Analog BandwidthHigher Bit Rate

06/09/2011

Figure 3.16 A digital signal

Example 6Example 6

A digital signal has a bit rate of 2000 bps. What is the duration of each bit (bit interval)

SolutionSolution

The bit interval is the inverse of the bit rate.

Bit interval = 1/ 2000 s = 0.000500 s = 0.000500 x 106 µs = 500 µs

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Figure 3.17 Bit rate and bit interval

Figure 3.18 Digital versus analog

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A digital signal is a composite signal A digital signal is a composite signal with an infinite bandwidth.with an infinite bandwidth.

Note:Note:

Table 3.12 Bandwidth RequirementTable 3.12 Bandwidth Requirement

BitRate

Harmonic1

Harmonics1, 3

Harmonics1, 3, 5

Harmonics1, 3, 5, 7

1 Kbps 500 Hz 2 KHz 4.5 KHz 8 KHz

10 Kbps 5 KHz 20 KHz 45 KHz 80 KHz

100 Kbps 50 KHz 200 KHz 450 KHz 800 KHz

06/09/2011

The bit rate and the bandwidth are The bit rate and the bandwidth are proportional to each other.proportional to each other.

Note:Note:

3.4 Analog versus Digital3.4 Analog versus Digital

Low-pass versus Band-pass

Digital Transmission

Analog Transmission

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3.6 Transmission Impairment3.6 Transmission Impairment

Attenuation

Distortion

Figure 3.20 Impairment types

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Figure 3.21 Attenuation

Figure 3.23 Distortion

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Figure 3.24 Noise

3.7 More About Signals3.7 More About Signals

Throughput

Propagation Speed

Propagation Time

Wavelength

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Figure 3.25 Throughput

Figure 3.26 Propagation time

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Figure 3.27 Wavelength

Digital-to-analog modulation

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Figure 5.2 Types of digital-to-analog modulation

Figure 5.3 ASK

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Figure 5.6 FSK

Figure 5.8 PSK

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Figure 5.9 PSK constellation

Figure 5.10 The 4-PSK method

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Figure 5.11 The 4-PSK characteristics

Figure 5.12 The 8-PSK characteristics

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Figure 5.14 The 4-QAM and 8-QAM constellations

Figure 5.15 Time domain for an 8-QAM signal

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Analog Analog ––to to -- AnalogAnalog

Amplitude Modulation (AM)

Frequency Modulation (FM)

Phase Modulation (PM)

Figure 5.24 Analog-to-analog modulation

06/09/2011

Figure 5.25 Types of analog-to-analog modulation

The total bandwidth required for AM can be determined from the bandwidth

of the audio signal: BWt = 2 x BWm.

Note:Note:

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Figure 5.26 Amplitude modulation

Figure 5.27 AM bandwidth

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Figure 5.29 Frequency modulation

Telecommunication Systems

06/09/2011

BASIC COMMUNICATION SYSTEM

BLOCK DIAGRAM FOR BASIC COMMUNICATION SYSTEM

INFORMATION OR

i/p SIGNALINPUT

TRANSDUCERTRANSMITTER

COMMUNICATION CHANNEL

OR MEDIUM

RECEIVER OUTPUTTRANSDUCER

Classification of communication systems• Whether the system is unidirectional or bidirectional

• Whether it uses an analog or digital information signal• Whether the system uses baseband transmission or

uses some kind of modulation

DIRECTION NATURE OF THE SIGNAL

TECHNIQUE OF

TRANSMISSION

SIMPLEX HALF DUPLEX

FULL DUPLEX

ANALOG

DIGITAL BASEBAND

MODULATION

06/09/2011

Bending of light ray

Optical fiber

06/09/2011

Figure 7.12 Propagation modes

Figure 7.13 Modes

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Table 7.3 Fiber typesTable 7.3 Fiber typesType Core Cladding Mode

50/12550/125 50 125Multimode, graded-

62.5/12562.5/125 62.5 125 Multimode, graded-index

100/125100/125 100 125Multimode, graded-

7/1257/125 7 125 Single-mode

Figure 7.14 Fiber construction

06/09/2011

Figure 7.15 Fiber-optic cable connectors

Why we need Modulation?

• To reduce the height of antenna• To avoid mixing of signals (distortion)• To increase the range of

communication(attenuation )• To make multiplexing possible• To improve quality of reception

06/09/2011

To reduce the height of antenna

• As per the Standards, for the transmission of radio signals, the antenna height must be multiple of ( ?/4)

• Here ? is wavelength. And ?=c/f• C= velocity of light • F = frequency of the signal to be transmitted

• So for f = 10kHz signals to get transmitted, we need:

• Height of antenna= ?/4 = c/4f

-------------- = 7500 meters=7.5km4x 10x103

Is it possible?dalviarun@rediffmail.com

06/09/2011

• Now assume the signal of frequency 1MHz. And do the calculation.

Height of antenna= ?/4 = c/4f

-------------- = 75 meters4x 1x106

Is it possible?dalviarun@rediffmail.com

To make multiplexing possible

fy bsc-it communication

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