Definition of Analog Signal

8/2/2019 Definition ofAnalog Signal

1/43

Analog Communication

UNIT I

Made by: Hridesh Vishwdewa


2/43

Definition of Analog Signal

Unlike a digital signal, which has a discrete value at eachsampling point, an analog signal has constant fluctuations.

The illustration in the above figure shows an analog pattern(represented as the curve) alongside a digital pattern(represented as the discrete lines).

An analog signal is acontinuous signal that containstime-varying quantities.


3/43

An analog signal can be used to measure changes in somephysical phenomena such as light, sound, pressure, ortemperature.

For instance, an analog microphone can convert soundwaves into an analog signal.

Even in digital devices, there is typically some analogcomponent that is used to take in information from the

external world, which will then get translated into digital form(using an analog-to-digital converter).


4/43

Systems

A System, is any physical set of componentsthat takes a signal, and produces a signal. Interms of engineering, the input is generally some

electrical signal X, and the output is anotherelectrical signal (response) Y.

However, this may not always be the case.Consider a household thermostat, which takes

input in the form of a knob or a switch, and inturn outputs electrical control signals for thefurnace.


5/43

Classification of Systems

Continuous vs. Discrete

Linear vs. Nonlinear

Time Invariant vs. Time Varying

Causal vs. Noncausal

Stable vs. Unstable


6/43

Continuous vs. Discrete

One of the most important distinctions to understand isthe difference between discrete time and continuoustime systems.

A system in which the input signal and output signal both

have continuous domains is said to be a continuoussystem. One in which the input signal and output signalboth have discrete domains is said to be a continuoussystem.

Of course, it is possible to conceive of signals thatbelong to neither category, such as systems in whichsampling of a continuous time signal or reconstructionfrom a discrete time signal take place.


7/43

Linear vs. Nonlinear

A linear system is any system that obeys the propertiesof scaling (first order homogeneity) and superposition(additivity) further described below. A nonlinear systemis any system that does not have at least one of these

properties.

To show that a system obeys the scaling property is toshow that


8/43


9/43


10/43


11/43


12/43


13/43

Block

Diagram

of Comm.system

A: The information signal to be transmitted (Voice, music, DC to representrudder position in Radio Control).B: Digitally compressed data. Analogue filtering and compression is possibletoo.C: The low power radio frequency carrier signal.

D: The modulated carrier. The carrier has been modified in proportion to thesignal to be transmitted.E: High power signal, usually radio, but light and ultrasound are common too.F: Attenuated signal. Energy is lost in the transmission medium.G: Amplified signal.

H: A low power copy of the original compressed signal.I: An exact copy of the original information signal.


14/43

Types Of Signals

Continuous-Time vs. Discrete-Time

Analog vs. Digital

Periodic vs. Aperiodic

Finite vs. Infinite Length

Causal vs. Anticausal vs. Noncausal

Even vs. Odd Deterministic vs. Random


15/43

Continuous-Time vs. Discrete-Time

As the names suggest, this classification is determinedby whether or not the time axis isdiscrete (countable)or continuous (Figure 1). A continuous-time signal willcontain a value for all real numbers along the time axis.

In contrast to this, a discrete-time signal, often createdby sampling a continuous signal, will only have values at

equally spaced intervals along the time axis.
http://cnx.org/content/m10057/latest/http://cnx.org/content/m0009/latest/http://cnx.org/content/m0009/latest/http://cnx.org/content/m0009/latest/http://cnx.org/content/m0009/latest/http://cnx.org/content/m10057/latest/


16/43

Analog vs. Digital

The difference between analog and digital is similar to thedifference between continuous-time and discrete-time.However, in this case the difference involves the values of thefunction.

Analog corresponds to a continuous set of possible function

values, while digital corresponds to a discrete set of possiblefunction values.

A common example of a digital signal is a binary sequence,where the values of the function can only be one or zero.


17/43

Periodic vs. Aperiodic Periodic signals repeat with some periodT, while aperiodic,

or non-periodic, signals do not (Figure 3). We can define aperiodic function through the following mathematicalexpression, where tcan be any number and Tis a positiveconstant: f(t)=f(T+t) ----Eq.(1)

The fundamental period of our function, f(t), is the smallestvalue of Tthat the still allows Eq(1) to be true.
http://cnx.org/content/m10744/latest/http://cnx.org/content/m10057/latest/http://cnx.org/content/m10057/latest/http://cnx.org/content/m10744/latest/


18/43

Finite vs. Infinite Length As the name implies, signals can be characterized as to

whether they have a finite or infinite length set of values. Most

finite length signals are used when dealing with discrete-timesignals or a given sequence of values. Mathematicallyspeaking, ft is afinite-length signal if it is nonzero over a finiteinterval t 1 and t 2


19/43

Causal vs. Anticausal vs. Noncausal

Causal signals are signals that are zero for all negative time,

while anticausal are signals that are zero for all positivetime.Noncausal signals are signals that have nonzero values inboth positive and negative time Fig.5(a-c)


20/43

Even vs. Odd

An even signal is any signal fsuch that f(t)

= f(t). Even signals can be easily spottedas they are aymmetric around the verticalaxis. An odd signal, on the other hand, is asignal fsuch that f(t) = f(t) , Fig.6

Using the definitions of even and oddsignals, we can show that any signal can bewritten as a combination of an even andodd signal. That is, every signal has anodd-even decomposition. To demonstratethis, we have to look no further than a

single equation.

f(t) = (f(t) + f(t) ) + ( f(t) f(t))


21/43

Deterministic vs. Random A deterministic signal is a signal in which each value of the signal is fixed

and can be determined by a mathematical expression, rule, or table.

Because of this the future values of the signal can be calculated from pastvalues with complete confidence. On the other hand, a random signal has alot of uncertainty about its behavior. The future values of a random signalcannot be accurately predicted and can usually only be guessed based onthe averages of sets of signals (Figure 8).
http://cnx.org/content/m10649/latest/http://cnx.org/content/m10656/latest/http://cnx.org/content/m10057/latest/http://cnx.org/content/m10057/latest/http://cnx.org/content/m10656/latest/http://cnx.org/content/m10649/latest/


22/43

Example

Consider the signal defined for allreal tdescribed by -

F(t) = { sin (2t) / t } 0 t 1 t< 1

This signal is continuous time, analog,aperiodic, infinite length, causal, neither evennor odd, and, by definition, deterministic

I C i Ti


23/43

Important Continuous Time

Signals

Sinusoids

Complex Exponentials

Unit Impulses

Unit Step


24/43

Sinusoids One of the most important elemental signal that you will deal

with is the real-valued sinusoid. In its continuous-time form, wewrite the general expression as -


25/43

Complex Exponentials

As important as the general sinusoid,the complex exponential function willbecome a critical part of your study of

signals and systems. Its generalcontinuous form is written as -

A est

where s= +j is a complex number interms of , the attenuation constant,and the angular frequency.


26/43

Unit Impulses

The unit impulse function, also known as the Diracdelta function, is a signal that has infinite height andinfinitesimal width. However, because of the way itis defined, it integrates to one.

While this signal is useful for the understanding ofmany concepts, a formal understanding of itsdefinition more involved. The unit impulse iscommonly denoted ( t).

For now, it suffices to say that this signal is cruciallyimportant in the study of continuous signals, as itallows the sifting property to be used in signalrepresentation and signal decomposition.


27/43

Unit Step

Another very basic signal is the unit-step function thatis defined as -

The step function is a

useful tool for testing and fordefining other signals. Forexample, when differentshifted versions of the step

function are multiplied byother signals, one can selecta certain portion of the signaland zero out the rest.


28/43

Transmission Media A transmission medium (plural transmission media) is a

material substance (solid, liquid, gas, or plasma) thatcan propagateenergy-waves. For example, thetransmission medium for sound received by the ears isusually air, but solids and liquids may also act as

transmission media for sound. The term transmission medium also refers to a technical

device that employs the material substance to transmit orguide waves. Thus, an optical fiber or a copper cable is atransmission medium. Not only this bt also is able to guide

the transmission of networks.
http://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Gashttp://en.wikipedia.org/wiki/Plasma_(physics)http://en.wikipedia.org/wiki/Wave_propagationhttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Wavehttp://en.wikipedia.org/wiki/Soundhttp://en.wikipedia.org/wiki/Soundhttp://en.wikipedia.org/wiki/Wavehttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Wave_propagationhttp://en.wikipedia.org/wiki/Plasma_(physics)http://en.wikipedia.org/wiki/Gashttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Solid


29/43

A transmission medium can be classified as a:

Linear medium, if different waves at any particular point inthe medium can be superposed;

Bounded medium, if it is finite in extent,otherwise unbounded medium;

Uniform mediumor homogeneous medium, if its physicalproperties are unchanged at different points;

Isotropic medium, if its physical properties are the same indifferent directions.
http://en.wikipedia.org/wiki/Superposition_principlehttp://en.wikipedia.org/wiki/Superposition_principle


30/43

Transmission Media - Guided & Unguided

Guided Transmission Media uses a "cabling" system that

guides the data signals along a specific path. The datasignals are bound by the "cabling" system. Guided Media isalso known as Bound Media. Cabling is meant in a genericsense in the previous sentences and is not meant to be

interpreted as copper wire cabling only. Unguided Transmission Media consists of a means for the

data signals to travel but nothing to guide them along aspecific path. The data signals are not bound to a cabling

media and as such are often called Unbound Media. There 4 basic types of Guided Media:

1. Open Wire 2.Twisted Pair 3. Coaxial Cable 4.OpticalFiber


31/43

Open Wire

Open Wire is traditionally used to describe the electrical wire strung along

power poles. There is a single wire strung between poles. No shielding orprotection from noise interference is used.

We are going to extend the traditional definition of Open Wire to include anydata signal path without shielding or protection from noise interference.

This can include multi-conductor cables or single wires. This media issusceptible to a large degree of noise and interference and consequently not

acceptable for data transmission except for short distances under 20 ft.


32/43

Twisted Pair

The wires in Twisted Pair cabling are twisted together in pairs. Each pairwould consist of a wire used for the +ve data signal and a wire used for the -

ve data signal.

Any noise that appears on 1 wire of the pair would occur on the other wire.Because the wires are opposite polarities, they are 180 degrees out ofphase (180 degrees - phasor definition of opposite polarity). When the noiseappears on both wires, it cancels or nulls itself out at the receiving end.

Twisted Pair cables are most effectively used in systems that use abalanced line method of transmission: polar line coding (ManchesterEncoding) as opposed to unipolar line coding (TTL logic).


33/43

Twisted Pair

The degree of reduction in noise interference is determined

specifically by the number of turns per foot. Increasing thenumber of turns per foot reduces the noise interference.

To further improve noise rejection, a foil or wire braid shield iswoven around the twisted pairs.

This "shield" can be woven around individual pairs or around amulti-pair conductor (several pairs).


34/43

Cables with a shield are called Shielded Twisted Pair and commonlyabbreviated STP. Cables without a shield are called UnshieldedTwisted Pair or UTP. Twisting the wires together results in acharacteristic impedance for the cable. A typical impedance for UTPis 100 ohm for Ethernet 10BaseT cable.

UTP or Unshielded Twisted Pair cable is used on Ethernet 10BaseT

and can also be used with Token Ring. It uses the RJ line ofconnectors (RJ45, RJ11, etc..)

STP or Shielded Twisted Pair is used with the traditional Token Ringcabling or ICS - IBM Cabling System. It requires a custom

connector. IBM STP (Shielded Twisted Pair) has a characteristicimpedance of 150 ohms.


35/43

Coaxial Cable Coaxial Cable consists of 2 conductors. The inner conductor is held inside

an insulator with the other conductor woven around it providing a shield.

An insulating protective coating called a jacket covers the outer conductor.

The outer shield protects the inner conductor from outside electrical signals.The distance between the outer conductor (shield) and inner conductor plus

the type of material used for insulating the inner conductor determine thecable properties or impedance. Typical impedances for coaxial cables are 75ohms for Cable TV, 50 ohms for Ethernet Thinnet and Thicknet. The excellentcontrol of the impedance characteristics of the cable allow higher data ratesto be transferred than Twisted Pair cable.


36/43

Optical Fibre Optical Fibre consists of thin glass fibres that can carry information at

frequencies in the visible light spectrum and beyond. The typical opticalfibre consists of a very narrow strand of glass called the Core. Around theCore is a concentric layer of glass called the Cladding. A typical Corediameter is 62.5 microns (1 micron = 10-6 meters). Typically Cladding hasa diameter of 125 microns. Coating the cladding is a protective coating

consisting of plastic, it is called the Jacket.


37/43

Optical Fibre

An important characteristic of Fibre Optics is Refraction. Refractionis the characteristic of a material to either pass or reflect light. Whenlight passes through a medium, it "bends" as it passes from onemedium to the other. An example of this is when we look into a pondof water.

Optical Fibres work on the principle that the core refractsthe light and the cladding reflects the light. The corerefracts the light and guides the light along its path. Thecladding reflects any light back into the core and stops

light from escaping through it - it bounds the media!


38/43

Optical Fiber


39/43

Radio Waves Radio waves are a type of electromagnetic radiation with wavelengths in

the electromagnetic spectrum longer than infrared light. Radio waves

have frequencies from 300 GHz to as low as 3 kHz, and correspondingwavelengths from 1 millimeter to 100 kilometers. Like all otherelectromagnetic waves, they travel at the speed of light.

Naturally occurring radio waves are made by lightning, or by astronomical

objects. Artificially generated radio waves are used for fixed andmobile radio communication, broadcasting, radar and other navigationsystems, satellite communication, computer networks and innumerable otherapplications
http://en.wikipedia.org/wiki/Electromagnetic_radiationhttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Electromagnetic_spectrumhttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Gigahertzhttp://en.wikipedia.org/wiki/Kilohertzhttp://en.wikipedia.org/wiki/Speed_of_lighthttp://en.wikipedia.org/wiki/Lightninghttp://en.wikipedia.org/wiki/Radio_astronomyhttp://en.wikipedia.org/wiki/Radio_astronomyhttp://en.wikipedia.org/wiki/Radio_communicationhttp://en.wikipedia.org/wiki/Broadcastinghttp://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Broadcastinghttp://en.wikipedia.org/wiki/Radio_communicationhttp://en.wikipedia.org/wiki/Radio_astronomyhttp://en.wikipedia.org/wiki/Radio_astronomyhttp://en.wikipedia.org/wiki/Lightninghttp://en.wikipedia.org/wiki/Speed_of_lighthttp://en.wikipedia.org/wiki/Kilohertzhttp://en.wikipedia.org/wiki/Gigahertzhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Electromagnetic_spectrumhttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Electromagnetic_radiation


40/43

Micro Waves

Microwaves are radio waves with wavelengths ranging from as long as

one meter to as short as one millimeter, or equivalently,with frequencies between 300 MHz (0.3 GHz) and 300 GHz.

This broad definition includes both UHF and EHF (millimeter waves), andvarious sources use different boundaries.[2] In all cases, microwave

includes the entire SHF band (3 to 30 GHz, or 10 to 1 cm) at minimum,with RF engineering often putting the lower boundary at 1 GHz (30 cm),and the upper around 100 GHz (3 mm).

I f d T i i
http://en.wikipedia.org/wiki/Radio_waveshttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Ultra_high_frequencyhttp://en.wikipedia.org/wiki/Extremely_high_frequencyhttp://en.wikipedia.org/wiki/Millimeter_wavehttp://en.wikipedia.org/wiki/Microwavehttp://en.wikipedia.org/wiki/Super_high_frequencyhttp://en.wikipedia.org/wiki/RF_engineeringhttp://en.wikipedia.org/wiki/RF_engineeringhttp://en.wikipedia.org/wiki/Super_high_frequencyhttp://en.wikipedia.org/wiki/Microwavehttp://en.wikipedia.org/wiki/Millimeter_wavehttp://en.wikipedia.org/wiki/Extremely_high_frequencyhttp://en.wikipedia.org/wiki/Ultra_high_frequencyhttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Radio_waves


41/43

Infrared Transmission

Infrared transmission refers to energy in the region of the electromagneticradiation spectrum at wavelengths longer than those of visible light, but

shorter than those of radio waves. Correspondingly, infrared frequencies arehigher than those of microwaves, but lower than those of visible light.

Scientists divide the infrared radiation (IR) spectrum into three regions.

The wavelengths are specified in microns (symbolized , where 1 = 10-6 meter) or in nanometers (abbreviated nm, where 1 nm = 10-9 meter =0.001 5).

The near IR bandcontains energy in the range of wavelengths closest to the

visible, from approximately 0.750 to 1.300 5 (750 to 1300 nm).

The intermediate IR band(also called the middle IR band) consists ofenergy in the range 1.300 to 3.000 5 (1300 to 3000 nm). The far IRbandextends from 2.000 to 14.000 5 (3000 nm to 1.4000 x 104 nm).
http://searchcio-midmarket.techtarget.com/definition/electromagnetic-radiation-spectrumhttp://searchcio-midmarket.techtarget.com/definition/electromagnetic-radiation-spectrumhttp://searchnetworking.techtarget.com/definition/wavelengthhttp://searchnetworking.techtarget.com/definition/wavelengthhttp://searchcio-midmarket.techtarget.com/definition/electromagnetic-radiation-spectrumhttp://searchcio-midmarket.techtarget.com/definition/electromagnetic-radiation-spectrum


42/43

Infrared is used in a variety of wireless communications,monitoring, and control applications. Here are someexamples:

1. Home-entertainment remote-control boxes2. Wireless (local area networks)3. Links between notebook computers and desktop computers4. Cordless modem

5. Intrusion detectors6. Motion detectors7. Fire sensors8. Night-vision systems9. Medical diagnostic equipment10.Missile guidance systems

11.Geological monitoring devices
http://searchmobilecomputing.techtarget.com/definition/wirelesshttp://searchmobilecomputing.techtarget.com/definition/modemhttp://searchmobilecomputing.techtarget.com/definition/modemhttp://searchmobilecomputing.techtarget.com/definition/wireless


43/43

Bye-Bye

Definition of Analog Signal

Documents

Transcript of Definition of Analog Signal