adc 02 noise in communication

ANALOG & DIGITAL COMMUNICATION

By Engr. Hyder Bux MangrioInstitute of Information & Communication Technologies

Mehran University of Engineering and Technology, Jamshoro.

09TL-BATCH

Today's Lecture:3-4

Noise in Communication

04/10/23 [email protected]

Introduction

Any electrical signal transmitted from one point to another can ultimately be classified as having two parts:

one that represents the original intelligence, the desirable part; and the undesirable part which we call NOISE

In all telecommunication systems, the effect of noise superimposed on the original intelligence is of major concern to us.

04/10/23 [email protected] 2

Introduction

Noise in communication originates both in the channel and communication equipments.

Noise consists of undesired usually random variations that interfere with desired signal.

It cannot be avoided completely, but its effects can be reduced by various mean such as reducing the signal bandwidth, increase the transmitter power using low noise amplifier for weak signal.


Types of Noise

There are two types of Noise

1. Correlated Noise

2. Uncorrelated Noise Correlation implies a relationship between the

signal and the noise. Correlated noise exits only when a signal is

present.


Uncorrelated Noise

Uncorrelated noise, on the other hand is present all the time whether the signal is present or not.


Types of Uncorrelated Noise

I. External Noise

II. Internal Noise External Noise: which is property of channel If the channel is a radio link, there are many

possible source of noise Interference from automobile ignition systems The three primary sources of external noise are

atmospheric, extraterrestrial and Man-made


Types of Noise

Internal Noise: which originates within the communication equipment.

Equipment Noise: Noise generated by equipment that produce sparks Any fast rise time voltage or current can also generates

interference. Noise of this type has a broad frequency spectrum, but

its energy is equally distributed over the range of frequencies.

This types of interference is generally more severe at low frequencies.


Types of NoiseAtmosphere Noise: Atmospheric noise is naturally occurring electrical

disturbances that originates within Earth’s atmosphere. Atmosphere noise is often called static because of

lightning, which is a static electricity discharge. Most of energy of lightning is found at relatively low

frequencies, up to several MHz. Effective circuits are used to reduce the noise.


Extraterrestrial Noise(EXTN)

Consists of electrical signals that originate from outside Earth atmosphere

Also known as deep space noise Extraterrestrial noise originates from milky

way, galaxies and the sun. EXTN is subdivided into two categories

I. Solar Noise

II. Cosmic Noise


Types of Noise

Space Noise: The sun is a powerful source of radiation over a wide

range of frequencies. Other stars also radiates noise called cosmic, stellar or

sky noise. Solar noise can be a serious problem for satellite

reception.


Man-made Noise is simply noise that is produced by mankind Predominated sources of man-made noise are

spark-producing mechanisms such as Commutators in electric motors Automobile ignition systems ac power generators Switching equipment

Man-made noise is most intense in the more densely populated metropolitan and industrial areas. Also known as Industrial noise.


Types of Noise

Gaussian Noise: The cumulative effect of all random noise generated external or internal to the telecommunication system, averaged over a period of time is referred to as Gaussian noise.

Gaussian noise includes all frequencies. Thermal Noise: Gaussian noise is more specifically

referred to as white noise, thermal noise or Johnson noise.

Noise generated by the random motion of free electrons and molecular vibrations exhibited by all electronics components.


Types of Noise

Random motion results in frequency components that are evenly distributed over entire radio spectrum. Also known as white noise.

All resistive components are constant noise generators. In 1928 J. B. Johnson a US physicist, demonstrated

that resistive components generate noise power is proportion to both temperature and bandwidth.


Types of Noise

BWTKPn ..

Where K= Boltzmann’s constant of 1.38x10-23 J/K T= absolute temperature of the device(Ko)BW= circuit bandwidthPn= noise power output of the resistor

Ln R

V

R

VBWTKP

22

..

RBWTKVn ...404/10/23 [email protected]

EXAMPLE:2.5

An amplifier used to process an FDM channel group(12 voice channels) operates over a frequency range from 60 to 108 KHz. The input impedance has a resistive component of 10KΩ. Compute the equivalent noise voltage at the input of the amplifier at an operating temperature of 24oC.

Solution: oK= 273+oC = 273+24=297

BW= 108KHz-60KHz= 48KHz

3323 101010482971038.14...4 xxxxxxxRBWTKVn

Vn= 2.81µV04/10/23 [email protected]

Problem

For an electronic device operating at a temperature of 170C with a bandwidth of 10kHz, determine

a) Thermal noise power

b) Rms noise voltage for a 100Ω internal resistance and a 100Ω load resistance.


Types of Noise

Shot Noise: Another significant contributor to the distribution of

Gaussian noise is shot noise. originates from the sound that it produces at the audio

output of a receiver. Noise generated as the result of the random arrival rate

of discrete current carriers(holes or electrons) at the output of semiconductor device.


Types of Noise

This randomness generates the noise currents associated with shot noise.

For semiconductor device, this current is equal to

qIfin 2Where in = shot noise current in rms

q= charge of an electron, 1.6x10-19 C I= DC current flowing through the device(A) f= system bandwidth (Hz)


Types of Noise

Impulse noise Impulse noise is characterized by high

amplitude peaks of short duration in total noise spectrum.

Impulse noise consists of sudden bursts of irregularly shaped pulses

Common source of IN include transients produced from electromechanical switches, electric motors, appliances, electric lights, power lines, poor quality soldering joints etc


Correlated Noise

Correlated noise is a form of internal noise is produce by non-linear amplification and

include harmonic and intermodulation distortion

Also known as non-linear distortion. Harmonic distortion occurs when unwanted

harmonics of a signal are produce through nonlinear amplification.


Correlated Noise

Intermodulation distortion is the generation of unwanted sum and difference frequencies produced when two and more signals mix in nonlinear device.

The sum and difference frequencies are called cross product

Cross products = mf1 ± nf2


adc 02 noise in communication

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