analog noise
DESCRIPTION
THIS IS A GOOD BOOKTRANSCRIPT
-
Analog
Communication6/13/2015 1Analog Communication - NOISE
-
Thi book is compiled by abhishek kumar
This book is compiled by abhishek kumar
6/13/2015 Analog Communication - NOISE 2
-
NOISE
3Analog Communication - NOISE6/13/2015
-
Topics to be covered
Noise
Sources of noise
Thermal Noise, Shot Noise, Flicker noise and White noise
Noise Parameters
Signal to noise ratio
Noise factor
Effective noise temperature
4Analog Communication - NOISE6/13/2015
-
Topics to be covered
Narrow band noise
Representation of narrowband noise in terms of In phase and Quadrature Components
Noise in CW modulation Systems
Noise in linear Receivers using Coherent detection
Noise in AM Receivers using Envelope detection
Noise in FM Receivers
6/13/2015 5Analog Communication - NOISE
-
Noise Sources Introduction to Noise
Shot Noise
Thermal Noise
Flicker Noise
White Noise
6/13/2015 6Analog Communication - NOISE
-
Noise - Introduction
Noise Unwanted Signals that tend to disturb theTransmission and Processing of Signals inCommunication System and over which we haveincomplete control.
Noise is a general term which is used to describean unwanted signal which affects a wanted signal.
These unwanted signals arise from a variety ofsources.
6/13/2015 7Analog Communication - NOISE
-
Sources of Noise
Sources of noise may be:
External
Internal
Naturally occurring external noise sources include:
Atmosphere disturbance (e.g. electric storms, lighting,ionospheric effect etc), so called Sky Noise
Cosmic noise which includes noise from galaxy, solarnoise
Hot spot due to oxygen and water vapour resonancein the earths atmosphere.
6/13/2015 8Analog Communication - NOISE
-
Sources of Noise
Noise performance by external sources is shown below.
6/13/2015 9Analog Communication - NOISE
-
Sources of Noise
Internal Noise is an important type of noise thatarises from the SPONTANEOUS FLUCTUATIONS ofCurrent or Voltage in Electrical Circuits.
This type of noise is the basic limiting factor ofemploying more complex Electrical Circuits inCommunication System.
Most Common Internal Noises are:
Shot Noise Thermal Noise
6/13/2015 10Analog Communication - NOISE
-
Shot Noise
Shot Noise arises in Electronic Components likeDiodes and Transistors.
Due to the discrete nature of Current flow Inthese components.
Take an example of Photodiode circuit.
Photodiode emits electrons from the cathodewhen light falls on it.
The circuit generates a current pulse when anelectron is emitted.
6/13/2015 11Analog Communication - NOISE
-
Shot Noise
The electrons are emitted at Random times, kwhere - < k < and assume this randomemission have been gone for a long time.
Thus the Total Current flowing through thePhotodiode may be modeled as the sum of theseCurrent Pulses.
This process X(t) is Stationary and is called SHOTNOISE
6/13/2015 12Analog Communication - NOISE
-
Thermal Noise
Thermal Noise is the name given to the Electrical Noise arisingfrom the Random motion of electrons n a conductor.
It is also called Jonson Noise or Nyquist Noise.
Let VTN is the Thermal Noise Voltage appearing across the twoterminals of a resistor.
Let the applied voltage have a bandwidth or frequency), f.
Then the Mean Square value of VTN is given by:
6/13/2015 13Analog Communication - NOISE
-
Thermal Noise
Where
k = Boltzmanns constant = 1.38 x 10-23 Joules per oK
T = absolute temperature in oK
R = resistance in ohms
6/13/2015 14Analog Communication - NOISE
-
Jonson Noise or Nyquist Noise
6/13/2015 15Analog Communication - NOISE
-
Thermal Noise
We can model a noisy resistor using the Thevenin andNorton Equivalent Circuit as shown below:
6/13/2015 16Analog Communication - NOISE
-
Thermal Noise
The number of electrons inside a resistor is verylarge and their random motions inside theresistors are statistically independent.
The Central Limiting Theorem indicates thatthermal Noise is a Gaussian Distribution with Zeromean.
6/13/2015 17Analog Communication - NOISE
abhishek kumarSticky Note this is a good book say thanks to me
-
Low Frequency or Flicker Noise
Active devices, integrated circuit, diodes, transistors etc also
exhibits a low frequency noise, which is frequency
dependent (i.e. non uniform) known as flicker noise .
It is also called one over f noise or 1/f noise because of
its low-frequency variation.
Its origin is believed to be attributable to contaminants and
defects in the crystal structure in semiconductors, and in
the oxide coating on the cathode of vacuum tube devices
6/13/2015 18Analog Communication - NOISE
-
Low Frequency or Flicker Noise
Flicker Noise is found in many natural phenomena such asnuclear radiation, electron flow through a conductor, oreven in the environment.
The noise power is proportional to the bias current, and,unlike Thermal and Shot Noise, Flicker Noise decreases withfrequency.
An exact mathematical model does not exist for flickernoise because it is so device-specific.
However, the inverse proportionality with frequency isalmost exactly 1/f for low frequencies, whereas forfrequencies above a few kilohertz, the noise power is weakbut essentially flat.
6/13/2015 19Analog Communication - NOISE
-
Low Frequency or Flicker Noise
Flicker Noise is essentially random, but because its frequencyspectrum is not flat, it is not a white noise.
It is often referred to as pink noise because most of the power isconcentrated at the lower end of the frequency spectrum.
Flicker Noise is more prominent in FETs (smaller the channel length,greater the Flicker Noise), and in bulky carbon resistors.
The objection to carbon resistors mentioned earlier for critical lownoise applications is due to their tendency to produce flicker noisewhen carrying a direct current.
In this connection, metal film resistors are a better choice for lowfrequency, low noise applications.
6/13/2015 20Analog Communication - NOISE
-
White Noise
The Noise Analysis of Communication System isdone on the basis of an idealized form of noisecalled WHITE NOISE.
Its power spectral density is independent onoperating frequency.
White White light contain equal amount of allfrequencies in visible spectrum.
6/13/2015 21Analog Communication - NOISE
-
White Noise
Power spectral density is given by:
The 1/2 here emphasizes that the spectrum extends to both positive and negative frequencies.
6/13/2015 22Analog Communication - NOISE
-
Power Spectral Density of White Noise
A random process W(t) is called white noise if it has a flat power spectral density, i.e., SW(f) is a constant c for all f.
6/13/2015 23Analog Communication - NOISE
-
Ideal Low Pass Filtered White Noise
Let
w(t) = White Gaussian Noise applied to the LPF
B = Bandwidth of LPF
n(t) = noise appearing at the output of LPF
SN(f) = Power Spectral Density of n(t)
RN() = Auto Correlation function of n(t)
6/13/2015 24Analog Communication - NOISE
-
Ideal Low Pass filtered White Noise
6/13/2015 25Analog Communication - NOISE