CHAPTER 1 Part 2.1  Noise

Objectives To differentiate the types of noise To calculate the thermal noise generated by a resistor To calculate the signal-to-noise ratio (SNR) and noise figure for an amplifier

Lecture overview Types of noise Thermal noise Signal-to-noise ration (SNR) and noise figure

Introduction Noise can be defined as undesired random variations that interface with the desired signal and inhibit communication. Where does noise originate in a communication system? Channel @ transmission medium Devices @ Equipments

Cont’d... Noise Effect One of the main limiting factor in obtaining high performance of a communication system. Decrease the quality of the receiving signal.

Block Diagram of Communication System With the Existence of Noise

Noise, interference and distortion Refers to random and unpredictable electrical signals produced by natural process. Superimposed on information bearing signal, the message partially corrupted or totally erased. Can be reduced by filtering but can’t totally eliminated.

Interference A contamination by extraneous signals from human sources (e.g. from other Tx, power lines, machineries) Often occurred in radio system whose Rx antenna intercept several signals at the same time.

Disappear when the signal is turned- off. Distortion The signal perturbation caused by imperfect response of the system to the desired signal. Disappear when the signal is turned- off. Can be corrected by the equalizers.

INCREASE TRANSMITTER’S Noise Remedies? REDUCE BANDWIDTH INCREASE TRANSMITTER’S POWER LOW NOISE AMPLIFIERS

Types of NOISE

EXTERNAL NOISE Noise generated outside the device or circuit. Three primary sources: Atmospheric noise. Extraterrestrial noise Man-made noise

EXTERNAL NOISE Atmospheric noise Naturally occurring electrical disturbances that originate within Earth’s atmosphere. Is often in the form of impulses that spread energy throughout a wide range of frequencies.

EXTERNAL NOISE Extraterrestrial noise Consists of electrical signals that originate from outside Earth’s atmosphere. 2 categories: Solar noise: is generated directly from sun’s heat. Cosmic noise: are continuously distributed throughout the galaxies.

EXTERNAL NOISE Noise that is produced by mankind. Man-made noise Noise that is produced by mankind. Predominant sources are spark- producing mechanisms such as commutators in electric motors, automobile ignition systems, ac power- generating and switching equipment. Is impulsive in nature and contains a wide range of frequencies that are propagated through space in the same manner as radio waves.

INTERNAL NOISE Electrical interference generated within a device or circuit. 3 primary kinds: Shot noise Transit time noise Thermal noise

INTERNAL NOISE Shot Noise Caused by a random arrival of carriers (holes and electrons) at the output of an electronic devices such as diode, field-effect transistor or bipolar transistor. Randomly varying & superimposed onto any signal present. Sometimes called transistor noise.

INTERNAL NOISE Transit-time noise: Any modification to a stream of carriers as they pass from the input to output of a device produces an irregular, random variation.

Thermal Noise Rapid and random movement of electrons within a conductor due to thermal agitation. Is present in all electronic components and communications systems. Is a form of additive noise, meaning that it cannot be eliminated and it increases in intensity with the number of devices in a circuit and with circuit length.

Thermal Noise Since it is dependent on temperature, it is also referred to as thermal noise. Thermal noise power is proportional to the product of bandwidth and temperature. Where PN = noise power (Watts) B = bandwidth (Hz) K = Boltzman’s constant (1.38 x 10-23 joules per kelvin) T = absolute temperature (kelvin) (room temperature = 17oC or 290K) To convert oC to kelvin, add 273oC

EXAMPLE 1 Convert the following temperatures to kelvin: 100oC, 0oC and -10oC. Solution: T = oC + 273oC T =100 oC + 273oC = 373K T = 0oC + 273oC = 273K T = -10oC + 273oC = 263K

NOISE VOLTAGE From the study of circuit theory, the relationship between source resistor and matched load under maximum power transfer is when RN = RL . The total of noise source power is PN.

When RN = RL = R, Therefore voltage at RL is

EXAMPLE 2 For an electronic device operating at a temperature of 170C with a bandwidth of 10 kHz, determine: (a) thermal noise power in watts and dBm (b) rms noise voltage for a 100Ω internal resistance and 100Ω load resistance.

How to Quantifying the Noise? The presence of noise degrades the performance of analog and digital communication. The extent to which noise affects the performance of communication systems is measured by the output signal to noise power ratio or SNR (for analog communication systems) and probability of error (for digital communication systems).

How to Quantifying the Noise? The signal quality at the input of the receiver is characterized by the input signal to noise ratio. Because of the noise sources within the receiver, which is introduced during the filtering and amplification processes, the SNR at the output of the receiver will be lower than at the input of the receiver. This degradation in the signal quality is characterized in terms of noise equivalent bandwidth, N0, effective noise temperature, Te and noise figure,F

Noise Calculation SNR is ratio of signal power, S to noise power, N. Noise Factor, F Noise Figure, NF

Noise Calculation In Amplifier o Two types of model - Noise amplifier Model. - Noiseless amplifier model.

Analysis of Noise Amplifier Model

Analysis of Noiseless Amplifier Model

SNR0 <<< SNRi As known as Noise Factor, Noise Temperature,

Analysis of Cascade Stages Consider three two ports in cascade G3 So No G1 F2, G2, Te2 antenna pre-amplifier demodulator amplifier F1, Te1 F3, Te3 Si Ni Ti Nai1 Nai2 Nai3 S1 N1 S2 N2 Stage 1 Stage 2 Stage 3

Stage 1

Stage 2

Stage 3

Noise Factor, F

Known as the overall noise factor, FTOTAL

And we can calculate noise temperature, Te

It can also be shown that the overall noise figure, F and the effective noise temperature, Te of n networks in cascade is given by:

Transmission Loss, Attenuator Every transmission medium will produce power loss. Pout < Pin. Power loss or attenuated is given by the following equation:

Transmission Loss, Attenuator We also can calculate by using this following equation; Where ℓ = transmission medium length α = attenuated constant

EXAMPLE 3 Determine: Noise Figure for an equivalent temperature of 75 K (use 290 K for the reference temperature). Equivalent noise temperature for a Noise Figure of 6 dB.

EXAMPLE 4 For three cascaded amplifier stages, each with noise figure of 3dB and power gain of 10 dB, determine the total noise figure.

Example 5 An amplifier consists of three identical stages in tandem. Each stage having equal input and output impedances. For each stages, the power gain is 8 dB when correctly matched and the noise figure is 6dB. Calculate the overall power gain and noise figure of the amplifier.

At the end of this chapter, you should be able To differentiate the types of noise To calculate the thermal noise generated by a resistor To calculate the signal-to-noise ratio (SNR) and noise figure for an amplifier

END OF PART 2.1