1. CHAPTER 1
Part 2.1  Noise

2. 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

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

4. 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?
transmission medium
Equipments

5. 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.

6. Block Diagram of Communication System With the Existence of Noise

7. 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.

8. 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.

9. 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.

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

11. Types of NOISE

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

13. 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.

14. 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.

15. 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.

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

17. 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.

18. 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.

19. 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.

20. 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 joules per kelvin)
T = absolute temperature (kelvin) (room temperature = 17oC or 290K)
To convert oC to kelvin, add 273oC

21. 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

22. 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.

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

24. 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.

25. 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).

26. 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

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

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

29. Analysis of Noise Amplifier Model

30. Analysis of Noiseless Amplifier Model

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

32. 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 Stage Stage 3

33. Stage 1

34. Stage 2

35. Stage 3

36. Noise Factor, F

37. Known as the overall noise factor, FTOTAL

38. And we can calculate noise temperature, Te

39. 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:

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

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

42. 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.

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

44. 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.

45. 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

46. END OF PART 2.1