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Chapter 1 : Introduction to Electronic Communications System

1.1 Basic Communication Model. Basic communication models shows the communication flows between 2 points.Source

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Chapter 1 : Introduction to Electronic Communications System

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    1. Chapter 1 : Introduction to Electronic Communications System Main purpose of an electronic communications system is to transfer information from one place to another. Electronic communications can be viewed as the transmission, reception and processing of information between two or more locations using electronic circuit/device. In this chapter, we will cover Communication models Communication transmission modes Power measurement in electronics communication Electromagnetic frequency spectrum Communication bandwidth Information capacity BENG 2413 Communication Principles Faculty of Electrical Engineering 1

    2. 1.1 Basic Communication Model Basic communication models shows the communication flows between 2 points. Source – sender of the information Sink – receiver that receive the information Channel – transmission path/medium of the information between the source and sink BENG 2413 Communication Principles Faculty of Electrical Engineering 2

    3. 1.1 Basic Communication Model Communication system model Transmission channel – physical link between the communicating parties Modulator – transform the source signal so that it is physically suitable for the transmission channel Transmitter – introduce the modulated signal into the channel (also act as amplifier) Receiver – Detect the signal on the channel and amplify it (due to the attenuation) Demodulator – Get the source signal (original) from the received signal and pass it to the recipient BENG 2413 Communication Principles Faculty of Electrical Engineering 3

    4. 1.2 Communication / Transmission Mode Communication system can be designed for transmitting information in one or both direction. Generally, the mode of communication can be divided into 3 types : Simplex System : the system capable of sending information in one direction only where only the sender can send the information and only the recipient can receive the information. (e.g. TV & radio broadcasting) Half-duplex System : the system capable to carry information in both direction, but only one direction is allowed at a time. The sender transmits to the intended receiver, and then reverse their roles. (e.g. walkie-talkie, 2-way intercom) Full-duplex System : Information can be carried in both direction at the same time. The 2 directions of information travel are independent of each other. (e.g. ordinary/mobile phone systems, computer systems) BENG 2413 Communication Principles Faculty of Electrical Engineering 4

    5. 1.2 Communication Transmission/Mode Half-duplex System vs Full-duplex System BENG 2413 Communication Principles Faculty of Electrical Engineering 5

    6. 1.3 Power Measurement (dB, dBm & Bel) Magnitudes of communication signals span a very wide range causing a drawbacks as follow : Extremely large scale (graph/drawing) Hard calculation (too big vs too small numbers) Prone to errors (e.g. 0.0001 vs 0.00001) Hard to compare the signals As a solution, logarithmic scale is used ! BENG 2413 Communication Principles Faculty of Electrical Engineering 6

    7. 1.3.1 Decibel (dB) Used to measure the ratio between 2 values – value to be measured relative to a reference value In the electronic communication field, decibel is normally used to define the power ratios between 2 signals To express relative gain and lose of the electronic device/circuit Describing relationship between signal and noise In the common usage, it also used to express the ratios of voltage and current If 2 powers are expressed in the same units (e.g. watt, miliwatt), their ratio is a dimensionless quantity that can be expressed in decibel form as follow (1) (2) BENG 2413 Communication Principles Faculty of Electrical Engineering 7

    8. 1.3.1 Decibel (dB) Where P1 : power level 1 (watts) P2 : power level 2 (watts) the dB value is for the power of P1 with respect to the reference power P2 the dB value shows the difference in dB between power P1 and P2 BENG 2413 Communication Principles Faculty of Electrical Engineering 8

    9. 1.3.1 Decibel (dB) In the case to measure the power gain or loss of any electronic circuit or device, equation (1) can be written as follow (2) where Ap(dB) : power gain (unit in dB) of Pout with respect to Pin Pout : output power level (watts) Pin : input power level (watts) Pout/Pin : absolute power gain (unitless) Positive (+) dB value indicates the output power is greater than the input power, which indicates power gain or amplification Negative (-) dB value indicates the output power is less that the input power which indicates power loss or attenuation If Pout = Pin, the absolute power gain is 1, which means dB power gain is 0 (referred as unity power gain) BENG 2413 Communication Principles Faculty of Electrical Engineering 9

    10. 1.3.1 dB BENG 2413 Communication Principles Faculty of Electrical Engineering 10

    11. 1.3.1 dB Ex 1 : Convert the absolute power ratio of 200 to a power gain in dB. Ex 2 : Convert a power gain Ap = 30 dB to an absolute power ratio. BENG 2413 Communication Principles Faculty of Electrical Engineering 11

    12. 1.3.1 dB Ex 3 : Expressing power gain in term of voltage ratio From (3) Substituting (3) into (2), i.e. (3-1) Voltage Gain (3-2) BENG 2413 Communication Principles Faculty of Electrical Engineering 12

    13. 1.3.2 dBm A dBm is a unit of measurement used to indicate the ratio of power level with respect to a fixed reference level. With dBm, the reference level is 1 mW (miliwatts). dBm unit can be expressed as follow (4) Ex 4 : Convert a power level of 200 mW to dBm Ex 5 : Convert a power level of 30 dBm to an absolute power BENG 2413 Communication Principles Faculty of Electrical Engineering 13

    14. 1.3.2 dBm BENG 2413 Communication Principles Faculty of Electrical Engineering 14

    15. 1.3.3 Bel A Bel is one-tenth of a decibel (5) The Decibel unit was originated from the Bel unit, in honor of Alexander Graham Bell. Bel unit compressed absolute ratios of 0.00000001 to 100000000 to a ridiculously low range of only 16 Bel (-8 Bel to + 8 Bel). Difficult to relate Bel unit to true magnitudes of large ratios and impossible to express small differences with any accuracy. To overcome this, Bel was simply multiplied by 10, creating a decibel. BENG 2413 Communication Principles Faculty of Electrical Engineering 15

    16. 1.3.4 Power levels, Gains and Losses When power levels are given in watts and power gains are given as absolute values, the output power is determined by multiplying the input power with the power gains. Ex 6 : Given a 3 stages system comprised of two amplifiers and filter. The input power Pin = 0.1 mW. The absolute power gains are AP1 = 100, AP2 = 40 and AP3 = 0.25. Determine a) the input power in dBm b) output power (Pout) in watts and dBm c) the dB gain of each of the 3 stages d) the overall gain in dB BENG 2413 Communication Principles Faculty of Electrical Engineering 16

    17. 1.3.4 Power levels, Gains and Losses Ex 7 : For a 3-stages system with an input power Pin = -20 dBm and the power gains of the 3-stages as AP1 = 13 dB, AP2 = 16 dB and AP3 = -6 dB, determine the output power (Pout) in dBm and watts. BENG 2413 Communication Principles Faculty of Electrical Engineering 17

    18. 1.4 Electromagnetic Frequency Spectrum Communicating the information between two or more location is done by converting the original information into electromagnetic energy and then transmitting it to the receiver where it is converted back to its original form The electromagnetic energy is distributed throughout infinite range of frequencies The total electromagnetic frequency spectrum with the approximate locations of various services is shown below. BENG 2413 Communication Principles Faculty of Electrical Engineering 18

    19. 1.4 Electromagnetic Frequency Spectrum The spectrum is divided into bands, with each band having a different name and boundary. The radio frequency band (30Hz ~300GHz) is divided into narrower band as follow. BENG 2413 Communication Principles Faculty of Electrical Engineering 19

    20. 1.4 Electromagnetic Frequency Spectrum Wavelength : is the length that one cycle of electromagnetic wave occupies in space. It is inversely proportional to the frequency of the wave and directly proportional to the velocity of propagation. Wavelength can be defined as follow, (6) where ?= wavelength (m), c = velocity of light (3 x 108 m/s), f = frequency (Hz) Total electromagnetic wavelength spectrum is shown below. BENG 2413 Communication Principles Faculty of Electrical Engineering 20

    21. 1.4 Electromagnetic Frequency Spectrum BENG 2413 Communication Principles Faculty of Electrical Engineering 21

    22. 1.4 Electromagnetic Frequency Spectrum BENG 2413 Communication Principles Faculty of Electrical Engineering 22

    23. 1.4 Electromagnetic Frequency Spectrum BENG 2413 Communication Principles Faculty of Electrical Engineering 23

    24. 1.5 Bandwidth BENG 2413 Communication Principles Faculty of Electrical Engineering 24

    25. 1.6 Information Capacity BENG 2413 Communication Principles Faculty of Electrical Engineering 25

    26. 1.6 Information Capacity BENG 2413 Communication Principles Faculty of Electrical Engineering 26

    27. 1.6 Information Capacity BENG 2413 Communication Principles Faculty of Electrical Engineering 27

    28. 1.7 Noise – Representation, types & source Definition – any undesirable electrical energy that falls within the passband of the signal. Effect of noise on the electrical signal : 2 general categories of noise : Correlated noise – noise that exists only when a signal is present. Uncorrelated noise – noise that presents all the time whether there is a signal or not BENG 2413 Communication Principles Faculty of Electrical Engineering 28

    29. 1.7.1 Uncorrelated noise 2 general categories of uncorrelated noise : 1. External noise – noise that generated outside the device or circuit. Atmospheric noise naturally occurring electrical disturbances that originate within earth’s atmosphere such as lightning. also known as static electricity. Extraterrestrial noise consists of electrical signal that originate from outside earth’s atmosphere and therefore also known as deep-space noise. 2 categories of extraterrestrial noise. i – solar noise – noise that generated directly from the sun’s heat. ii – cosmic noise / black-body noise – noise that is distributed throughout the galaxies. Man-made noise - noise that is produced by mankind. - source : spark-producing mechanism (commutators in electrical motors, automobile ignition systems, ac power generating/switching equipment, fluorescent lights). BENG 2413 Communication Principles Faculty of Electrical Engineering 29

    30. 1.7.1 Uncorrelated noise 2 general categories of uncorrelated noise : 2. Internal noise – noise that generated within the device or circuit. Shot noise caused by the random arrival of carriers (holes and electrons) at the output element of an electronic device. shot noise is randomly varying and is superimposed onto any signal present. Transit-time noise irregular, random variation due to any modification to a stream of carriers as they pass from the input to the output of a device. this noise become noticeable when the time delay takes for a carrier to propagate through a device is excessive. thermal / random noise - noise that is produced by mankind. - source : spark-producing mechanism (commutators in electrical motors, automobile ignition systems, ac power generating/switching equipment, fluorescent lights). BENG 2413 Communication Principles Faculty of Electrical Engineering 30

    31. 1.7.1 Uncorrelated noise 2 general categories of uncorrelated noise : 2. Internal noise – noise that generated within the device or circuit. Thermal / random noise associated with the rapid and random movement of electrons within a conductor due to thermal agitation. also known as Brownian noise, Johnson noise and white noise. uniformly distributed across the entire electromagnetic spectrum. a form of additive noise, meaning that it cannot be eliminated, and it increase in intensity with the number of devices and with circuit length. the most significant of all noise sources thermal noise power can be defined as follow : (6.1) where N : noise power (watts) B : bandwidth (Hertz) T : absolute temperature (kelvin) .......... T = şC + 273ş BENG 2413 Communication Principles Faculty of Electrical Engineering 31

    32. 1.7.1 Uncorrelated noise Thermal / random noise equivalent circuit for a thermal noise source when the internal resistance of the source R1 is in series with the rms noise voltage VN for a worst case and maximum transfer of noise power, the load resistance R is made equal to the internal resistance. Thus the noise power developed across the load resistor : (6.2) thus rms noise voltage can be define as (6.3) BENG 2413 Communication Principles Faculty of Electrical Engineering 32

    33. 1.7.2 Correlated noise a form of internal noise that is correlated to the signal and cannot be present in a circuit unless there is a signal. produced by a nonlinear amplification resulting in nonlinear distortion. there are 2 types of nonlinear distortion that create unwanted frequencies that interfere with the signal and degrade the performance : 1. Harmonic distortion occurs when unwanted harmonics of a signal are produced through nonlinear amplification. harmonics are integer multiples of the original signal. The original signal is the first harmonic (fundamental harmonic), a frequency two times the fundamental frequency is the second harmonic, three times is the third harmonic and so on. Distortion measurements : BENG 2413 Communication Principles Faculty of Electrical Engineering 33

    34. 1.7.2 Correlated noise 1. Harmonic distortion distortion measurements : - Nth harmonic distortion = ratio of the rms amplitude of Nth harmonic to the rms amplitude of the fundamental. - Total Harmonic Distortion (THD) (6.4) where all in rms value. BENG 2413 Communication Principles Faculty of Electrical Engineering 34

    35. 1.7.2 Correlated noise 2. Intermodulation distortion intermodulation distortion is the generation of unwanted sum and difference frequencies produced when two or more signals mix in a nonlinear device (cross products). unwanted ! BENG 2413 Communication Principles Faculty of Electrical Engineering 35

    36. 1.7.3 Other type of noise 1. Impulse noise characterized by high amplitude peaks of short duration (sudden burst of irregularly shaped pulses) in the total noise spectrum. common source of impulse noise : transient produced from electromechanical switches (relays and solenoids), electric motors, appliances, electric lights, power lines, poor-quality solder joints and lightning. 2. Interference electrical interference occurs when information signals from one source produces frequencies that fall outside their allocated bandwidth and interfere with information signal from another source. most occurs in the radio frequency spectrum. BENG 2413 Communication Principles Faculty of Electrical Engineering 36

    37. 1.8 Noise Parameters 1.8.1 Signal-to-noise Power Ratio signal-to-noise power ratio (S/N) is the ratio of the signal power level to the noise power level and can be expressed as (6.5) in logarithmic function (6.6) in terms of voltages and resistance (6.7) in the case Rin = Rout, (6.7) can be reduced to (6.8) BENG 2413 Communication Principles Faculty of Electrical Engineering 37

    38. 1.8.2 Noise Factor and Noise Figure Noise factor is the ratio of input signal-to-noise ratio to output signal-to-noise ratio (6.9) Noise figure is the noise factor stated in dB and is a parameter to indicate the quality of a receiver (6.10) Noise Figure in Ideal and Non-ideal Amplifiers - an electronic circuit amplifies signal and noise within its passband equally well - in the case of ideal/noiseless amplifier, the input signal and the noise are amplified equally. - meaning that, signal-to-noise ratio at input = signal-to-noise ratio at output BENG 2413 Communication Principles Faculty of Electrical Engineering 38

    39. 1.8.2 Noise Factor and Noise Figure Noise Figure in Ideal and Non-ideal Amplifiers (continue) - in reality, amplifiers are not ideal, adds internally generated noise to the waveform, reducing the overall signal-to-noise ratio. - in figure (a), the input and output S/N ratios are equal. - in figure (b), the circuits add internally generated noise Nd to the waveform, causing the output signal-to-noise ratio to be less than the input signal-to-noise ratio. BENG 2413 Communication Principles Faculty of Electrical Engineering 39

    40. 1.8.2 Noise Factor and Noise Figure Noise Figure in Ideal and Non-ideal Amplifiers (continue) - in figure (b), the circuits add internally generated noise Nd to the waveform, causing the output signal-to-noise ratio to be less than the input signal-to-noise ratio. BENG 2413 Communication Principles Faculty of Electrical Engineering 40

    41. 1.8.2 Noise Factor and Noise Figure Noise Figure in Cascaded Amplifier - when two or more amplifiers are cascaded as shown in the following figure, the total noise factor is the accumulation of the individual noise factors. - Friss’ formula is used to calculate the total noise factor of several cascade amplifiers (6.11) BENG 2413 Communication Principles Faculty of Electrical Engineering 41

    42. 1.8.2 Noise Factor and Noise Figure Noise Figure in Cascaded Amplifier (continue) - the Total Noise Figure (6.12) When using Friss’ formula, the noise figures must be converted to noise factors !!! BENG 2413 Communication Principles Faculty of Electrical Engineering 42

    43. 1.9 Examples Ex 1 : Convert the following temperatures to Kelvin : 100ş C, 0ş C and -10ş C. BENG 2413 Communication Principles Faculty of Electrical Engineering 43

    44. 1.9 Examples Ex 2 : For and electronic device operating at a temperature of 17ş C, with a bandwidth of 10 kHz, determine a. thermal noise power in watts and dBm. b. rms noise voltage for a 100 O load resisstance. BENG 2413 Communication Principles Faculty of Electrical Engineering 44

    45. 1.9 Examples Ex 3 : For an amplifier with an output signal power of 10 W and output noise power of 0.01 W, determine the signal-to-noise power ratio. BENG 2413 Communication Principles Faculty of Electrical Engineering 45

    46. 1.9 Examples Ex 4 : For an amplifier with an output signal voltage of 4V, an output noise voltage 0.005 V and an input and output resistance of 50 , determine the signal-to-noise power ratio. BENG 2413 Communication Principles Faculty of Electrical Engineering 46

    47. 1.9 Examples Ex 5 : For a non-ideal amplifier with a following parameters, determine a. input S/N ratio (dB) b. output S/N ratio (dB) c. noise factor and noise figure Input signal power = 2 x 10-10 W Input noise power = 2 x 10-18 W Power gain = 1000000 Internal noise Nd = 6 x 10-12 W BENG 2413 Communication Principles Faculty of Electrical Engineering 47

    48. 1.9 Examples Ex 6 : For 3 cascaded amplifier stages, each with a noise figures of 3 dB and power gain of 10dB, determine the total noise figure. BENG 2413 Communication Principles Faculty of Electrical Engineering 48

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