Chapter 1 : Introduction to Electronic Communications System

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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

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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

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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

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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)

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1.2 Communication Transmission/Mode

• Half-duplex System vs Full-duplex System

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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 !

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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)

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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

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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)

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1.3.1 dB

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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.

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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)

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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

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1.3.2 dBm

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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.

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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

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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.

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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.

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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.

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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.

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1.4 Electromagnetic Frequency Spectrum

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1.4 Electromagnetic Frequency Spectrum

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1.4 Electromagnetic Frequency Spectrum

• Ex. 8 Determine the wavelength in meters for
  the following frequencies 1 kHz, 100 kHz and 10
  MHz

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1.5 Bandwidth

• Bandwidth of an information signal is the
  difference between the highest and the lowest
  frequency contained in that signal.
• Bandwidth of a communication channel is a
  difference between the highest and the lowest
  frequency that the channel will allow to pass
  through it.
• Bandwidth of a communication channel must be
  equal or greater than the bandwidth of the
  information.
• Ex voice signals contain frequencies between
  300 Hz 3000 Hz. For that a voice signal
  communication channel must have a bandwidth of
  2700 Hz or greater.

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1.6 Information Capacity

• Information capacity is a measure of how much
  information can be propagated through a
  communication system.
• It can be expressed in the function of bandwidth
  and transmission time.
• It represents the number of independent symbols
  that can be carried through a system in a given
  unit of time
• Based on Hartleys Law,
• (7)
• where I information capacity (bits per second)
• B bandwidth (Hz)
• t transmission time (seconds)

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1.6 Information Capacity

• In 1948, Claude E. Shannon published what is
  called as Shannon limit for information capacity
  defined as follow
• Based on this law, the information capacity of
  any communication channel is related to its
  bandwidth and the signal-to-noise ratio.
• The higher the signal-to-noise ratio, the better
  the performance and the higher the information
  capacity is.
• Mathematically, it is defined as,
• (8)
• or
• (9)

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1.6 Information Capacity

• where I information capacity (bits per second)
• B bandwidth (Hz)
• S/N signal to noise power ratio
  (unitless)
• Ex 9 For a standard telephone circuit with a
  signal-to-noise ratio of 1000 (30 dB) and a
  bandwidth of 2.7 kHz, determine the Shannon limit
  for information capacity.

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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

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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 earths atmosphere such as
  lightning.
• also known as static electricity.
• Extraterrestrial noise
• consists of electrical signal that originate from
  outside earths atmosphere and therefore also
  known as deep-space noise.
• 2 categories of extraterrestrial noise.
• i solar noise noise that generated directly
  from the suns 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).

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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).

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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 ºC 273º

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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)

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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

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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.

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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 !

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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.

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1.8 Noise Parameters1.8.1 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)

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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

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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.

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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.

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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)

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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 !!!

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1.9 Examples

• Ex 1 Convert the following temperatures to
  Kelvin 100º C, 0º C and -10º C.

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1.9 Examples

• Ex 2 For and electronic device operating at a
  temperature of 17º 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.

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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.

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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.

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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

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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.