Intro to Electronic Comm Part2
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Transcript of Intro to Electronic Comm Part2
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Chapter 1
Introduction to Electronic
Communication Part II
Chapter 1 : Introduction to
Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 1
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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 2
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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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 3
1.7.1 Uncorrelated noise
2 general categories of uncorrelated noise : external noise and internal 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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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 4
1.7.1 Uncorrelated noise
2. Internal noise noise that generated within the device or circuit. Three primary kinds of internal noise:
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
- it is associated with the rapid movement of electron within a conductor due to thermal disturbance
- thermal noise is present in all electronic components and communication systems.
- It is also known as white noise which uniformly distributed across the entire electromagnetic frequency spectrum
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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 5
1.7.1 Uncorrelated noise
Thermal / random noise
- associated with the rapid and random movement of electrons within a conductor due to thermal agitation (disturbance)
- 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 :
(2.1)
where N : noise power (watts)
B : bandwidth (hertz)
T : absolute temperature (kelvin) .......... T = C + 273
K : Boltzmanns proportionality constant (1.38 x 10-23 joules per kelvin)
KTBN
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Example 1.10
Find the noise power in dBm at temperature of 17oC.
The bandwidth is 1 Hz for this temperature.
Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 6
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Solution:
i. Convert the temperature unit to Kelvin
T = C + 273 = 17oC + 273 = 290oK
ii. Noise power in dBm
N(dBm) = 10 log10 (KTB /0.001)
= 10 log10 (KT/0.001) + 10 log10 B
= 10 log10 (1.38 x 10-23 * 290/0.001) + 10 log10 1
= - 174 dBm
Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 7
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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 8
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 :
(2.2)
thus rms noise voltage can be define as
(2.3)
R
V
R
VKTBN
NN
4
2/ 22
RKTBVN 4
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Example 1-11
For an electronic device operating at a temperature of
17oC with a bandwidth of 10 kHz, determine:
i. Thermal noise power in watts and dBm
ii. rms noise voltage for a 100 internal resistance and a 100 load
resistance.
Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 9
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Solution: 1-11 (continue)
i. T = C + 273 = 17oC + 273 = 290oK
N = KTB = (1.38 x 10-23 x 290 x 1 x 104) = 4 x 10-17 W
N(dBm) = 10 log10 (4 x 10-17 / 0.001) = -134 dBm
ii. rms noise voltage for a 100 internal resistance and a 100
load resistance.
VN = 4RKTB
= (4 x 100 x (4 x 10-17 )
= 0.1265 V
Chapter 1 : Introduction to Communication Systems
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Faculty of Electrical Engineering 10
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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 11
1.7.2 Correlated noise
a form of internal noise that is correlated(mutually related) 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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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 12
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)
(2.4)
where
all in rms value.
100% lfundamenta
higher
v
vTHD
2 2 4 22 43 ....higher nv v v v v
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Example 1-12
Determine
i. 2nd, 3rd and 12th harmonics for 1 kHz repetitive
wave
ii. Percent 2nd order, 3rd order and total harmonic of
distortion for a fundamental frequency with an
amplitude of 8 Vrms, a 2nd harmonic amplitude of
0.2 Vrms, and a 3rd harmonic amplitude of 0.1
Vrms.
Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 13
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Solution:
i. 2nd, 3rd and 12th harmonics for 1 kHz repetitive wave
2nd harmonic = 2 x fundamental = 2 x 1 kHz = 2 kHz
3rd harmonic = 3 x fundamental = 3 x 1 kHz = 3 kHz
12th harmonic = 12 x fundamental = 12 x 1 kHz = 12 kHz
ii. Percent 2nd order, 3rd order and total harmonic of distortion for a
fundamental frequency
a. % 2nd order = V2/V1 x 100 = 0.2/8 x 100 = 2.5%
b. % 3rd order = V2/V1 x 100 = 0.1/8 x 100 = 1.25%
c. % THD = (((0.2)2 + (0.1)2)1/2 / 8) x 100% = 2.795 %
Chapter 1 : Introduction to Communication Systems BEKC 3633 Communication Systems
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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 15
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).
Mathematically, the sum and difference frequencies are:
Cross products = mf1 nf2 (2.5)
where f1 and f2 are fundamental frequencies, where f1 > f2, and m and n are
positive integers between one and infinity.
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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
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1.7.2 Correlated noise
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Example 1-13
For a non-linear amplifier with two input frequencies,
3kHz and 8kHz, determine
i. 1st three harmonics present in the output for
each input frequency.
ii. Cross product frequencies produced for values
of m and n of 1 and 2.
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BEKC 3633 Communication Systems
Faculty of Electrical Engineering 17
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Solution: i. The first three harmonics include the two original frequencies 3kHz
and 8kHz:
- two times each of original frequencies
2 * 3kHz = 6kHz; 2 * 8kHz = 16kHz
- three times each of original frequencies
3 * 3kHz = 9kHz; 3 * 8kHz = 24kHz
ii. The cross products for values of m and n of 1 and 2 are determined
by equation (2.5)
Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 18
m n
1 1 8kHz 3kHz = 5kHz and 11kHz
1 2 8kHz 6kHz = 2 kHz and 14kHz
2 1 16kHz 3kHz = 13kHz and 19kHz
2 2 16kHz 6kHz = 10kHz and 22kHz
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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 19
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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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
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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
(2.6)
in logarithmic function
(2.7)
in terms of voltages and resistance
(2.8)
in the case Rin = Rout, (2.8) can be reduced to
(2.9)
n
s
P
P
N
S
n
s
P
PdB
N
Slog10)(
outn
ins
RV
RVdB
N
S
/
/log10)(
2
2
n
s
V
VdB
N
Slog20)(
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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 21
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 and dB.
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Solution
Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 22
100001.0
10
n
s
P
P
N
S
1. Using equation 2.6
2. Convert to dB, using equation 2.7
dBdBN
S301000log10)( 10
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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 23
1.9 Examples
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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Solution
Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 24
1. Using equation 2.8
dBV
VdB
N
S
n
s06.58
005.0
4log20log20)( 1010
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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 25
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
(2.10)
Noise figure is the noise factor stated in dB and is a parameter to indicate the
quality of a receiver
(2.11)
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
out
in
NS
NSF
)/(
)/(
out
in
NS
NSFNF
)/(
)/(log10log10
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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 26
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.
i
i
iP
iP
out
out
N
S
NA
SA
N
S
(2.12)
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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 27
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.
)/( Pdi
i
diP
iP
out
out
ANN
S
NNA
SA
N
S
(2.13)
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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 28
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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Solution:
a) Using equation 6.5
Change to dB
a) Using equation 6.12
Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 29
8
18
10
10x1000,000,10010x2
10x2
in
in
N
S
000,000,2510x8
10x200
10x6)10x2(1000000
)10x2(100000012
6
1218
10
diP
iP
out
out
NNA
SA
N
S
dBN
S
dBin
in 8010x2
10x2log10
18
10
10
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Solution:
Change to dB
Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 30
dBN
S
dBout
out 74000,000,25log10 10
c. Noise Factor:
dBNFeNoiseFigur
N
S
N
SFFactorNoise
out
out
in
in
64log10
4000,000,25
000,000,100/
10
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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 31
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
(2.14)
N
NT
AAA
F
AA
F
A
FFF
...
1...
11
2121
3
1
21
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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 32
1.8.2 Noise Factor and Noise Figure
Noise Figure in Cascaded Amplifier (continue) - the Total Noise Figure
(2.15)
When using Friss formula, the noise figures must
be converted to noise factors !!!
TT FNF log10
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Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 33
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 factor and noise figure.
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Solution
Chapter 1 : Introduction to Communication Systems
BEKC 3633 Communication Systems
Faculty of Electrical Engineering 34
21
3
1
2
1
11
AA
F
A
FFFT
11.2100
12
10
122
Total Noise Figure , NFT = 10 log10 (2.11) =3.24 dB