•
produced by a nonlinear amplification resulting in nonlinear distortion.
•
there are two 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 :
22
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.
23
100
%
l
fundamenta
higher
v
v
THD
2
4
4
3
3
2
2
....
n
higher
v
v
v
v
v
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 !
24
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, poorquality 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.
25
Noise Parameters
Signaltonoise Power Ratio
•
signaltonoise power ratio (S/N)
is the ratio of the signal power level to the
noise power level and can be expressed as
(1.1)
in logarithmic function
(1.2)
in terms of voltages and resistance
(1.2)
(6.7) can be reduced to
(1.3)
26
n
s
P
P
N
S
n
s
P
P
dB
N
S
log
10
)
(
2
2
/
(
)
10log
/
s
n
S
V
R
dB
N
V
R
n
s
V
V
dB
N
S
log
20
)
(
Noise Factor and Noise Figure
•
Noise factor
is the ratio
of
input signaltonoise ratio to
output signaltonoise
ratio
(1.4)
•
Noise figure
is the noise factor stated in dB and is a parameter to indicate the
quality of a receiver
(1.5)
•
Noise Figure in Ideal and Nonideal 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,
signaltonoise ratio at input =
signaltonoise ratio at output
27
out
in
N
S
N
S
F
)
/
(
)
/
(
out
in
N
S
N
S
F
NF
)
/
(
)
/
(
log
10
log
10
Noise Factor and Noise Figure
•
Noise Figure in Ideal and Nonideal Amplifiers (continue)
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 Spring '16
 Decibel, Nonideal Amplifiers