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NOISE
NOISE
A sound, especially one that is loud or unpleasant or that causes disturbance.
A sound, especially one that is loud or unpleasant or that causes disturbance.
CATEGORIES OF NOISE
Correlated noise: noise that exist only when a signal is present
Harmonic Distortion
INTERMODULATION DISTORTION
Uncorrelated noise: noise that present all the time whether there is a signal or not
Internal
External
EFFECT OF NOISE ON THE ELECTRICAL SIGNAL
CORRELATED NOISE
CORRELATED NOISE: HARMONIC DISTORTION
❖Harmonics are integer multiples of the original signal.
❖The original signal is the first harmonic (fundamental harmonic), a frequency 2 times the fundamental frequency is the second harmonic, 3 times the third harmonic and so on.
❖Example:
In audio system: Lower distortion means the components in a loudspeaker.
In radio communications: Lower THD means a pure signal is produced without causing interference to other electronic devices.
In power systems: Lower THD means reduction in heating core loss in motors.
❖Distortion measurements:
Nth harmonic distortion = ratio of the rms amplitude of a set of higher harmonic frequencies to the rms amplitude of the fundamental harmonic.
CORRELATED NOISE: 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 product).
❖Sum and difference frequencies are called cross products.
❖Unwanted cross product frequencies can integers with the information signals.
❖Because of the non-linearities, each signal in the set combines with the others. to generate a set of second order sum and difference products, third order products, and so on.
❖The addition of the very large combination of signals results in an output noise spectrum that is approximately flat with a frequency across a narrow band of about 4kHz for most analogue systems with many multiplexed channels.
❖Intermodulation noise differs from thermal noise in that it is a function of signal power at the nonlinear point.
HARMONIC DISTORTION VS INTERMODULATION DISTORTION
UNCORRELATED NOISE
UNCORRELATED NOISE: INTERNAL
Generated within the device or circuit.
Thermal noise.
Rapid and random movement of electrons within a conductor due to thermal agitation or excitement.
Present in all electronic components and communication systems.
Shot noise.
Caused by the random arrival of carriers (holes and electrons) at the output element of an electronic device.
Example: diode, FET or bipolar transistor.
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.
The noise becomes noticeable when the time delay takes for a carrier to propagate through a device is excessive.
UNCORRELATED NOISE: EXTERNAL
Generated outside device or circuit.
Atmospheric noise.
Originate within earth’s atmosphere such as lightning.
Also known as static electricity.
Extraterrestrial noise.
Originated from outside earth’s atmosphere.
Also known as deep-space noise.
There is 2 categories:
Solar noise: generated directly from the sun’s heat.
Cosmic noise/black-body noise: distributed throughout the galaxies.
Man-made noise.
Produced by mankind.
Most occur in the more populated metropolitan and industrial areas.
Example: spark-producing mechanisms such as commutators in electrical motors, fluorescent lights etc.
Impulse noise.
High-amplitude peaks of short duration in the total noise spectrum.
Sudden bursts of irregularly shaped pulses that generally last between a few microseconds and several milliseconds.
Common sources include transients produced from electromechanical switches.
Interference.
Most occurs in the radio frequency spectrum.
When information signals from one source produce frequencies that fall outside their allocated bandwidth, and interfere with information signals another source.
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