4. What is Noise?
Noise is an unwanted signal which interferes with the original
message signal and corrupts the parameters of the message
signal.
It is most likely to be entered at the channel or the receiver.
5. Noise signal can be understood by taking a look at
the following example:
• Noise is some signal which has no pattern
and no constant frequency or amplitude.
• It is quite random and unpredictable.
• Measures are usually taken to reduce it,
though it can’t be completely
eliminated.
6. Effects of Noise
Noise is an inconvenient feature which affects
the system performance.
Following are the effects of noise.
1) Noise limits the operating range of the
systems.
2) Noise affects the sensitivity of receivers.
7. Types of Noise
The classification of noise is done depending on the type of the
source.
Internal Source
1. Thermal Noise
2. Semiconductor
Noise
• Shot noise
• Transit-time
noise
• Flicker noise.
External Source
1. Industrial Noise
2. Atmospheric
Noise
3. Extraterrestrial
Noise.
8. INTERNAL SORCE
This noise is produced by the receiver components whilefunctioning.
Electronic components in a receiver such as resistors, diodes, and trasistors are the
major sources of internal noise.
Examples:
1. Thermal agitation noise (Johnson noise or Electrical noise).
2. Shot noise (due to the random movement of electrons and holes).
3. Transit-time noise (during transition).
4. Flicker noise.
9. Thermal Noise
It arises due to random motion of free charge particles.
Mainly electrons in conducting media.
The intensity of random motion is proportional to
thermal (heat energy) supplied. E.g. Tempreture.
The net motion of the electrons gives rise to an electric
current to flow through the resistor causing the noise.
10. Shot Noise
It is produced due to shot effect.
It is produced in amplifyingdevices rather than in all.
It is produced because of random variation of electrons or holes
(charge carrier).
11. Transit time Noise
Another kind of noise that occurs in transistors is called transit
time noise.
If the time taken by electron from emitter to collector
becomes comparible to period of signal then the transit time
effect takes place.
This effect can be observed at very high frequency.
Due to this some carriers may diffuse back to emitter.
This gives rise to input impedance.
So minut change at input generates random fluctuations at
output.
12. Flicker Noise
It will appear at frequency is below few kilohertz.
It is also referred as 1/f noise.
It is generated because of fluctuation in current density.
This will change conductivity of material.
This will produce fluctuation in voltage and current.
The mean square value of flicker noise is directly proportional to the square
of direct current flowing Throgh the device.
F<100 kHz
