Types Of Noise Sources: Thermal, Shot,
One-Over-F, And White Noise
2. Types of Noise sources:
There are several types of noise sources in electrical
circuits. However, we discuss only threee important noise
1. Thermal or Johnson Noise
2. Shot Noise
3. 1/f Noise (Also called Flicker or Pink noise)
1. Thermal Noise: This is the noise generated by thermal
agitation of electrons in a conductor.
The noise power, P, in watts, is given by P = kT D f,
Where, k is Boltzmann's constant in joules per Kelvin,
T is the conductor temperature in Kelvin, and
D f is the bandwidth in hertz.
Note that thermal noise power, per hertz, is equal throughout
the frequency spectrum, depends only on k and T. The Thermal
noise is also called Johnson's noise.
2. Shot Noise: Shot noise normally occurs when there
is a potential barrier (voltage differential). PN junction
diode is an example that has potential barrier. When the
electrons and holes cross the barrier, shot noise is produced.
For example, a diode, a transistor, and vacuum tube will
all produce Shot noise. On the other hand, a resistor normally
does not produce Shot noise since there is no potential
barrier built within a resistor. Current flowing through
a resistor will not exhibit any fluctuations. However, current
flowing through a diode produces small fluctuations. This
is due to electrons (in turn, the charge) arriving in quanta,
one electron at a time. The current flow is not continuous,
but limited by the quantum of the electron charges.