# 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 sources here.

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.