Noise refers to any undesired electrical signal present in addition to the intended signal. There are two main types of noise: man-made noise from sources like machines and natural noise from components and the atmosphere. White noise contains thermal and shot noise, while pink noise contains flicker and burst noise. The thermal noise RMS voltage and shot noise RMS current can be calculated using formulas involving temperature, resistance, bandwidth, and other factors. Signal to noise ratio and noise figure are key metrics used to represent noise in signals and systems.

2.  Any undesired electrical signal that is present in addition to the
voltage or current being processed or measured is known as noise.
 Nature of noise
◦ Man made noise
e.g. Machines, X-RAYS, Electric discharge machines, Power supplies.
◦ Natural Noise
e.g. Noise in different components, Atmospheric noise.

3.  White Noise
◦ Thermal Noise
◦ Shot Noise
 Pink Noise
◦ Flicker and Burst Noise
 Atmospheric Noise
◦ Lightening and EM radiations

4. It is also known as Johnson noise, Nyquist noise, or resistance noise.
The thermal noise RMS voltage is given by
Vrms= 4𝑘𝑇𝑅∆𝑓
Where
k = Boltzmann’s constant = 1.38 x 10-23 J/K
T = Absolute temperature (K)
R = Resistance (Ω)
Δf = Effective Noise Bandwidth

5. It is also known as Schottky noise, schrot noise or partition
noise. It is due to fluctuations present is DC current wherever it
flows. RMS shot noise current is given as
Irms= 2𝑞 𝑒 𝐼 𝐷𝐶∆𝑓
Where
qe = charge on electron
Δf = effective noise bandwidth

6.  Signal to Noise ratio is used to represent noise in a signal or
system.
 It is expressed in dBs.
 It can be defined in terms of power or voltage.
(S/N)dB= 10 log (𝑃𝑆/𝑃 𝑁)
(S/N)dB= 10 log (𝑉𝑆/𝑉𝑁)
 In case of voltage based calculations log is multiplied by 20.
why?

7.  Noise figure represents how much noise is added by the
system or some stage of the system or by the amplifier stage.
N.F = (S/N)in/(S/N)out
 In dBs we can represent it as
N.FdB = [(S/N)in]dB – [(S/N)out]dB

8.  Noise is not a symmetrical sinusoidal signal and it does not
specific peak value.
 To measure noise level in a signal, true RMS meters are
required.
 But if true RMS meters are not available, then we can measure
noise level by using AC voltmeter .
 In case of AC voltmeter, the result should be multiplied by
some correction factor to get the required result.