Noise source in the circuit

    All electrical signals except useful signals in the circuit are noise. This definition does not apply to distortion caused by non-linearity in the circuit. Although these distortions may not be what we need, as long as it is not coupled into another part of the circuit, it is not considered noise. Similarly, useful signals in some parts of the circuit can be regarded as noise if they are coupled into other parts of the circuit.

     Noise sources can be divided into three main categories:

     (1) Intrinsic noise sources, which come from random fluctuations in physical systems, such as thermal noise and shot noise;

     (2) Man-made noise sources, such as motors, switches, digital electronic equipment, radio transmitters, etc.;

     (3) Noise caused by interference in nature, such as lightning and sunspot activity.

     Interference is an undesirable result caused by noise. If a noise voltage causes a circuit to malfunction, it is a disturbance. Noise cannot be eliminated, but can only be reduced as much as possible in magnitude until it no longer causes interference.

(Huiputech)