Page "Shot noise" Paragraph 11

Shot noise in electronic circuits consists of random fluctuations of the electric current in a DC current which originate due to fact that current actually consists of a flow of discrete charges ( electrons ).

Because the electron has such a tiny charge, however, shot noise is of relative insignificance in many ( but not all ) cases of electrical conduction.

For instance 1 ampere of current consists of about electrons per second ; even though this number will randomly vary by several billion in any given second, such a fluctuation is minuscule compared to the current itself.

In addition, shot noise is often less significant as compared with two other noise sources in electronic circuits, flicker noise and Johnson – Nyquist noise.

However, shot noise is temperature and frequency independent, in contrast to Johnson – Nyquist noise, proportional to temperature, and flicker noise, with the spectral density decreasing with the frequency.

Therefore at high frequencies and low temperatures shot noise may become the dominant source of noise.