Shot noise

Electrical shot noise is a form of noise which always occurs when an electric current has to overcome a potential barrier.

The shot noise is because the total current flow from the movement of individual charge carriers (electrons or holes) is composed, and crosses each charge carrier for this barrier. This happens not uniform but is a stochastic process. In sum, certain variations of current flow are also observed at the macroscopic level.

The average square noise current can be expressed by the equation

Express, where e is the elementary charge, I is the current flowing in the conductor, and the bandwidth of the measurement. The dimension of the mean square noise current is therefore [A2 ].

The size of the shot noise therefore depends on the size of the current flowing and exhibits no direct temperature dependence. It is thus distinguished from the noise in the thermal equilibrium, the Johnson - Nyquist noise. The square of the current noise power in a frequency band is independent of the frequency and proportional to the width of the frequency band for technical frequencies. Only from frequencies whose period is as short as about the transit time, the shot noise decreases with 1/f2.

Shot noise is important in electronics, communications engineering and in basic physics, since it can be used as a noise standard for the measurement of the noise of electronic components. Be used semiconductor diodes with avalanche breakdown. These noise standards are adjusted to a predetermined characteristic impedance Z and supplied with a calibration table, which indicates the noise power density as a function of the diode current. This noise source is then connected upstream of the quadrupole to be measured. Thus, the noise figure and noise temperature of the two-port network can be determined.

Shot noise in optics

The power and an ideal monochromatic radiation source is not completely constant, but has small deviations from the mean power P in. The averaged square of the change in performance can be explained by the equation

Express, where h is Planck's constant, the frequency of the radiation (of the order 1014 Hz) and the bandwidth of the measurement are. Because this noise can not be suppressed by technical measures, including the designation of shot noise limit is used.