The current noise is a noise that appears when flow of electric current is formed. It acts like an interference on the useful signal and thus deteriorates the quality of the signal. In other words: the signal-to-noise ratio ( English signal-to-noise ratio , SNR or S / N) is reduced.
The term current noise is mostly used in a very general way. As a collective term, it summarizes a large number of effects that can cause noise when the electrical current flows. Less often, the term is equated with a single cause, shot noise .
Noise in the flow of electricity
Most of the noise sources listed here are also explained using the example of the electron tube in the Wikipedia article on the electron tube.
- Power distribution noise
- The different speeds of the individual charge carriers cause noise. This effect occurs, among other things, in electron tubes .
- is a form of noise that was first observed when electrons were emitted from hot cathodes . The sparkling noise is explained by processes on the surface of the cathode as a result of diffusion and charge reversal of foreign atoms. The partially visible "sparkle" (English: flicker ) gave this type of noise its name.
- Shot noise
- (Also Schottky noise or simply current noise) The shot noise always occurs when an electrical current has to overcome a potential barrier. Every single charge carrier ( electrons or holes ) involved in the overall flow of current has to cross this barrier for itself. This does not happen evenly, but is a statistical process. In sum, certain fluctuations in the current flow can also be observed on a macroscopic level, which cause the noise.
- Influenza noise
- In the case of electron tubes , there are mainly influential processes at frequencies above 100 MHz , which are the cause of this noise.
- Heat noise
- (also: thermal noise, resistance noise, Nyquist noise, Johnson noise or Johnson-Nyquist noise) is largely white noise that arises from the thermal movement of charge carriers in electrical circuits . With unloaded ohmic resistors, heat noise expresses itself as thermal resistance noise , often simply called resistance noise. The thermal motion of the conduction electrons generated at the terminals of the dipole to the noise power and the noise voltage.
- Popcorn noise
- or bursts of noise. The cause of this noise is metallic impurities in the semiconductor. These can result in sudden changes in the DC parameters and thus trigger low-frequency pulses.
- Generational recombination noise
- In semiconductors (n- and p-conducting silicon monocrystals), the current noise that occurs can be interpreted as generation recombination noise. This noise occurs below the characteristic frequency as white noise and above as 1 / f² noise . Where is the relaxation time of the system.
Noise in the processing, transmission and conversion of signals
There are also various sources of noise when processing, transforming or converting electrical signals. These are usually not referred to as current noise , but should still be mentioned here for an overview:
- Quantization noise
- When an analog signal is digitized by an analog-digital converter , quantization noise occurs. The quantization into a finite number of quantization levels , which is practically always carried out in bits , results in a reduced resolution and quantization errors . These errors act like noise on the signal and are therefore called quantization noise . With an ideal analog-to-digital converter, a signal-to-noise ratio of around 6 dB per bit is possible.
- Tape noise
- arises from the magnetic tape recording of audio and video signals.
- Antenna noise
- arises from all types of undesired electromagnetic radiation in the transmission band, such as ignition and switching sparks and thunderstorms.
- Comfort noise
- ( English comfort noise ) is an artificially generated noise in the context of digital signal processing , which is used in the digital transmission of human speech to fill in pauses in speech.
- Horst Schwetlick: PC measurement technology. Basics and applications of computer-aided measurement technology ( Vieweg's technical books on technology ). Vieweg Verlag, Braunschweig u. a. 1997, ISBN 3-528-04948-4 , 5th chapter (PDF)
- Manfred Seifart: Analog circuits. 6th, revised edition. Verlag Technik, Berlin 2003, ISBN 3-341-01298-2 .
- Martin Werner: Communication technology. Analog and digital processes with modern applications ( study technology ). Vieweg, Wiesbaden 2006, ISBN 3-528-04126-9 , in particular the chapter on noise in communication systems , excerpt from the text .
- Horst Schwetlick: PC measurement technology - basics and applications of computer-aided measurement technology. 1997, Chapter 5, see literature
- Rudolf Müller: Rauschen (= semiconductor electronics . Volume 15 ). 2nd, revised and expanded edition. Springer, Berlin a. a. 1989, ISBN 3-540-51145-8 (Chapters 4. and 5).
- E. Grobe, K. Seiler: Current noise in silicon. In: Annals of Physics . Volume 466, No. 1, pp. 75-82, bibcode : 1963AnP ... 466 ... 75G .
- Willy Baumgartner, Hans Ulrich Thoma: To the current noise of semiconductors. In: Journal for Applied Mathematics and Physics (ZAMP). Volume 6, No. 1, January 1955, doi: 10.1007 / BF01600735 . , pp. 66-68,