Electronic non-coupled noise names

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A lot of electronic noise comes from other things, coupled via resistance, inductance, or capacitance -- see Electronic coupled noise for that.


There are other sources of noise,many of them imperfections of electronic components, or their real-world behaviour. Some of these are detailed below (though note some have implications on coupling as well)


Thermal noise

Thermal noise, a.k.a. Johnson–Nyquist noise, refers to agitation of electrons in charge carriers that happens purely due to their temperature.


If it's not at 0 Kelvin, then it's showing some of this. It's usually insignificant - but relevant e.g. in sensors that by their nature give weak signals, so must be amplified quite a bit.

For example image sensors, and it's more noticeable shooting in low light because then this noise is close in amount to the real signal you want.

Cameras will clear their image sensors of charge just before capture to minimize any initial pixel-well charge that came from thermal (and other) noise, which works well particularly on very short exposures as less thermal noise can accumulate. It's less avoidable in e.g. long low-light exposures (though depending on the shot, not necessarily a huge problem either).


(Sometimes called dark noise, as in image sensors this leads to seeing false signal in compete darkness. This name is potentially confusing as there are other noises that are related to darkness and/or called dark)


The frequency content of thermal noise is roughly that of white noise. (verify)


Cooling the electronics can make this effect smaller relative to most other practical noise sources.

How cold it needs to be depends on various things, often largely the integration interval (how long you sample).

...and on practical details like that at some point you just make another noise source more significant and there's no point to cooling further. In most cases -25C to -50C is already a lot. More than that sometimes happens, e.g. in astronomy and other (often-stationary) scientific applications.

Cooling is impractical for e.g. handheld cameras (but does help, see e.g. some DIY astrophotography out there).

Infrared cameras want cooling when they want more precision or speed (though don't require it to work at all).



Shot noise
This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Shot noise is a result of the discrete nature of what we are sensing (photons, electrons, or such), and of statistics.


Consider a digital photo sensor, and ignore thermal noise.

The darker it is, and the shorter the exposure, the fewer photons you actually count in a pixel well, so the more that the amount of photons and the interval of their arrival matters.


So the larger the relative magnitude of the counts between similar signal in other pixels.

In part because you'll see the differences in this interval as variation between pixels.


In other words, the darker things are, the more our sensor is trying to count photons, where usually you get nice integrated average.

Not linearly - the relation is apparently apparently sqrt(intensity)(verify) - but bright scenes implying a buttload of photons per pixel well means this is no longer noticeable in e.g. outdoor photography.

Dark shot noise

Dark shot noise (or dark-current shot noise) - refers to noise that originates from current leaking from image sensor's pixels charge wells.

For example, structural flaws may mean specific rows, columns, or pixels always drain faster.


If a subset of pixels do so consistently, this can be corrected to a good degree: measuring the effective gain, and multiplying every image by that.

Note that this mainly just puts their response on the same magnitude (so this won't look like dark pixels / lines). This is good enough for photography, while in scientific use you may wish to consider the lower response may mean lower resolution

Flicker noise

Flicker noise happens when a component or circuit shows a noticeably variation in resistance (intended workings, unavoidable imperfections, etc), leading to differences in sensed current or voltage.


It is often seen as imperfections in electronics, and alongside other electronic imperfections.

It is more noticeable for DC and low frequencies.


Because the above is a vague definition, and because it has a 1/f (pink) spectrum, it is sometimes called 1/f noise -- though "1/f noise" is a wider concept because this is not the only reason for 1/f style noise.


Impulse noise, burst noise

Impulse noise, burst noise, popcorn noise, bi-stable noise, random telegraph signal are all closely related, and used as near-synonyms.


Definitions (and synonymity) vary with context.

Often, it refers to either

  • near-instant ticks in a signal, e.g. caused by certain types of signal interference
  • step-like transitions in signal levels (e.g. in semiconductors)


See also:



Salt-and-pepper noise

Also sometimes spike noise, and some causes are closely related to impulse noise.


Named for (digital) images - sparse white pixels (salt noise) and/or sparse black pixels (pepper noise), which often come from bad gain, ADC errors, or near-zero response (dead pixels).


It can groups a few more specific things (e.g. dark shot noise), and some of them can be corrected for.


Has a fat-tail distribution.(verify)

Readout noise

Readout noise - one of various imperfections in readout electronics.

Typically presented as a sum of all such noise on a chip, though often one or two are the major contributors, and then often mainly the amplification step.


Specific readout noise sources include:

  • amplifier shot noise
  • amplifier 1/f noise
  • column amplifier noise
  • pixel noise
  • Dark current - Non-uniformity rather than noise: the reproducible amount of reaction that happens in response to no input signal.
Can be dealt with decently by getting an average of many dark images (dark frame, a.k.a. zero frame, sometimes bias frames) and subtracting that from all later images.


Avalanche noise

A reference to avalance breakdown in semiconductors. The very short version is that when this starts to happen, the current flow is ragged.

http://en.wikipedia.org/wiki/Noise_(electronics)#Avalanche_noise


Sometimes used intentionally as a source of randomness, audio noise (it's pretty wideaband white noise), or even (relaxation) oscillation.

See also