Flicker noise

Flicker noise is a type of electronic noise with a 1/f, or "pink", power spectral density. It is therefore often referred to as 1/f noise or pink noise, though these terms have wider definitions. It occurs in almost all electronic devices and can show up with a variety of other effects, such as impurities in a conductive channel, generation and recombination noise in a transistor due to base current, and so on.

1/f noise in current or voltage is usually related to a direct current, as resistance fluctuations are transformed to voltage or current fluctuations by Ohm's law. There is also a 1/f component in resistors with no direct current through them, likely due to temperature fluctuations modulating the resistance. This effect is not present in manganin, as it has negligible temperature coefficient of resistance.

In electronic devices, it shows up as a low-frequency phenomenon, as the higher frequencies are overshadowed by white noise from other sources. In oscillators, however, the low-frequency noise can be mixed up to frequencies close to the carrier, which results in oscillator phase noise.

Flicker noise is often characterized by the corner frequency f_c between the region dominated by the low-frequency flicker noise and the higher-frequency "flat-band" noise. MOSFETs have a higher f_c (can be in the GHz range) than JFETs or bipolar transistors, which is usually below 2 kHz for the latter.

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