Flicker noise

Flicker noise is a type of electronic noise with a 1/f, or pink spectrum. 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 results from a variety of effects, such as impurities in a conductive channel, generation and recombination noise in a transistor due to base current, and so on. It is always related to a direct current.

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

Flicker noise is often characterized by the corner frequency $f\_mathrm\{c\}$ between the regions dominated by each type. MOSFETs have a higher $f\_mathrm\{c\}$ than JFETs or bipolar transistors which is usually below 2 kHz for the latter.

The flicker noise voltage power in MOSFET can be expressed by K/(Cox*W*L*f), where K is the process-dependent constant, W and L are channel width and length respectively.

Flicker noise is found in carbon composition resistors, where it is referred to as excess noise, since it increases the overall noise level above the thermal noise level, which is present in all resistors. In contrast, wire-wound resistors have the least amount of flicker noise. Since flicker noise is related to the level of DC, if the current is kept low, thermal noise will be the predominant effect in the resistor, and the type of resistor used will not affect noise levels.

For measurements the interest is in the "drift" of a variable with respect to a measurement at a previous time. This is calculated by applying the signal time differencing:

$1-e^\{-Tdcdot\; s\}$

to $frac\{a\}\{f\}$

Where $Td$ is the time between measurements, $s=icdot2pi\; f$, and $a$ includes the contribution of both positive and negative frequency terms.

After some manipulation, the variance of the voltage difference is:

$2aint\_\{0\}^\{f\_\{h\}\}frac\{1-cos(Tdcdot2pi\; f)\}\{f\}df=-2acdot\; Cin(Tdcdot2pi\; f\_\{h\})$

Where $f\_\{h\}$ is a brick wall filter limiting the upper bandwidth during measurement.

 Real measurements involve more complicated calculations.

See also

• Aldert van der Ziel
• Noise (physics)
• Electronic noise

References

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• Rane Pro Audio Reference definition of "flicker noise"
• Noise Tutorial