Flicker noise is a type of
electronic noiseElectronic noise is a random signal characteristic of all electronic circuits. Depending on the circuit, the noise generated by electronic devices can vary greatly. Noise can be produced by several different effects. Thermal noise and shot noise are inherent to all devices...
with a 1/
ƒ, or
pinkPink noise or 1/ƒ noise is a signal or process with a frequency spectrum such that the power spectral density is inversely proportional to the frequency. In pink noise, each octave carries an equal amount of noise power...
spectrum. It is therefore often referred to as
1/ƒ noise or
pink noisePink noise or 1/ƒ noise is a signal or process with a frequency spectrum such that the power spectral density is inversely proportional to the frequency. In pink noise, each octave carries an equal amount of noise power...
, 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
recombinationIn the solid state physics of semiconductors, carrier generation and recombination are processes by which mobile charge carriers are created and eliminated. Carrier generation and recombination processes are fundamental to the operation of many optoelectronic semiconductor devices, such as...
noise in a
transistorA transistor is a semiconductor device commonly used to amplify or switch electronic signals. A transistor is made of a solid piece of a semiconductor material, with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's...
due to base current, and so on. It is always related to a
direct currentDirect current is the undirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also be through...
.
In electronic devices, it is a low-frequency phenomenon, as the higher frequencies are overshadowed by
white noiseWhite noise is a random signal with a flat power spectral density. In other words, the signal contains equal power within a fixed bandwidth at any center frequency...
from other sources.
Flicker noise is a type of
electronic noiseElectronic noise is a random signal characteristic of all electronic circuits. Depending on the circuit, the noise generated by electronic devices can vary greatly. Noise can be produced by several different effects. Thermal noise and shot noise are inherent to all devices...
with a 1/
ƒ, or
pinkPink noise or 1/ƒ noise is a signal or process with a frequency spectrum such that the power spectral density is inversely proportional to the frequency. In pink noise, each octave carries an equal amount of noise power...
spectrum. It is therefore often referred to as
1/ƒ noise or
pink noisePink noise or 1/ƒ noise is a signal or process with a frequency spectrum such that the power spectral density is inversely proportional to the frequency. In pink noise, each octave carries an equal amount of noise power...
, 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
recombinationIn the solid state physics of semiconductors, carrier generation and recombination are processes by which mobile charge carriers are created and eliminated. Carrier generation and recombination processes are fundamental to the operation of many optoelectronic semiconductor devices, such as...
noise in a
transistorA transistor is a semiconductor device commonly used to amplify or switch electronic signals. A transistor is made of a solid piece of a semiconductor material, with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's...
due to base current, and so on. It is always related to a
direct currentDirect current is the undirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also be through...
.
In electronic devices, it is a low-frequency phenomenon, as the higher frequencies are overshadowed by
white noiseWhite noise is a random signal with a flat power spectral density. In other words, the signal contains equal power within a fixed bandwidth at any center frequency...
from other sources. In oscillators, however, the low-frequency noise is mixed up to frequencies close to the carrier which results in oscillator
phase noisePhase noise is the frequency domain representation of rapid, short-term, random fluctuations in the phase of a wave, caused by time domain instabilities . Generally speaking radio frequency engineers speak of the phase noise of an oscillator, whereas digital system engineers work with the jitter...
.
Flicker noise is often characterized by the corner frequency
ƒc between the regions dominated by each type.
MOSFETThe metal–oxide–semiconductor field-effect transistor is a device used to amplify or switch electronic signals. The basic principle of the device was first proposed by Julius Edgar Lilienfeld in 1925...
s have a higher
ƒc than
JFETThe junction gate field-effect transistor is the simplest type of field effect transistor. It can be used as an electronically-controlled switch or as a voltage-controlled resistance. Electric charge flows through a semiconducting channel between "source" and "drain" terminals...
s 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•
WLƒ), 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
DCDirect current is the undirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also be through...
, 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.
Measurement
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:
to
where
Td is the time between measurements,
and
a includes the contribution of both positive and negative frequency terms.
After some manipulation, the variance of the voltage difference is:
where
ƒh is a
brick-wall filter limiting the upper bandwidth during measurement.
Real measurements involve more complicated calculations.