Flicker Noise : Working, Eliminating, Differences & Its Applications

There are various noise sources in an op-amp (operational amplifier) but the most mysterious noise source is flicker noise. This is caused by irregularities within the conduction lane & noise because of the bias currents in the transistors. This noise enhances inversely through frequency, thus it is frequently called 1/f noise. This noise is present still at higher frequencies; however other noise sources in the op-amp begin to control, opposing the 1/f noise effects. This noise will affect all electronics like operational amplifiers but, this noise source does not have limitations within low-frequency data acquisition systems. In order to provide the best dc performance like low offset drift & low initial offset, zero-drift amplifiers also have the added benefit to eliminate flicker noise, which is very critical for low-frequency applications. This article discusses an overview of flicker noise–working and its applications.

What is Flicker Noise/Flicker Noise Definition?

Flicker noise or 1/f noise is a type of electronic noise that simply occurs in nearly all electronic devices & can come with various other effects like impurities within a conductive channel, generation & recombination noise within a transistor because of base current. This noise is frequently called pink noise or 1/f noise. This noise mainly occurs in all electronic devices & it has different causes although these are generally related to the direct current flow. It is significant in many electronic fields & it is significant in oscillators utilized as RF sources.

This noise is also known as low-frequency noise because the power spectral density of this noise will be increased when the frequency is increased. This noise can be observed normally at below a few KHz. The flicker noise bandwidth ranges from 10 MHz to 10 Hz.

Flicker Noise Equation

Flicker noise simply occurs in almost all electronic components. So this noise is mentioned in relation to semiconductor devices like transistors & particularly MOSFET devices. This noise can be expressed as

S(f) = K/f

Flicker Noise Working Principle

Flicker noise works by increasing the overall noise level above the thermal noise level, which is present in all resistors. This noise is simply found in thick-film & carbon-composition resistors, wherever it is known as excess noise, In contrast, wire-wound resistors have the least amount of flicker noise.

This noise can be caused by charge carriers that are trapped & released randomly between the interfaces of two materials. Thus this phenomenon occurs normally in semiconductors that are utilized in instrumentation amplifiers for recording electrical signals.

This noise is simply proportional to the opposite of the frequency. In many applications like RF oscillators, there are many regions where the noise dominates & other regions wherever the white noise from sources like shot noise & thermal noise dominate. Generally, this noise at low frequencies dominates a properly designed system.

Eliminating 1/F Noise

Generally, the chopping or Chopper stabilization technique is used for reducing the offset voltage of the amplifier. But, since flicker noise is near DC low-frequency noise, then it is also reduced efficiently by using this technique. This technique simply works by chopping or alternating the i/p signals at the i/p stage & after that again chopping the signals at the o/p stage. So this is equal to modulation with a square wave.

In the above ADA4522 block diagram, the i/p signal can be simply modulated to the chopping frequency at the CHOP_IN stage. The i/p signal at the CHOP_OUT stage is synchronously demodulated back to its initial frequency & at the same time, the flicker noise and offset of the amplifier i/p stage are simply modulated to the chopping frequency.

In addition to decreasing the original offset voltage, the change within offset and common-mode voltage are decreased, which provides very good DC linearity & a high CMRR (common-mode rejection ratio). Chopping also decreases the offset voltage drift and temperature, due to this reason, the amplifier that uses chopping are frequently called zero-drift amplifiers. Here, one main thing we need to consider that is, the zero-drift amplifiers remove the flicker noise of the amplifier only. Any flicker noise from various sources like the sensor will pass through unchanged.

The trade-off used for chopping is that it set ups switching artifacts into the output & enhances the input bias current. On the amplifier output, the ripple & Glitches are visible once viewed on an oscilloscope & spikes of noise are visible in the spectral density of noise when viewed with a spectrum analyzer. From analog devices, the newest zero-drift amplifiers like the ADA4522 zero-drift amplifier family utilize a patented offset & a ripple correction loop circuit to reduce switching artifacts.

Chopping is also used for ADCs & instrumentation amplifiers. Chopping is used to eliminate this noise in different devices like the AD8237 true rail-to-rail, AD7124-4 low noise & low power, zero-drift instrumentation amplifier, 24-bit Σ-Δ ADC, 32-bit Σ-Δ ADC, AD7177-2 ultralow noise, etc.

One main drawback of using square wave modulation is that these waves have various harmonics. So, noise at every harmonic will be demodulated to dc back. Instead of this, if we use sine wave modulation, then this is much less vulnerable to noise & can improve extremely small signals in the large noise otherwise interference presence. So this approach is used through lock-in amplifiers.

Difference between Thermal Noise and Flicker Noise

The difference between thermal noise and flicker noise is discussed below.

What is Flicker Noise in MOSFET?

MOSFETs have a high cut-off frequency (fc) like the GHz range whereas BJTs & JFETs have a lower cut-off frequency like 1 kHz. Generally, JFETs at low frequencies exhibit more noise as compared to BJTs & they can have high ‘fc’ like several kHz and are not preferred for flicker noise.

Advantages and Disadvantages

The flicker noise advantages include the following.

• It is a low-frequency noise so, if the frequency enhances then this noise will be decreased.
• It is an inherent noise within semiconductor devices related to the manufacturing procedure & physics of the devices.
• The effects are observed usually at low frequencies within electronic components.

The flicker noise disadvantages include the following.

• In any precision DC signal chain, this noise can limit performance.
• The overall noise level can be increased over the thermal noise level in all types of resistors.
• It is frequency dependent.

Applications

The applications of flicker noise include the following.

• This noise is found in some passive devices & all active electronic components.
• This phenomenon normally occurs within semiconductors that are mainly utilized to record electrical signals in instrumentation amplifiers.
• This noise in BJTs determines the amplifying limitations of the device.
• This noise occurs in carbon composition resistors.
• Generally, this noise occurs in active devices because the charge carries random behavior.

Q). Why is Flicker Noise Considered Pink?

Pink noise is also called flicker noise because its spectral power density reduces by 3 dB per octave. So, the pink noise band power is inversely proportional to the frequency. When the frequency is higher, then the power is lower.

Q), How do I get rid of Flickering Noise?

This noise can be efficiently reduced through a chopper stabilization technique where the offset voltage of the amplifier is decreased.

Q). How is Flicker Noise Measured?

The flicker noise measurement in current or voltage can be done similarly to other kinds of noise measurement. The sampling spectrum analyzer instrument takes a finite-time sample from the noise & calculates the Fourier transform through the FFT algorithm. These instruments do not work at low frequencies to completely measure this noise. So, sampling instruments are broadband & have high noise. These can decrease the noise by using multiple sample traces & averaging them. Conventional-type spectrum analyzer instruments still have superior SNR because of their narrow-band acquisition.

Thus, this is an overview of flicker noise – working with applications. The characteristics of flicker noise are; this noise increases when the frequency reduces, this noise is associated with a DC current within electronic devices and it includes the same power content in every octave. Here is a question for you, what is white noise?