Overview of flicker noise
Electronic noise known as flicker noise or 1/f noise happens naturally in almost all electronic parts. It can also result from contaminants in conductive channels, creation and recombination noise inside transistors due to base current, and other factors. Pink noise or 1/f noise are common names for this noise. All electrical devices commonly experience this noise, which has a variety of origins but is typically correlated with direct current flow. It is important in a variety of electronic fields and is important for oscillators used as RF sources.
Because the power spectral density of this noise increases with frequency, it is sometimes referred to as low-frequency noise. Below a few KHz, this noise is generally visible. The flicker noise bandwidth ranges from 10 MHz to 10 Hz.
Figure 1: The relationship between noise voltage and frequency
Flicker noise in oscillators
Flicker noise is inversely proportional to frequency, or 1/f, and in many applications, such as RF oscillators, there are parts where flicker noise, or 1/f noise, dominates, and other regions where white noise from sources like shot noise and thermal noise, or both, dominate. Within the oscillator the flicker noise expresses itself as sidebands that are near to the carrier, the other kinds of noise stretching away from the carrier with a smoother spectrum, however fading the larger the offset from the carrier.
As a result, there is a corner frequency, fc, between the regions where the various types of noise predominate. It is typically discovered that the noise outside of the region where flicker noise predominates is phase noise for a system like an oscillator. As the offset from the carrier increases, this decays until flat white noise takes over.
MOSFETs have a greater fc (which can reach GHz levels) than JFETs or bipolar transistors, whose fc is typically below 2 kHz. When building RF oscillators, flicker noise, or 1/f noise, is a crucial type of noise. Although it is frequently disregarded, its influence can be reduced by selecting the right gadget.
Figure 2: Flicker noise in ocillators
Flicker Noise in Semiconductor
The nature of semiconductor noise and how it is specified in semiconductor devices are covered in the section that follows. Since the origin of each semiconductor noise source is a random process, the noise's instantaneous amplitude is unpredictable. The distribution of the amplitude is Gaussian (normal).
Figure 3: Flicker Noise in Semiconductor
Remember that the RMS value of noise (Vn) equals the standard deviation (σ) of the noise distribution. A random noise source's RMS and peak voltages have the following relationship: VnP-P = 6.6 VnRMS. The crest factor of any signal is the ratio of peak-to-peak to RMS voltage (VnP-P/VnRMS). Because a Gaussian noise source statistically delivers peak-to-peak voltages that are 6.6 times the RMS voltage or higher 0.10% of the time, the crest factor in Equation 1 is 6.6. The likelihood of surpassing 3.3s is 0.001 in this shaded area under the noise voltage density curve in Figure 2. It's crucial to keep in mind that while random signals (like noise) multiply geometrically in a root sum square (RSS) way, associated signals add linearly.
Flicker Noise in op Amp
Since flicker noise occurs in addition to the thermal noise present in carbon composition resistors, it is frequently referred to as excess noise there. In varied degrees, other resistor types also show flicker noise, with wire coiled having the least. The type of resistor used will not impact the noise in the circuit because flicker noise is proportional to the DC current in the device, thus if the current is kept low enough, thermal noise will predominate. Scaling up resistors to minimize power consumption in an op amp circuit may result in a reduction in 1/f noise at the expense of an increase in thermal noise. Below is the formula to calculate the flicker noise:
Figure 4: Flick noise formula
Where Ke and Ki are proportionality constants (volts or amps) representing En and In at 1 Hz. fMAX and fMIN are the minimum and maximum frequencies in hertz.
How to eliminate the flicker noise in op Amp
What is the best way to deal with this loud, low-frequency noise? With the limited bandwidth, it is almost impossible to try and filter out this noise without changing the important signal. There is yet some hope, though. Although an amplifier's inherent 1/f noise is beyond the control of a system designer, this noise source can be reduced by choosing the right amplifier for the job. The best option is a zero-drift amplifier if 1/f noise is a major problem.
Figure 5: zero-drift op amp chart
Any amplifier that uses a constantly self-correcting architecture is referred to as "zero-drift" in the industry, regardless of whether it uses an auto-zero topology, a chopper-stabilized topology, or a combination of the two. No matter the specific architecture used, the objective of zero-drift amplifiers is to reduce offset and offset drift. Other dc features, such common-mode and power supply rejection, are also significantly enhanced during the procedure. The fact that the 1/f noise is eliminated during the offset correction procedure is another significant advantage of these self-correcting designs. This noise source occurs at the input and is relatively slow moving, hence it looks to be a component of the amplifiers offset and gets adjusted accordingly.
The working mechanism of flicker noise
By raising the overall noise level above the thermal noise level, which exists in all resistors, flicker noise is produced. In contrast, wire-wound resistors have the least amount of flicker noise. This noise is merely present in thick-film and carbon-composition resistors, where it is referred to as surplus noise. Charge carriers that are sporadically trapped and released between the interfaces of two materials may be the source of this noise. Because instrumentation amplifiers use semiconductors to record electrical signals, this phenomena is common in those materials.
This noise is merely inversely proportional to the frequency. There are various areas in many applications, such as RF oscillators, where noise predominates, and other areas where white noise from sources like shot noise & thermal noise predominates. A correctly constructed system is typically dominated by this low-frequency noise.
Equation of flicker noise
Simply put, nearly all electronic components produce flicker noise. In light of this, the noise is discussed in respect to semiconductor devices, notably MOSFET devices. The formula for this noise is S(f) = K/f.
Thermal Noise vs. Flicker Noise
|
Thermal Noise
|
Flicker Noise
|
|
In order to use SAR data both quantitatively and qualitatively, thermal noise must be eliminated by normalizing the backscatter signal throughout the whole SAR image.
|
Several methods, like ac excitation and chopping, can be used to reduce this noise.
|
|
The lower parasitic resistance components will result in a reduction in the intensity of thermal noise.
|
Wherever the offset voltage of the amplifier is reduced, this noise intensity will be reduced using a chopper or chopper stabilization approach.
|
|
Anytime current passes through a resistor, thermal noise results.
|
Semiconductors used in instrumentation amplifiers to record various electrical signals typically experience this noise.
|
|
Johnson noise, Nyquist noise, and Johnson-Nyquist noise are further names for this sound.
|
1/f noise is another name for this noise.
|
|
Thermal noise is the noise caused by the equilibrium thermal agitation of the electrons in an electrical conductor.
|
Flicker noise is the sound produced by randomly trapped and released charge carriers at the interfaces of two materials.
|
Pros of the flicker noise
- As the noise is low frequency, it will become quieter if the frequency increases.
- It is an innate noise present in semiconductor devices that is caused by their physics and manufacturing process.
- The effects are typically seen in electrical components at low frequencies.
Cons of flicker noise
- Performance can be hampered by this noise in any precision DC signal chain.
- In all varieties of resistors, the overall noise level can be raised above the thermal noise level.
- It is frequency dependant.
Applications of flicker noise
- Certain passive devices and all active electronic components contain this noise.
- This phenomena typically happens in semiconductors, which are primarily used to store electrical signals in instrumentation amplifiers.
- The amplifying capabilities of the device are limited by this noise in BJTs.
- In resistors made of carbon, this noise is present.
- This noise typically appears in active gadgets because the charge conveys unpredictable behavior.
Flicker Noise FAQ
Flicker noise is measured in what ways?
Similar to other types of noise measurement, flicker noise in current or voltage can be measured. The sampling spectrum analyzer instrument extracts a discrete sample from the noise and uses the FFT method to produce the Fourier transform. Low frequencies are beyond the capability of these sensors to accurately measure this noise. Thus, sampling equipment is wideband and has a high noise level. They can reduce the noise by averaging many sample traces. Due to its narrow-band acquisition, conventional-type spectrum analyzer equipment nonetheless have a higher SNR.
What should I do to stop the flickering noise?
By a chopper stabilization technique that lowers the amplifier's offset voltage, this noise can be effectively eliminated.
Flicker Noise: Why Is It Pink?
Pink noise, which has a spectral power density reduction of 3 dB per octave, is also known as flicker noise. As a result, the frequency has an inverse relationship with the pink noise band power. Lower power is produced at higher frequencies.
Why is flickering called pink noise?
One of the most frequently seen signals in biological systems is pink noise. The term originates from the pink appearance of visible light with this power range. White noise, on the other hand, has an equal strength throughout all frequency ranges.
How is flicker noise measured?
Flicker noise is proportional to the inverse of the frequency, i.e. 1/f and in many applications such as within RF oscillators there are sections in which the flicker noise, 1/f noise dominates and other regions where the white noise from sources such as shot noise and thermal noise dominate.