1/F Noise: Flicker Noise Impact and Mitigation Strategies

Key Takeaways

• 1/f Noise Impact: Pink noise or flicker noise, a common electronic issue, has implications for circuits and components due to its spectral behavior and origin in fluctuations.

• Flicker Noise Dynamics: Oscillators and components experience flicker noise due to irregularities and bias currents, impacting performance and stability.

• Mitigating Noise: Engineers counter 1/f noise through compensation, feedback, chopper stabilization, and AC excitation, enhancing electronic performance.

This diagram shows where flicker noise vs. other types of noise dominates with respect to an oscillator.

In electronics, the phenomenon known as 1/f noise, or pink noise due to its spectral characteristics, is a ubiquitous presence in most components. Also known as 1/f flicker noise,  this distinctive type of electronic noise is characterized by a power spectral density inversely proportional to the frequency—hence its name. This phenomenon has profound implications for various electronic components and circuits, including radio frequency (RF) electronics oscillators, transistors, and more. Read on as we delve into 1/f flicker noise.

1/F Noise in Electronics

At its core, 1/f noise emerges due to fluctuations caused by various mechanisms, such as impurities in conductive channels or the intricate interplay of charges within transistors. It is a characteristic noise prevalent in many electronic devices and systems, frequently linked to the flow of direct current. The term "1/f noise" derives from its behavior: as frequency or offset increases, the power density of the noise diminishes, displaying a spectral profile akin to pink noise. 

Flicker noise manifests in various electronic components due to irregularities within the conduction path, coupled with noise from bias currents within transistors. The extent of its impact on overall noise is defined by the presence of a corner frequency denoted as "fC." This frequency marks the boundary between the low-frequency realm, where flicker noise predominates, and the higher-frequency domain, characterized by the uniform spectral distribution of white noise.

• MOSFETS: At low frequencies, 1/f noise can significantly degrade the performance of MOSFETs by introducing fluctuations in the threshold voltage, thereby affecting the overall device behavior. MOSFETs exhibit a notably high corner frequency (fc), potentially extending into the gigahertz range. 

• JFETs and BJTs both showcase a lower corner frequency, typically around 1 kHz. In some instances, JFETs can exhibit slightly higher corner frequencies, reaching up to several kilohertz, rendering them less suitable for applications sensitive to flicker noise.

• In thick-film and carbon-composition resistors, 1/f noise can be referred to as excess noise. Wire-wound resistors tend to possess the lowest level of flicker noise among these components.

• In general, for RF amplifiers, the presence of 1/f noise can lead to an increase in the noise figure and degrade the overall signal-to-noise ratio. For this reason, in the pursuit of achieving optimal direct current (DC) performance characterized by minimal offset drift and low initial offset, zero-drift amplifiers offer an additional advantage: the suppression of flicker noise. This attribute holds particular significance for applications operating at low frequencies.

1/F Flicker Noise in Oscillators

The presence of 1/f flicker noise influences the behavior of oscillators. Oscillators are particularly susceptible to the effects of flicker noise due to their intrinsic nature of relying on phase shifts and feedback loops. 1/f noise can lead to frequency fluctuations and phase noise, which are detrimental to applications requiring precise timing or frequency stability.

While the presence of white noise usually overshadows higher-frequency flicker noise, oscillators can intertwine low-frequency noise with higher frequencies, ultimately resulting in significant phase noise. As the frequency decreases, the prominence of flicker noise increases, creating a scenario where it dominates over other forms of noise, such as shot noise and thermal noise. Within the oscillator circuitry, this noise manifests itself as sidebands located near the carrier signal.  Simultaneously, other noise types extend outward from the carrier with a more uniform spectral distribution, albeit diminishing as the offset from the carrier grows. This interplay establishes a corner frequency (fc) that separates the regions dominated by distinct noise types. 

Minimizing 1/F Flicker Noise

Engineers and researchers have delved into strategies to reign in this noise and preserve the integrity of electronic signals. One major method involves feedback mechanisms and compensation techniques, which are pivotal in suppressing the noise's impact. Techniques such as phase-locked loops (PLLs) and temperature compensation can be employed to restore stability and accuracy to oscillators that might otherwise succumb to the high flicker noise.

Another method, chopper stabilization, often called chopping, represents a methodology employed for mitigating amplifier offset voltage. However, the significance of this technique extends beyond just offset voltage alone, as it also demonstrates effectiveness in curtailing low-frequency 1/f noise, which is predominantly present near direct current (DC). The operational principle behind chopper stabilization involves a cyclic modulation approach: Initially, the input signals undergo alternation or chopping at the input stage. Subsequently, the modulated signals are once again subjected to chopping at the output stage. This process can be likened to modulation by utilizing a square wave waveform.

Another final method for cases where a sensor necessitates an excitation signal, the option to eradicate 1/f noise from the sensor, becomes viable through the implementation of AC excitation. The mechanism of AC excitation hinges on oscillating the source of excitation applied to the sensor, resulting in the generation of a square wave output from the sensor. This output is then subjected to subtraction across each phase of the excitation. Noteworthy benefits emanate from this strategy: not only does it enable the elimination of the sensor's 1/f noise, but it also addresses concerns like offset drift within the sensor and the undesirable influence of parasitic thermocouple effects.

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