Flicker Noise Research Articles

Comparison of Different Linewidth Measuring Methods for Narrow Linewidth Laser

We experimentally demonstrate a fiber laser with different linewidths based on self-injection locking (SIL) and the stimulated Brillouin scattering effect. Based on the homemade fiber laser, the error origin, resolution, and applicable range of delayed self-heterodyne interferometry (DSHI), self-correlation envelope linewidth detection (SCELD) and Voigt fitting are investigated numerically and experimentally. The selection of the linewidth measuring method should meet the following conclusions: an approximately Lorentzian self-heterodyne spectrum without the pedestal and high-intensity sinusoidal jitter is a prerequisite for DSHI; the SCELD needs a suitable length of delay fiber for eliminating flicker noise and dark noise of the electrical spectrum analyzer; a non-Lorentzian self-heterodyne spectrum without a pedestal is an indispensable element for Voigt fitting. According to the experimental results, the laser Lorentzian linewidth of SIL changes from 1.7 kHz to 587 Hz under different injection powers. When the Brillouin erbium fiber laser is utilized, the Lorentzian linewidth is measured to be 60 ± 5 Hz.

Transformation in Low‐Frequency Noise Spectra in GaN High‐Electron‐Mobility Transistors in Nonequilibrium Conditions

It is known that flicker noise is the most intriguing noise component because it can be found in any type of material, object, device, or system. Despite the struggle of scientists to find a mutual model for the 1/f flicker noise law, there is still a challenge to describe the law in many cases. Herein, the studies of two‐level random telegraph signal (RTS) fluctuations analyzed for the state‐of‐the‐art high‐electron‐mobility transistors (HEMTs), fabricated based on AlGaN/GaN heterostructures, are presented. It is revealed that the shape of the fluctuations can be used to describe the formation of a spectrum with γ = 1, 2, 3. The data demonstrate that the 1/f spectrum can be obtained as a result of the interactions of the carriers in parallel channels along the length of a system. Experimentally registered RTS fluctuations have a spectrum described by behavior. The data are in good agreement with the theoretically predicted pulsed shape, allowing the generation of a 1/f spectrum. Based on the data analysis and the theoretical description of the fluctuations, the origin of 1/f fluctuations in nonequilibrium conditions is explained by interactions resulting in correlations of carriers in two parallel channels as the common feature in the HEMT devices.

An improved stacking filtering for extracting the common-mode errors on GNSS coordinate time series in Shanxi

The presence of common mode error (CME) in the coordinate displacement time series of the Global Navigation Satellite System (GNSS) affects geophysical studies using GNSS observations. In order to investigate the effect of CME on the time series in GNSS networks in Shanxi, this paper proposes an improved superposition filtering method by introducing single-day solution accuracy, correlation coefficient, and spherical distance between stations as weights. The filtering effect is evaluated using the GNSS data in Shanxi. By using the improved stacking filtering method, the root mean square (RMS) values for N, E, U are reduced by approximately 27.8%, 29.0%, and 46.0%, respectively. And compared to the traditional stacking filter, our improved method can achieve better results with CME extraction. We investigate the CME spatial-temporal characteristics and its relationship with environmental loading. The results show that the CME between stations decreases as the distance between stations increases. In addition, we analyze the effect of CME on the noise component and velocity estimates. Results show that removing the CME refines the velocity and leads to a significant reduction in the magnitude of noise, indicating that the CME is dominated by the flicker noise in Shanxi Province.

Electrical Noise Analysis of Z Shape Horizontal Pocket and Hetero Stack TFETs under Trap Distribution

In this work, a comprehensive investigation on noise analysis for two different low power devices, namely Z-shaped Horizontal Pocket (ZHP) and Hetero Stack (HS) TFETs, is presented within low to high frequency range. The simulation is performed for these structures in the presence of Uniform and Gaussian trap distributions at the interface of Silicon and oxide materials for three different noise namely Flicker noise, Generation Recombination (GR) noise, and Diffusion noise with the help of the Sentaurus TCAD simulator. The result reveals that Flicker and GR noise are dominates at Low Frequency, while, the diffusion noise reports significant influence at the high-frequency range. Finally, a comparative analysis has been done in terms of noise current spectral density (Sid) of the considered structures with the existing literature.

Analysis of 1/f and G–R noise in Phosphorene FETs

This work deals with insights into low-frequency noise in phosphorene FETs. In addition to the flicker noise component, which is often reported in the literature, we also look at generation–recombination (G–R) noise. We evaluate the dependence of noise on the number of layers for both armchair (AC) and zigzag (ZZ) orientations. We also extract the noise parameters for this device.

Motion opponency at the middle temporal cortex: Preserved motion information and the effect of perceptual learning.

Motion opponency, first observed within the primate middle temporal cortex (MT), refers to the suppressing effect of opposite motion directions on neuronal activity. Namely, when opposing motion directional signals stimulate an MT neuron's receptive field, this neuron's response is comparable with that induced by flicker noise. Under such suppression, it is unknown whether any directional information is still represented at MT. In this study, we applied support vector machine (SVM) learning to human functional magnetic resonance imaging data to investigate if any motion defined orientation information was still available from suppressed MT. We found that, at least at the level of ±45° discrimination, such orientation information was still available. Interestingly, after behavioural perceptual learning that improved human discrimination of fine orientation discrimination (e.g. 42° vs. 48°) using the MT-suppressive motion stimuli, the SVM discrimination of ±45° worsened when functional magnetic resonance imaging (fMRI) signals at post-learning MT were used. This result is consistent with findings in Thompson et al. (2013) that, post-perceptual learning, MT suppression was not released, suggesting that motion opponency was perhaps functionally too important for perceptual learning to overcome.

Imperceptible Flicker Noise Reduction Using Pseudo-Flicker Weight Functionalized Derivative Equalization in Light-Fidelity Transmission Link.

A new technique to reduce flicker noise generated in light-fidelity (Li-Fi) transmission links based on the white light-emitting diode (LED) is proposed. Here, flicker noise with a frequency of 120 Hz, which is twice the frequency of AC power (60 Hz), is generated. The proposed technique is implemented in the receiver of the Li-Fi link. It can reduce flicker noise regardless of various digital modulation formats. In addition, there is no need to change the structure of the electrical circuit driving the LED to reduce the flicker noise. As a result, the non-return to-zero-on-off-keying (NRZ-OOK) signal waveform is tilted according to the flicker noise waveform. We implement the derivative equalization with a pseudo-flicker weight function to reduce the flicker noise. The derivative value of the NRZ-OOK signal mixed with flicker noise becomes larger than that without the flicker noise. In the proposed technique, the derivative value between adjacent sampling points is suppressed below the preset thresholds when it is greater than the preset threshold. Furthermore, a pseudo-flicker weight function is applied to accelerate the flicker noise reduction. As a result, using the proposed technique, a 2 dB signal-to-noise ratio (SNR) gain is obtained based on the bit error rate (BER) threshold (3.5 × 10-5) corresponding to 10% flicker modulation, which is known to have no serious effect on human health. This means that it is possible to implement a Li-Fi transmission link based on an illumination environment with a flicker modulation reduced from 10% to 7%.

Phase Noise Analysis of Separately Driven Ring Oscillators

In this paper, for the first time, the phase noise analysis of a Multi-loop Skew based Single Ended Oscillator (MSSROs) is derived and validated. Compared to the three stages of conventional ring oscillators (CROs), SDROs provide an equivalent oscillation frequency with improved phase noise with increasing stages. The primary distinction between these two designs (SDRO and three-stage CROs) is the inherent skew offset between the PMOS/NMOS gates caused by the unique connection. This skew offset is the fundamental cause of delay cell noise suppression; the SDROs have loosely coupled oscillators that run concurrently, forming multiple 3-stages of separately driven Ring Oscillators. As a result, a shaping function is derived in terms of skew offset, and simulating these with varying skew offset results in suppressing behavior. Additionally, we derived phase noise for a skew-based design and validated it in PDKs of 180nm and 65 nm. We plotted the thermal (flicker) noise contribution and found that increasing the number of stages leads to an approximately 1-2 dB reduction in phase noise while maintaining the same NMOS/PMOS size ratio. Finally, a 2-3 dB reduction in phase noise is achieved in MSSROs by incorporating the shaping function into phase noise equations.

An analytical model for electronic noise in a cryogenic bolometer detector readout circuit

This paper presents an analytical model to quantify the measured noise in a cryogenic bolometer readout circuit. The model includes the contributions from the bias resistors and sensor resistors, voltage and current noise of amplifier, and cable capacitance. The model parameters are empirically estimated using frequency domain analysis of the measured noise data of indigenously developed Neutron Transmutation Doped (NTD) Ge sensors. The model is shown to describe noise data for NTD Ge sensorsover a wide range of resistances corresponding to temperatures in the range 20–70 mK.Relative contributions of different components are discussed and it is shown that the contribution to the overall noise from the differential amplifier at 300 K is the dominant source. It is observed that the amplifier flicker noise is significantly lower than that specified in the amplifier datasheet. The present study also indicates that a desirable value of resistance of NTD sensor (R NTD) from noise considerations is ≲ 1 GΩ at ∼ 20 mK.

Pulse frequency fluctuations of persistent accretion powered pulsars

ABSTRACT In this study, we examine the long-term torque noise fluctuations of persistent X-ray binaries Her X-1, Vela X-1, GX 301-2, Cen X-3, 4U 1538-53, OAO 1657-415, and 4U 1626-67 using the historical pulse frequency measurements provided by CGRO/BATSE and Fermi/GBM. We find that known disc-fed sources exhibit a 1/ω2 red noise component in their power density spectra which is saturated over long time-scales. On the other hand, wind-fed sources form a clear white noise component, and the wind-fed sources with occasional transient disc formation imprint 1/ω type flicker noise. We discuss their long-term timing noise properties based on the models to describe the power density spectrum of pulse frequency derivative fluctuations in terms of monochromatic and coloured noise processes. Furthermore, we investigate the relation between measured timing noise strengths and other independently measured physical parameters. Despite the low number of sample sources, we suggest that the noise strengths of these sources are correlated with their luminosities and uncorrelated with their magnetic field strengths, implying that the dominant noise-generating mechanism is accretion.

Synergistic Approach of Interfacial Layer Engineering and READ-Voltage Optimization in HfO2-Based FeFETs for In-Memory-Computing Applications.

This article reports an improvement in the performance of the hafnium oxide-based (HfO2) ferroelectric field-effect transistors (FeFET) achieved by a synergistic approach of interfacial layer (IL) engineering and READ-voltage optimization. FeFET devices with silicon dioxide (SiO2) and silicon oxynitride (SiON) as IL were fabricated and characterized. Although the FeFETs with SiO2 interfaces demonstrated better low-frequency characteristics compared to the FeFETs with SiON interfaces, the latter demonstrated better WRITE endurance and retention. Finally, the neuromorphic simulation was conducted to evaluate the performance of FeFETs with SiO2 and SiON IL as synaptic devices. We observed that the WRITE endurance in both types of FeFETs was insufficient to carry out online neural network training. Therefore, we consider an inference-only operation with offline neural network training. The system-level simulation reveals that the impact of systematic degradation via retention degradation is much more significant for inference-only operation than low-frequency noise. The neural network with FeFETs based on SiON IL in the synaptic core shows 96% accuracy for the inference operation on the handwritten digit from the Modified National Institute of Standards and Technology (MNIST) data set in the presence of flicker noise and retention degradation, which is only a 2.5% deviation from the software baseline.

On Noise Modeling of Capacitive Feedback Transimpedance Amplifiers in CMOS

The work reports on the development of a detailed noise current model for a low-noise capacitive feedback transimpedance amplifier (TIA) in CMOS. The proposed TIA circuit implements the programmable-gain using an array of discretely controlled feedback capacitors and resistances in the biasing circuit and is originally designed bearing in mind low-noise requirements for optical time-domain reflectometer (OTDR) applications with the base gain of 10 kΩ at 1 GHz bandwidth and noise levels below 5.0 pA/Hz. The newly developed model for input-referred noise current spectral density complements the previously suggested transimpedance gain model and takes into account both the primary and secondary noise sources so far ignored in the models known in the literature. The proposed noise model consists of five terms and includes the effects caused by biasing components of the input stage and the noise shaping from the source follower. The performance of the developed noise model is evaluated using the post-layout simulation in 0.18 μm CMOS and 0.25 μm BiCMOS technologies, and a close match of the proposed model is demonstrated in the results of the post-layout simulation with the noise level below 1.8 pA/Hz for the base gain configuration in CMOS. A comparison to available noise models from the literature confirms that previously known noise models for this promising TIA architecture omitted important noise components present in practical and physically realizable circuits and, therefore, resulted in underestimating the base noise level by a factor of two to three, while completely ignoring the flicker noise mapping in the low-frequency range.

Improved Electrical Characteristics of AlGaN/GaN High-Electron-Mobility Transistor with Al2O3/ZrO2 Stacked Gate Dielectrics.

A metal-oxide-semiconductor high-electron-mobility transistor (MOS-HEMT) is proposed based on using a Al2O3/ZrO2 stacked layer on conventional AlGaN/GaN HEMT to suppress the gate leakage current, decrease flicker noise, increase high-frequency performance, improve power performance, and enhance the stability after thermal stress or time stress. The MOS-HEMT has a maximum drain current density of 847 mA/mm and peak transconductance of 181 mS/mm. The corresponding subthreshold swing and on/off ratio are 95 mV/dec and 3.3 × 107. The gate leakage current can be reduced by three orders of magnitude due to the Al2O3/ZrO2 stacked layer, which also contributes to the lower flicker noise. The temperature-dependent degradation of drain current density is 26%, which is smaller than the 47% of reference HEMT. The variation of subthreshold characteristics caused by thermal or time stress is smaller than that of the reference case, showing the proposed Al2O3/ZrO2 stacked gate dielectrics are reliable for device applications.

Performance Perspective of Gate-All-Around Double Nanosheet CMOS Beyond High-Speed Logic Applications

In this review paper, the performance characteristics of Gate-All-Around (GAA) double nanosheet (NS) MOSFETs are described over a broad temperature range, from 78 K to 473 K (200 oC). Emphasis is on the analog operation, showing good potential. Besides the transistor length, the impact of the metal gate Effective Work Function and the vertical distance between the nanosheets has been studied. Among others, a clear Zero Temperature Coefficient (ZTC) gate voltage has been observed that can be modeled by considering the shift with temperature of the threshold voltage and the maximum transconductance. A trade-off has been noticed between the transistor efficiency and the unit gain frequency, whereby the optimal operation point occurs in strong inversion regime. The feasibility of designing simple analog circuits has also been demonstrated. Finally, a detailed investigation of the low-frequency noise behavior yields good values for the flicker noise Power Spectral Density in comparison with other technology nodes.

A 516 μW, 121.2 dB-SNDR, and 125.1 dB-DR Discrete-Time Sigma-Delta Modulator with a 20 kHz BW

This article proposed a discrete-time single-loop 3rd order 5-bit Sigma-Delta (ΣΔ) modulator for the audio applications. In this modulator, a feed forward path is used to relax the design requirement of amplifier, which can reduce integrator’s output swing. And a 5-bit asynchronous SAR ADC combined with analog summing is adopted to quantify the summation of feedforward signal and loop filter output, which can significantly reduce power consumption. In addition, chopper stabilization technique is used to alleviate the flicker noise introduced by the first integrator. To eliminate the nonlinearity introduced by multibit quantizer, an improved data weighted average algorithm calibration circuit is proposed. The proposed modulator is implemented in 130 nm technology with a 1.12 mm2 core area. Operating at a 2.56MS/s sampling rate, post layout simulation results show that the modulator realizes 121.2-dB SNDR and 125.1-dB DR in a 20 kHz signal bandwidth, it dissipating 516 μW from 1.5 V supply. It also achieves the energy efficiency, as demonstrated by a Schreier figure of merit (FoMS) of 197 dB.

Ultrasensitive and high-speed AlGaN/AlN solar-blind ultraviolet photodetector: a full-channel-self-depleted phototransistor by a virtual photogate

High sensitivity, high solar rejection ratio, and fast response are essential characteristics for most practical applications of solar-blind ultraviolet (UV) detectors. These features, however, usually require a complex device structure, complicated process, and high operating voltage. Herein, a simply structured n-AlGaN/AlN phototransistor with a self-depleted full channel is reported. The self-depletion of the highly conductive n-AlGaN channel is achieved by exploiting the strong polarization-induced electric field therein to act as a virtual photogate. The resulting two-terminal detectors with interdigital Ohmic electrodes exhibit an ultrahigh gain of 1.3 × 10 5 , an ultrafast response speed with rise/decay times of 537.5 ps/3.1 μs, and an ultrahigh Johnson and shot noise (flicker noise) limited specific detectivity of 1.5 × 10 18 ( 4.7 × 10 16 ) Jones at 20-V bias. Also, a very low dark current of the order of ∼ pA and a photo-to-dark current ratio of above 10 8 are obtained, due to the complete depletion of the n - Al 0.5 Ga 0.5 N channel layer and the high optical gain. The proposed planar phototransistor combines fabrication simplicity and performance advantages, and thus is promising in a variety of UV detection applications.

σ-dominated charge transport in sub-nanometer molecular junctions

Quantum tunneling conductance of molecular junctions originates from the charge transport through the π-orbitals (π-transport) and the σ-orbitals (σ-transport) of the molecules, but the σ-transport can not be observed due to the more rapid decay of the tunneling conductance in the σ-system compared to that in the π-system. Here, we demonstrate that dominant σ-transport can be observed in π-conjugated molecular junctions at the sub-nanometer scale using the scanning tunneling microscope break junction technique (STM-BJ). We have found that the conductance of meta-connected picolinic acid, which mainly occurs by σ-transport, is ∼35 times higher than that of its para-isomer, which is entirely different from what is expected from π-transport through these systems. Flicker noise analysis reveals that the transport through the meta-connection exhibits more through-bond transport than the para-counterpart and density functional theory (DFT) shows that the σ-system provides the dominant transport path. These results reveal that the σ-electrons, rather than the π-electrons, can dominate charge transport through conjugated molecular junctions at the sub-nanometer scale, and this provides a new avenue toward the future miniaturization of molecular devices and materials.

A Low Phase Noise K-Band VCO With a Threshold Voltage-Based Current Source

This letter presents a low-phase-noise voltage-controlled oscillator (VCO) with a threshold-voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {TH}}$ </tex-math></inline-formula> )-based current source. The proposed current source is insensitive to the supply voltage, and the flicker noise of the transistor in the current source is decoupled, leading to lower phase noise to the resonator. In addition, a small-size differential inductor is adopted to diminish the resonator loss and to increase the quality factor. Fabricated in a 130-nm CMOS technology, the proposed VCO demonstrates a tuning range of 23.8–26.3 GHz (10.4%). It achieved a phase noise of −74.73 dBc/Hz at 100 kHz and −107.36 dBc/Hz at 1 MHz offset frequencies from the 24.005-GHz carrier frequency, respectively. The figure of merit (FoM) reaches −188 dBc/Hz.

σ-σ Stacked supramolecular junctions.

Intermolecular charge transport plays an essential role in organic electronic materials and biological systems. To date, experimental investigations of intermolecular charge transport in molecular materials and electronic devices have been restricted to conjugated systems in which π-π stacking interactions are involved. Herein we demonstrate that the σ-σ stacking interactions between neighbouring non-conjugated molecules offer an efficient pathway for charge transport through supramolecular junctions. The conductance of σ-σ stacked molecular junctions formed between two non-conjugated cyclohexanethiol or single-anchored adamantane molecules is comparable to that of π-π stacked molecular junctions formed between π-conjugated benzene rings. The current-voltage characteristics and flicker noise analysis demonstrate the existence of stacked molecular junctions formed between the electrode pairs and exhibit the characteristics of through-space charge transport. Density functional theory calculations combined with the non-equilibrium Green's function method reveal that efficient charge transport occurs between two molecules configured with σ-σ stacking interactions.

Overview of methods and means of implementation of information and measuring components cyber-physical systems for electromagnetic probing

The object of research is cyber-physical systems for the study of inhomogeneous environments, in particular, such as land and water depths, in order to find in them the leading bodies. One of the most problematic places in the creation of such systems is a highly sensitive meter of small phase shifts with a low sensitivity threshold. During the study, a review of methods for achieving a low threshold of sensitivity to phase shift. The main one is the method of converting the phase shift into the amplitude modulation coefficient. The implementation of the method is based on the sum-difference transformation with the preliminary introduction of the quadrature phase shift between the signals. The results concerning the methods of solving the following problems are obtained: – increasing the temperature stability of the quadrature phase shifter; – reducing the non-identity of the transmission coefficients of the sumo-difference scheme channels; – allocation of the amplitude of the amplitude-phase-modulated signal at low ratios of the frequencies of the input signals and switching. The first problem is partially solved by dividing the quadrature phase shifter into two equal halves, placed in different channels, with approximately the same phase temperature coefficients. The second problem is also solved by manual calibration before measurement. The most difficult task is to extract the bypass from the amplitude-phase-modulated signal, in which the carrier frequency is only several times greater than the bypass. The difficulty is that the detection produces combinational frequencies due to phase modulation. Therefore, it is difficult to separate them. Several methods of allocating the bypass, if the frequency of the input signals is fixed, are considered. This allows to get the sensitivity threshold(1·10–4÷3·10–5) of advice. Reducing the operating frequency of the signals increases the depth of research, but increases the impact of flicker noise. The minimum frequency is 10 Hz. Therefore, these methods are not suitable for frequencies of Hz units. Methods to reduce the impact of flicker noise will be considered in another paper.