Flicker Noise Research Articles

Modeling GRACE-FO accelerometer data for the version 04 release

GRACE and GRACE-FO require the reduction of non-gravitational accelerations, through an onboard accelerometer, to accurately estimate variations in the Earth’s gravitational field. Accuracy in the accelerometer measurements is vital to this mass change recovery and significant errors will reduce the quality of the recovered science data. This paper describes our current characterization of error sources in the GRACE-FO accelerometers and the error mitigation strategies used in the generation of the JPL/CSR GRACE-FO Version 04 accelerometer data for public release. Our current error characterization model describes flicker noise on readings of one accelerometer plate pair on GRACE-D, impulse response limitations on both accelerometers, nonphysical once per revolution variations in the roll angular acceleration measurements on both accelerometers, significant correlated errors on all axes on GRACE-D, nominal thermal bias dependencies on both accelerometers, and expected nominal inter-measurement aliasing (cross-talk - expected as heritage from GRACE). Attitude reconstruction strategies incorporating star camera, inertial measurement unit, and magnetorquer measurements visibly improve angular acceleration recovery independent of the accelerometer. Error mitigation strategies for the linear acceleration measurements, associated with the calibrated accelerometer product provided in the version 04 release, dramatically improve estimates of the Earth’s gravity field. While many of the error characterizations described here are not necessary for constructing the accelerometer transplant from GRACE-C to GRACE-D, as is currently done in the Version 04 release, the error characterizations described here lay the groundwork for future use of calibrated/corrected GRACE-D accelerometer data.

Reaching the True Shot-Noise-Limited Phase Sensitivity in Self-Heterodyne Interferometry

The use of an acousto-optic modulator in an interferometer enables heterodyne detection and can alleviate technical issues such as laser intensity noise and photodetector flicker noise. However, it also introduces at least a 3 dB penalty to the shot-noise limited phase sensitivity when compared to that attainable through homodyne detection. In this paper, we show theoretically that this penalty can be lifted by implementing detection and demodulation schemes that exploit the cyclostationary nature of shot noise observed at the outputs of the self-heterodyne interferometer. We also discuss how expected departures from ideality, namely imperfect interferometric visibility, non-zero stationary noise, and finite detection bandwidth, affect the performance of these schemes and propose a simplified procedure relaxing the requirement for a rigorous instrument characterization. While two independent detectors are required to reach the true (classical-light) shot-noise limit for phase, single-detector instruments can also benefit from the introduced ideas to achieve up to 3 dB improvement in phase sensitivity.

Accurate Performance Evaluation of Jitter-Power FOM for Multiplying Delay-Locked Loop

An accurate performance evaluation of jitter-power figure-of-merit (FOM) for multiplying delay-locked loop (MDLL) is presented. For a typical MDLL employing a single-ended multiplying-delay ring voltage-controlled oscillator (MDVCO), it can be tuned via the capacitive loads to uphold a constant normalized phase noise (PN) across different frequencies for better jitter-power performance. Linear approximation and z-domain PN model are utilized to simplify the analysis with excellent agreement between the time-domain simulation and z-domain approximation. The influences of the asymmetric waveform, flicker noise corner, frequency error and reference noise are also discussed and then ignored based on the reasonable approximation. Under a given process, reference clock frequency and supply voltage, the ideal FOM can be derived theoretically. Based on these insights, the predicted FOM can be the benchmark metric in the design of MDLL for the possible best jitter-power performance.

Heterodyne terahertz detection based on antenna-coupled AlGaN/GaN high-electron-mobility transistor

In this article, we report an antenna-coupled AlGaN/GaN high-electron-mobility transistor integrated on a hyper-hemispheric silicon lens for heterodyne detection in a 340 GHz band at room temperature. The responsivity, elevated shot noise, flicker noise, and dynamic source-drain resistance for homodyne and heterodyne detection are characterized and analyzed at different local terahertz (LO) power levels. With a LO power of only −3.9 dBm, the detector offers a conversion loss less than 28 dB and a noise-equivalent power (NEP) about −132 dBm/Hz. A threshold LO power about −5 dBm is identified above which the shot noise becomes the dominant noise source, and the intermediate-frequency response is strongly suppressed. The elevated noise and the saturation in responsivity are found to be closely related to the strong direct-current homodyne current and the charge modulation/accumulation by the LO signal. Possible solutions are discussed to further reduce the NEP and the conversion loss.

Mg-doped beta-Ga2O3 films deposited by plasma-enhanced atomic layer deposition system for metal-semiconductor-metal ultraviolet C photodetectors

In this study, magnesium-doped gallium oxide (Ga2O3:Mg) films with various Mg contents were deposited by a plasma-enhanced atomic layer deposition (PE-ALD) system and were used as an active layer of metal-semiconductor-metal ultraviolet C photodetectors (MSM UVC-PDs). Compared with Ga element, owing to the lower electronegativity of Mg element, Mg–O bonds were more easily formed than Ga–O bonds. Consequently, oxygen vacancies could be reduced to improve properties. By using the measurement of X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL), the results verified that Ga2O3:Mg films with Mg content of 3.28 at.% had the lowest oxygen vacancy density. The cut-off wavelength of the devices was blue-shifted from 250 nm to 220 nm by increasing Mg content from 0 at.% to 5.22 at.%. The maximum photoresponsivity of 22.06, 10.24, 6.89, and 1.67 A/W was obtained for the devices with the Mg content of 0 at.%, 1.91 at.%, 3.28 at.%, and 5.22 at.%, respectively. The corresponding UV–visible rejection ratio was 3.56 × 104, 3.86 × 104, 4.42 × 104, and 3.48 × 103, respectively. The flicker noise was the dominant noise. By appropriately doping the Mg content in Ga2O3 films, the detectivity of the MSM UVC-PDs was effectively improved.

A random pulse modulation approach to modeling the flicker and white noise of the charge pump of a fractional‐N frequency synthesizer

SummaryFlicker noise and white noise from the charge pump (CP) within a phase locked loop (PLL) are key contributors to the close‐in phase noise floor of a fractional‐N frequency synthesizer. The pulse train from the phase frequency detector imposes different types of random pulse modulation on the up and down current sources, which causes different modulation effects to the flicker and white noises at low frequency. This paper rigorously analyzes the underlying noise random modulation mechanisms for the system operating in integer‐N and fractional‐N modes. Transient noise simulation using Verilog‐A behavioral modeling followed by power spectrum analysis is applied to support the mathematical analysis of the random noise modulation.

A Novel Current Density Based Design Approach of Low-Noise Amplifiers

The input-referred noise (IRN) is one of the most crucial performance indicators for the analog front-end (AFE) of neural recording devices. In this study, we present a novel design approach for a low-noise amplifier (LNA) based on the transistor optimization method in CMOS technology. Because flicker noise is predominant in neural recording applications, AFE has been designed to meet input-referred flicker noise specifications, whereas thermal noise contributions are monitored and controlled by flicker noise corner frequencies. Transistor optimization is accomplished using a lookup table that encapsulates its performance based on its current density. Initially, transistors are optimized based on the flicker noise performance; later, they may be further optimized based on their size, power consumption, transconductance, or thermal noise contribution. The proposed approach was validated by designing a folded-cascode amplifier with IRN ranging from 2 to 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{V}_{\text {rms}}$ </tex-math></inline-formula> . The results of the simulation show that the errors of our design methodology are less than 10%, which is less than those of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$g_{m}/I_{D} $ </tex-math></inline-formula> and inversion coefficient methods. The proposed LNA achieves 2.1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{V}_{\text {rms}}$ </tex-math></inline-formula> while consuming 0.83 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> from a 1.2 V supply.

NOISE FEATURES OF BREATH AND HEARTBEAT INFORMANT SIGNALS

Subject and Purpose. The subject of research is the flicker noise present in informant signals of search-and-rescue radars, specifically its properties and the effect it may have on algorithms for detecting and identifying manifestations of human breath and heartbeat processes during rescue operations. The work has been aimed at creating a suitable description of flicker noise for developing optimal algorithms of digital signal processing for quick detection and identification of informant signals during rescue missions. Method and Methodology. The low-frequency flicker noise has been modeled within the polynomial equations technique, proceeding from an analysis of real data on noise components in the output signals from a coherent search-and-rescue radar. A comparative analysis is done for a variety of approximating functions suggested for representing the low frequency portion of the spectrum observed. Results. For the low-frequency range wherein spectral components of the informative signal owing to respiration and heartbeat of humans are concentrated, an adequate model of the fluctuating interference is the flicker noise model built on the basis of polynomial equations. The problem of optimized model representation of the noise in digital signal processing algorithms has been analyzed for the case of a coherent search-and-rescue radar. A model of the fluctuating process has been suggested, based on a polynomial approximation for the spectral function in the low-frequency range of the signals observed at the radar output. Conclusion. Spectral characteristics of both interference and informant signals have been investigated. A structural diagram has been proposed for a high sensitivity, coherent search-and-rescue radar implementing a signal storage algorithm based on the polynomial model of the fluctuating process. The advantages and disadvantages of the radar are discussed, with examples given of real signal implementations and of noise spectrograms. Methods of effective estimation of Doppler signal phases are presented. The paper suggests an analysis of basic requirements as to parameters and performance characteristics of the rescue radar.

ОЦІНКА СПЕКТРАЛЬНОЇ ЩІЛЬНОСТІ ФЛІКЕР-ШУМУ МАЛОШУМІВНИХ ГЕНЕРАТОРІВ НА ІНФРАНИЗЬКИХ ЧАСТОТАХ

Subject and Purpose. Designers of the research radars intended for detecting manifestations of biological activity of living organisms may be interested in the noise characteristics shown by their oscillators at offsets about 10–2 Hz or even 10–3Hz from the carrier frequency. Unfortunately, the producing companies do not practice regular information on noise performance of their products at frequencies below 1 Hz. The present authors have set the goal of deriving an analytical expression for the spectral density of flicker noise which should allow radar engineers estimating the probable noise performance of low-noise oscillators over any frequency range. Methods and Methodology. A great number of writers considering spectral properties of flicker noise tend to support the assertion that its spectral density increases continuously with a decrease in frequency, following the power law 1/f . Meanwhile, the present authors assume availability of a certain frequencyfmbelow which the spectral density should most likely remain unchanged, even to as low as zero frequency. Also, there is a range of frequencies above which the spectral density of flicker noise remains constant and the total spectral density is determined solely by thermal noise. Results.The spectral density of noise follows the power law 1/f throughout the range fromfm and up to the point where thermal noise starts to overbalance the flicker noise. The authors have proposed an approximating function to describe the behavior of the averaged spectral density of noise from the oscillator within the entire frequency range. Conclusions. The results obtained shall allow radio system designers to make estimates of the probable noise performance of low-noise oscillators in any frequency range, using only known reference data provided by the manufacturer.

Analysis and Design of a Tetrahedral Oscillator

Analysis and design of a tetrahedral oscillator is presented. Expressions for the startup condition and oscillation frequency are derived. A phase noise analysis of thermal and flicker noise is carried out, using the impulse sensitivity function theory. The noise contribution of each type of transistor is studied, and the dominant and negligible cyclostationary noise sources are identified. There is good agreement among the theory and Spectre simulation. Design guidelines based on the analysis are provided.

Study of Optical and Gamma-ray Long-term Variability in Blazars

Blazars, a subset of powerful active galactic nuclei, feature relativistic jets that shine in a broadband electromagnetic radiation, e. g. from radio to TeV emission. Here I present the results of the studies that explore gamma-ray and optical variability properties of a sample of gamma-ray bright sources Several methods of time-series analyses are performed on the decade-long optical and Fermi/LAT observations. The main results are as follows: The sources are found highly variable in both the bands, and the gamma-ray power spectral density is found to be consistent with flicker noise suggesting long-memory processes at work. While comparing two emission, not only the overall optical and the $\gamma$-ray emission are highly correlated but also both the observation distributions exhibit heavy tailed log-normal distribution and linear RMS-flux relation. In addition, in some of the sources indications of quasi-periodic oscillation were revealed with similar characteristic timescales in both the bands. We discuss the results in light of current blazar models with relativistic shocks propagating down the jet viewed close to the line of sight.

The Evolution of the Charge Transport Mechanism in Single-Molecule Break Junctions Revealed by Flicker Noise Analysis.

The electronic noise characterization of single-molecule devices provides insights into the mechanisms of charge transport. In this work, it is reported that flicker noise can serve as an indicator of the time-dependent evolution of charge transport mechanisms in the single-molecule break junction process. By introducing time-frequency analysis, the authors find that flicker noise components of the molecule junction show time evolution behavior in the dynamic break junction process. A further investigation of the power-law dependence of flicker with conductance during the dynamic break junction process reveals that the mechanism of charge transport transits from the through-space transport to the through-bond transport, and is dominated by through-space transport again when the junction is about to rupture. The authors' results provide a flicker noise-based way to characterize the time-dependent evolution of charge transport mechanisms in single-molecule break junctions.

Ultra‐thin ISFET‐based sensing systems

AbstractThe ion‐sensitive field effect transistors (ISFETs), proposed little over 50 years ago, today make the most promising devices for lab‐on‐a‐chip, implantable, and point‐of‐care (POC) diagnostics. Their compatibility with CMOS (Complementary Metal Oxide Semiconductor) technology and the low cost through mass production have been the driving factors so far. Nowadays, they are also being developed in flexible form factors for new applications such as wearables and to improve the effective usage in existing applications such as implantable systems. In this regard, the CMOS ultra‐thin chip (UTC) technology and the bonding by printing are the noteworthy advances. This paper comprehensively reviews such new developments in the CMOS‐compatible ISFETs, along with their theory, readout circuitries, circuit‐based techniques for compensation of the ISFET's instabilities, such as the offset, flicker noise, and drift. The sensing mechanisms and the properties of interface between the electrolyte under test and the metal‐oxide based ion‐sensitive electrodes have been discussed along with a brief overview of the metal‐oxide based pH sensors. An overview of the reported mechanically flexible pH sensors, including ISFETs, is provided and the history of ISFET applications are also covered. Finally, established models that can be used to design flexible circuits are presented, and possible opportunities to use circuit techniques to compensate for mechanical deformation are discussed.

An ultra‐low power and low jitter frequency synthesizer for 5G wireless communication and IoE applications

AbstractThis paper presents a fully integrated analog phase‐locked loop (PLL) fractional‐N frequency synthesizer for 5G wireless communication and Internet‐of‐Everything (IoE) applications. To demonstrate the effectiveness of this frequency synthesizer, we apply it to three wireless communication standards. Contrary to using Verilog or VHDL to implement the programmable frequency divider, we propose a new approach in the transistor level with a new divide‐by‐2/3 circuit, dynamic asynchronous resettable D and JK flip‐flops, and the OR &amp; AND gates to customize the divider for low‐power, low‐jitter, and fast‐lock time applications. In addition, we have designed a new frequency phase detector (PFD) to overcome the dead region issue. An ultra‐low phase noise and low‐power voltage control oscillator (VCO) is exploited from our previous work with the flicker noise corner frequency around 10 kHz to achieve the lowest possible phase noise. The implementation is done in 180‐nm standard CMOS technology. It covers two frequency ranges including 2.4 to 2.48 GHz and 5 to 5.825 GHz for these wireless communication standards. According to simulations in the worst case, the lock time, rms‐jitter, in‐band fractional spur, power consumption, and jitter‐power figure‐of‐merit of the frequency synthesizer is 18 μs, 56 fs, −63 dBc, 4 mW, and −259, respectively.

Ultrahigh detectivity, high-speed and low-dark current AlGaN solar-blind heterojunction field-effect phototransistors realized using dual-float-photogating effect

High detectivity is essential for solar-blind deep-ultraviolet (DUV) light detection because the DUV signal is extremely weak in most applications. In this work, we report ultrahigh-detectivity AlGaN-based solar-blind heterojunction-field-effect phototransistors fabricated utilizing dual-float-photogating effect. The p + - Al 0.4 GaN layer and Al 0.4 GaN absorber layer deposited on the Al 0.6 GaN barrier serve as top pin-junction photogate, while the thin Al 0.4 GaN channel layer with a strong polarization field inside acts as virtual back photogate. Due to the effective depletion of the two-dimensional electron gas at the Al 0.6 Ga 0.4 N / Al 0.4 Ga 0.6 N heterointerface by the top photogate, the dark current was suppressed below 2 pA in the bias range of 0 to 10 V. A high photo-to-dark current ratio over 10 8 and an optical gain of 7.5 × 10 4 were demonstrated at a bias of 5 V. Theoretical analysis indicates that the optical gain can be attributed to the joint action of the floating top and back photogates on the channel current. As a result, a record high flicker noise (Johnson and shot noise) limited specific detectivity of 2.84 × 10 15 ( 2.91 × 10 17 ) cm Hz 0.5 W − 1 was obtained. Furthermore, high response speed at the microsecond level was also shown in the devices. This work provides a promising and feasible approach for high-sensitivity DUV detection.

Assessment of Fuel Cells’ State of Health by Low-Frequency Noise Measurements

We proposed applying low-frequency (flicker) noise in proton-exchange membrane fuel cells under selected loads to assess their state of health. The measurement set-up comprised a precise data acquisition board and was able to record the DC voltage and its random component at the output. The set-up estimated the voltage noise power spectral density at frequencies up to a few hundred mHz. We observed the evolution of the electrical parameters of selected cells of different qualities. We confirmed that flicker noise intensity varied the most (more than 10 times) and preceded changes in the impedance or a drop in the output DC voltage (less than 2 times). The data were observed for current loads (from 0.5 to 32 A) far from the permissible load. We deduce that the method can be utilised in industrial conditions to monitor the state of health of the selected cells by noise analysis. The method can be used in real-time when the flicker noise is measured within the range of a few Hz and requires a reasonable amount of averaging time to estimate its power spectral density. The presented method of flicker noise measurement has considerable potential for use in innovative ways of fuel cell quality monitoring.

A Low Phase Noise and High FoM Distributed-Swing-Boosting Multi-Core Oscillator Using Harmonic-Impedance-Expanding Technique

In this article, a distributed-swing-boosting and harmonic-impedance-expanding multi-core oscillator is proposed to achieve low phase noise and high figure-of-merit (FoM), simultaneously. First, a distributed-coupling multi-core topology is introduced to reduce the chip area with no mode ambiguity. Then, the distributed-swing-boosting and harmonic-impedance-expanding structure is developed to boost the gate swing and square-like waveform of <inline-formula> <tex-math notation="LaTeX">$V_{\text {DS}}$ </tex-math></inline-formula>. The common-mode (CM) resonances around the second harmonic and the differential-mode (DM) resonances around the third harmonic are utilized to suppress the flicker noise up-conversion and achieve harmonic shaping. Meanwhile, the dual-resonance response expands the high-impedance frequency ranges around the harmonics, and thus, the effect of harmonic shaping can be obtained over a wide frequency range. Fabricated in a 40-nm CMOS process, the oscillator measured exhibits low phase noise and high FoM simultaneously with a compact chip size. The minimum phase noise is &#x2212;138.9 dBc/Hz at the 1-MHz offset, corresponding to an FoM of 195.1 dBc/Hz. The 1/<inline-formula> <tex-math notation="LaTeX">$f^{3}$ </tex-math></inline-formula> phase noise corner is 100&#x2013;130 kHz over the 26.6&#x0025; tuning range.

Flicker noise in two-dimensional electron gas

Using the method developed in a recent paper (2019 Euro. Phys. J. B 92 1–28) we consider 1/f noise in two-dimensional electron gas (2DEG). The electron coherence length of the system is considered as a basic parameter for discretizing the space, inside which the dynamics of electrons is described by quantum mechanics, while for length scales much larger than it the dynamics is semi-classical. For our model, which is based on the Thomas-Fermi–Dirac approximation, there are two control parameters: temperature T and the disorder strength (Δ). Our Monte Carlo studies show that the system exhibits 1/f noise related to the electronic avalanche size, which can serve as a model for describing the experimentally observed flicker noise in 2DEG. The power spectrum of our model scales with the frequency with an exponent in the interval 0.3 < α PS < 0.6. We numerically show that the electronic avalanches are scale-invariant with power-law behaviors in and out of the metal-insulator transition line.

Gated Vernier delay line time integrator with applications in [formula omitted] time-to-digital converter

An all-digital bi-directional gated Vernier delay line (BDGVDL) time integrator with applications in all-digital ΔΣ time-to-digital converters (TDCs) is presented. The configuration and operation of the proposed Vernier time integrator are presented and its nonlinearity is analyzed. An in-depth treatment of the timing error of the time integrator due to supply, thermal, and flicker noise is provided. Design considerations including the impact of the latency and metastability of catch-detect DFFs are examined. The proposed time integrator is utilized in design of an all-digital single-bit ΔΣ TDC. Simulation results in both time and frequency domains confirm that the time integrator performs time integration and the gain of the integrator obtained in simulation agrees with that obtained from theoretical analysis. The TDC exhibits first-order noise-shaping with noise floor independent of the amplitude of the input. The dynamic range of the TDC is lower-bound by the difference between the per-stage-delay of the slow and fast lines and the nonlinearity of the delay stages of the time integrator and upper-bound by the number of the delay stages of the time integrator.

Ambipolar Gate Modulation Technique for the Reduction of Offset and Flicker Noise in Graphene Hall-Effect Sensors

There is a constant need for Hall-effect magnetic sensors with lower noise and lower offset for the high accuracy analog applications driven primarily by industrial and automotive markets, for example, high dynamic range current sensing for battery management in electric vehicles. Graphene-based Hall sensors (GHSs) demonstrate low thermal noise due to their high carrier mobility but suffer from large low-frequency flicker noise and offset limiting the prevalent low-frequency applications. In this paper, we present the results of a recently proposed gate modulation scheme for GHSs that uses dynamic ambipolar operation to up-convert the input magnetic signal to higher modulating frequencies while the offset and flicker noise remain spectrally unchanged and thus enabling thermal noise limited performance. We implement a prototype GHS using a scalable fabrication process with CVD graphene transferred on to silicon-oxide and followed by standard thin film and subsequent photolithographic processes. The measurement results confirm the effectiveness of dynamic ambipolar gate modulation technique in producing low offset of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 524\,\,\mu \mathrm{T}$ </tex-math></inline-formula> in conjunction with three orders of magnitude estimated improvement in the low frequency noise performance.