Noise Power Spectral Density Research Articles

(Invited) In-Depth Understanding of the Key Contributors to the Total Flicker Noise in Advanced Logic Devices

The aim of this work is to perform an in-depth analysis in order to identify the key contributors to the total flicker noise in advanced MOSFET technologies, e.g. UTBOX, Gate-all-around (GAA) nanowire or nanosheet FET devices. For all investigated devices of these technologies an increase of the flat-band noise power spectral density level with the increase of the applied gate voltage was observed. This may be related to the correlated carrier number and mobility fluctuations noise mechanisms and/or with additional access resistances noise contributions. Different existing models have been applied in order to identify the key 1/f noise mechanism. However, a discrepancy in the obtained 1/f noise contributors is highlighted, and leads to some questioning about which employed model is most accurate and gives good indications on the key contributors and estimated parameters of the total flicker noise.

Impact of Circuit Power on the Energy Efficiency of Massive Multiple-Input Multiple-Output (MIMO) Cellular Systems

Massive multiple-input multiple-output (MIMO) systems are designed to increase data capacity systems. However, there are growing social and economic concerns in developing these communication technologies. Energy efficient systems are desirable for these systems considering the costs and minimizing resources. Thus, the optimization of these approaches is significant in the advancement of green communication. This paper converges on the circuit power in modelling massive MIMO systems. Specifically, to apply various power consumption of the transceiver chains, to determine the desired power of the base station value for maximum energy efficiency, and to define the effects of a realistic circuit power consumption model in Massive MIMO systems. Mathematical models were developed, and the corresponding codes were simulated using MATLAB. Different processing schemes were also studied, namely, maximum ratio transmission/maximum ratio combining, and zero forcing for the perfect and imperfect single-cells scenario. In contrast, multiple cells consider different re-use factors. As observed, a low power wattage consumption of transceiver chains and base stations is desired to produce a more remarkable relative change in energy efficiency. Local oscillators' power usage is also recommended to be low wattage. Low-power systems utilize low energy consumption but not disregarding higher energy efficiency. Other factors in data throughput – bandwidth, transmit power, noise power spectral density, and path loss, can be studied to optimize energy-efficient massive MIMO systems.

VHF crystal oscillator noise Part 2. Experimental and calculated data

Problem statement. The noise of radar local oscillator reference oscillation sources often prevails among the noise of the local oscillator signals. At long ranges, this leads to significant distortion of the results of processing weak reflected signals in radars. One of the ways to reduce the noise of the local oscillator signals is the use of VHF crystal oscillators with a low noise level. Goal. To obtain equations for the power spectral density of phase noise, as well as for random deviations of the oscillation phase of a model of a VHF crystal oscillator. Results. Equations for the power spectral density of phase noise, as well as for random deviations of the oscillation phase of a model of a VHF crystal oscillator are obtained. Practical significance. These theoretical and practical results obtained allow a more selective approach to the selection of parameters of high-frequency crystal oscillators for use as sources of local oscillator oscillations.

High-speed digital-to-analogue converters phase noise modelling

The paper presents a mathematical model of the phase noise power spectral density of a high-speed digital-to-analogue converter. The shapes of the envelopes of the spectrum of the output signal in RFZ3, RFZ4 operating modes are given. The phase noise transfer coefficients for RFZ3, RFZ4 operating modes are obtained. The modelling of the power spectral density of phase noises in the studied operating modes was carried out. The analysis of the received dependences is carried out. It is concluded that RFZ3, RFZ4 modes of operation allow to obtain a lower level of PSD phase noise for images n = 1, 3, 4, 5, which indicates the possibility of generating high-frequency signals with a frequency that is 5-11 times higher than the generated frequency in NRZ mode without noise degradation.

Metasurface-Enabled Uncooled Silicon Germanium Oxide Infrared Microbolometers for Long-Wave Infrared Detection

This paper investigated metasurface enabled uncooled silicon germanium oxide (Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.425</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.512</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.063</sub> ) infrared (IR) microbolometers. The metasurface was used to engineer the IR absorption to achieve broadband or narrowband spectral response, eliminate the need for Fabry-Perot quarter wave resonant cavity typically used in conventional microbolometer under the pixel, and significantly improve the electrical performance of the temperature-sensing layer. This has facilitated the fabrication of the microbolometer with the supporting arms placed underneath the pixel without disrupting the Fabry-Perot cavity, and as a result, the supporting arms were fabricated with longer length without sacrificing the fill factor. The longer support arms reduced the thermal conductance between the microbolometer pixel and the underlying substrate and thus increased the voltage responsivity. The spectral responsivity and detectivity for the fabricated devices were measured in vacuum and demonstrated tunablility with narrow bands between 7 to 12 μm by changing the metasurface disk diameter and periodicity. The measured voltage responsivity, detectivity and thermal response time were > 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> V/W and > 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cm Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> /W and 2.01 ms to filtered blackbody infrared radiation between > 2 μm. The voltage noise power spectral density (PSD) of the fabricated devices were reduced by annealing the devices in vacuum.

3D backside integration of FinFETs: Is there an impact on LF noise?

This paper compares the low-frequency noise performance of backside integrated pFinFETs versus their regular frontside-only processed counterparts. We report that no degradation of the dominant flicker noise is observed, comparing front- versus backside processed transistors. At the same time, application of a post backside processing annealing step(s) is shown to enable an improvement of the DC input characteristics and the low-frequency noise power spectral density of the devices.

Photoresponse and noise characteristics of in-situ fabricated NiPc nanowire photodetectors

The interface between organic nanowires and metal layers plays a key role in determining the photoresponse and noise characteristics of organic nanowires. Herein, nickel phthalocyanine (NiPc) nanowires are self-aligned along parallel nanogrooves on a sapphire surface, and then photodetectors are fabricated in situ without post-growth transfer and alignment steps. This in-situ fabrication eliminates unpredictable factors associated with post-growth processing steps and allows us to focus on studying the influence of different nanowire-metal interfaces. Two different electrodes prepared by thermal evaporation deposition (TED) and etching-assisted transfer printing (ETP) are compared. While both electrodes ensure that NiPc nanowires exhibit a sensitive photoresponse in the 380–800 nm spectrum, the ETP electrodes result in higher sensitivity but an order of magnitude slower response due to the increased nanowire-metal interfacial capacitance. The noise power spectral density (PSD) confirms that for both photodetectors, the frequency-dependent 1/f noise dominates at frequencies below 10 kHz while the frequency-independent white noise increases significantly at higher frequencies. However, while the noise PSD of the photodetectors with TED electrodes remains stable with increasing temperature and bias, the noise PSD of the photodetectors with ETP electrodes increase by four to twelve orders of magnitude due to significantly increased electromigration and structural damage.

Hybrid synthesizer with two PLLs and DDS Part 2. Fine tuning circuit and main PLL

The use of a direct digital synthesizer (DDS) with a frequency converter in the frequency shift circuit of a hybrid synthesizer of high-frequency oscillations can significantly reduce its phase noise. This version of the frequency synthesizer (FS) has not been previously considered in known publications. There is a need to perform an analysis of existing circuits of hybrid FS with PLL to identify the elements that make the greatest contribution to the phase noise of the output oscillations, develop and experimentally test a FS with a low level of phase noise power spectral density. The performed calculations and experiments show that the use of a frequency shift circuit with frequency conversion based on a DDS operating in the first Nyquist zone in a hybrid frequency synthesizer makes it possible to minimize the effect of DDS phase noises on the FS phase noises. In this case, at frequencies of detuning from the carrier, where the flicker noise of the PFD of PLL circuits in cascade connection prevails, the contribution of the flicker noise of the PLL chips to the noise of the output oscillation of the FS will be equivalent. It is convenient to estimate the phase noise of the FS at the equivalent frequency, determined by the frequency of the phase detector and the division factor in the feedback circuit of the second (main) PLL ring. Taking into account the results of the first part of this work, the calculated relations obtained allow us to design hybrid frequency synthesizers with DDS and PLL with a low level of phase noise. The expressions obtained in the work for the phase noise of a hybrid FS and its components also make it possible to estimate the potentially achievable levels of FS phase noise and can be used in calculating the characteristics of oscillation sources and signal synthesizers.

BEYONDPLANCK

We present a Bayesian method for estimating instrumental noise parameters and propagating noise uncertainties within the global BEYONDPLANCKGibbs sampling framework, which we applied toPlanckLow Frequency Instrument (LFI) time-ordered data. Following previous works in the literature, we initially adopted a 1/fmodel for the noise power spectral density (PSD), but we found the need for an additional lognormal component in the noise model in the 30 and 44 GHz bands. We implemented an optimal Wiener-filter (or constrained realization) gap-filling procedure to account for masked data. We then used this procedure to both estimate the gapless correlated noise in the time-domain,ncorr, and to sample the noise PSD parameters,ξn = {σ0, fknee, α, Ap}. In contrast to previousPlanckanalyses, we assumed piecewise stationary noise only within each pointing period (PID), and not throughout the full mission, but we adopted the LFI Data Processing Center results as priors onαandfknee. We generally found best-fit correlated noise parameters that are mostly consistent with previous results, with a few notable exceptions. However, a detailed inspection of the time-dependent results has revealed many important findings. First and foremost, we find strong evidence for statistically significant temporal variations in all noise PSD parameters, many of which are directly correlated with satellite housekeeping data. Second, while the simple 1/fmodel appears to be an excellent fit for the LFI 70 GHz channel, there is evidence for additional correlated noise that is not described by a 1/fmodel in the 30 and 44 GHz channels, including within the primary science frequency range of 0.1–1 Hz. In general, most 30 and 44 GHz channels exhibit deviations from 1/fat the 2–3σlevel in each one-hour pointing period, motivating the addition of the lognormal noise component for these bands. For certain periods of time, we also find evidence of strong common mode noise fluctuations across the entire focal plane. Overall, we conclude that a simple 1/fprofile is not adequate for obtaining a full characterization of thePlanckLFI noise, even when fitted hour-by-hour, and a more general model is required. These findings have important implications for large-scale CMB polarization reconstruction with thePlanckLFI data and the current work is a first attempt at understanding and mitigating these issues.

Underwater Noise Modeling and Its Application in Noise Classification with Small-Sized Samples

Underwater noise classification is of great significance for identifying ships as well as other vehicles. Moreover, it is helpful in ensuring a marine habitat-friendly, noise-free ocean environment. But a challenge we are facing is the small-sized underwater noise samples. Because noise is influenced by multiple sources, it is often difficult to determine and label which source or which two sources are dominant. At present, research to solve the problem is focused on noise image processing or advanced computer technology without starting with the noise generation mechanism and modeling. Here, a typical underwater noise generation model (UNGM) is established to augment noise samples. It is established by generating noise with certain kurtosis according to the spectral and statistical characteristics of the actual noise and filter design. In addition, an underwater noise classification model is developed based on UNGM and convolutional neural networks (CNN). Then the UNGM-CNN-based model is used to classify nine types of typical underwater noise, with either the 1/3 octave noise spectrum level (NSL) or power spectral density (PSD) as the input features. The results show that it is effective in improving classification accuracy. Specifically, it increases the classification accuracy by 1.59%, from 98.27% to 99.86%, and by 2.44%, from 97.45% to 99.89%, when the NSL and PSD are used as the input features, respectively. Additionally, the UNGM-CNN-based method appreciably improves macro-precision and macro-recall by approximately 0.87% and 0.83%, respectively, compared to the CNN-based method. These results demonstrate the effectiveness of the UNGM established in noise classification with small-sized samples.

Estimation of instability induced by probe laser frequency noise in cold-atom microwave clocks

The influence of laser frequency noise on the stability of a compact cold-atom microwave clock was investigated theoretically in this study. The phase-noisy laser was characterized by a phase-diffusion field. Given the laser linewidth, the analytical expressions of the atomic covariance function and the noise power spectral density of the relative intensity noise transferred from the frequency noise were derived based on stochastic differential equations. Our results provide an effective method to estimate the impact of laser frequency noise on the stability of an integrating sphere cold atomic clock. This method can be extended to other cold atom detection cases.

Field-programmable-gate-array-based digital frequency stabilization of low-phase-noise diode lasers.

We present the comparison of a field-programmable-gate-array (FPGA) based digital servo module with an analog counterpart for the purpose of laser frequency stabilization to a high-finesse optical cavity. The transfer functions of both the digital and analog modules for proportional-integral-derivative control are measured. For the lasers stabilized to the cavity, we measure the singe-sideband power spectral density of fast phase noise by means of an optical beat with filtered light transmitted through the cavity. The comparison between the digital and analog modules is performed for two low-phase-noise diode lasers at 1120 and 665 nm wavelengths. The performance of the digital servo module compares well to the analog one for the lowest attained levels of 30 mrad for the integrated phase noise and 10-3 for the relative noise power. The laser linewidth is determined to be in the sub-kHz regime, only limited by the high-finesse cavity. Our work exploits the versatility of the FPGA-based servo module (STEMlab) when used with open-source software and hardware modifications. We demonstrated that such modules are suitable candidates for remote-controlled low-phase-noise applications in the fields of laser spectroscopy and atomic, molecular, and optical physics.

A Coupling Mechanism between Flicker Noise and Hot Carrier Degradations in FinFETs.

A coupling mechanism between flicker noise and hot carrier degradation (HCD) is revealed in this work. Predicting the flicker noise properties of fresh and aged devices is becoming essential for circuit designs, requiring an understanding of the fundamental noise behaviors. While certain models for fresh devices have been proposed, those for aged devices have not been reported yet because of the lack of a clear mechanism. The flicker noise of aged FinFETs is characterized based on the measure-stress-measure (MSM) method and analyzed from the device physics. It is found that both the mean and deviations of the noise power spectral density increase compared with the fresh counterparts. A coupling mechanism is proposed to explain the trap time constants, leading to the trap characterizations in their energy profiles. The amplitude and number of contributing traps are also changing and are dependent on the mode of HCD and determined by the position of the induced traps. A microscopic picture is developed from the perspective of trap coupling, reproducing well the measured noise of advanced nanoscale FinFETs. The finding is important for accurate flicker noise calculations and aging-aware circuit designs.

Effect of fast noise on the fidelity of trapped-ion quantum gates

High-fidelity single- and multiqubit operations compose the backbone of quantum information processing. This fidelity is based on the ability to couple single- or two-qubit levels in an extremely coherent and precise manner. A necessary condition for coherent quantum evolution is a highly stable local oscillator driving these transitions. Here we study the effect of fast noise, that is, noise at frequencies much higher than the local oscillator linewidth, on the fidelity of one- and two-qubit gates in a trapped-ion system. We analyze and measure the effect of fast noise on single-qubit operations, including resonant $\ensuremath{\pi}$ rotations and off-resonant sideband transitions. We further numerically analyze the effect of fast phase noise on the M\o{}lmer-S\o{}rensen two-qubit gate. We find a unified and simple way to estimate the performance of all of these operations through a single parameter given by the noise power spectral density at the qubit response frequency. While our analysis focuses on phase noise and on trapped-ion systems, it is relevant for other sources of fast noise as well as for other qubit systems in which spinlike qubits are coupled by a common bosonic field. Our analysis can help in guiding the design of quantum hardware platforms and gates, improving their fidelity towards fault-tolerant quantum computing.

Accurate evaluation of self-heterodyne laser linewidth measurements using Wiener filters.

Self-heterodyne beat note measurements are widely used for the experimental characterization of the frequency noise power spectral density (FN-PSD) and the spectral linewidth of lasers. The measured data, however, must be corrected for the transfer function of the experimental setup in a post-processing routine. The standard approach disregards the detector noise and thereby induces reconstruction artifacts in the reconstructed FN-PSD. We introduce an improved post-processing routine based on a parametric Wiener filter that is free from reconstruction artifacts, provided a good estimate of the signal-to-noise ratio is supplied. Building on this potentially exact reconstruction, we develop a new method for intrinsic laser linewidth estimation that is aimed at deliberate suppression of unphysical reconstruction artifacts. Our method yields excellent results even in the presence of strong detector noise, where the intrinsic linewidth plateau is not even visible using the standard method. The approach is demonstrated for simulated time series from a stochastic laser model including 1/f-type noise.

Adapting to noise distribution shifts in flow-based gravitational-wave inference

Deep learning techniques for gravitational-wave parameter estimation have emerged as a fast alternative to standard samplers---producing results of comparable accuracy. These approaches (e.g., DINGO) enable amortized inference by training a normalizing flow to represent the Bayesian posterior conditional on observed data. By conditioning also on the noise power spectral density (PSD) they can even account for changing detector characteristics. However, training such networks requires knowing in advance the distribution of PSDs expected to be observed and therefore can only take place once all data to be analyzed have been gathered. Here, we develop a probabilistic model to forecast future PSDs, greatly increasing the temporal scope of trained deep learning models. Using PSDs from the second LIGO-Virgo observing run (O2)---plus just a single PSD from the beginning of the third (O3)---we show that we can train a DINGO network to perform accurate inference throughout O3 (on 37 real events). We therefore expect this approach to be a key component to enable the use of deep learning techniques for low-latency analyses of gravitational waves.

Fluctuation-driven excess noise near superconducting phase transition

We discuss intrinsic mechanisms of nonequilibrium excess noise in superconducting devices and transition edge sensors. In particular, we present an overview of fluctuation-driven contributions to the current noise in the vicinity of the superconducting transition. We argue that sufficiently close to the critical temperature fluctuations of conductivity may become correlated provided that the rate of quasiparticle relaxation is slow as compared to dynamics of superconducting fluctuations. In this regime, fluctuations of conductivity adiabatically follow the fluctuations of the electron distribution. This leads to a substantial enhancement of current noise. The corresponding spectral power density of noise has a Lorentzian shape in the frequency domain while its magnitude scales proportionally to the inelastic relaxation time. It also sensitively depends on the dephasing and Ginzburg–Landau timescales. Further estimates suggest that this mechanism dominates over the conventional temperature fluctuations in the same range of parameters. To describe these effects microscopically, we use the nonequilibrium Keldysh technique in the semiclassical approximation of superconductivity with Boltzmann–Langevin random forces to account for correlations of fluctuations.

An Improved Noise Modeling Method Using a Quasi-Physical Zone Division Model for AlGaN/GaN HEMTs

Accurate characterization of transistor noise performance is significant for low-noise amplifier (LNA) design. The conventional empirical noise model contains too many fitting parameters and thus relies on a large number of on-wafer noise measurements, especially the ambient temperature effects modeling. In this article, an improved noise modeling method using the quasi-physical zone division (QPZD) theory is proposed. The boundary potential calculation in the traditional modeling method is improved by considering the effects of the charge depletion region when the transistor is in the ON-state, which can result in at least two orders of magnitude improvement in the accuracy of the noise power spectral density (PSD). With this improvement, the noise performance can be accurately predicted without adding any fitting parameters in the noise PSD models. Furthermore, ambient temperature modeling of the noise performance is realized by considering the ambient temperature effects of drain–source current <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {ds}}$ </tex-math></inline-formula> with a modified <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {off}}$ </tex-math></inline-formula> model and some other significant intrinsic parameters. Verification shows that the proposed QPZD noise model with the improved boundary potential calculation method can well predict the noise performance and scattering parameters at different ambient temperatures. The method of this study can be applied to physical-based noise modeling of GaN high-electron-mobility transistors (HEMTs) and LNA design.

Intensity noise in difference frequency generation-based tunable femtosecond MIR sources.

We characterize the intensity noise of two mid-infrared (MIR) ultrafast tunable (3.5-11 μm) sources based on difference frequency generation (DFG). While both sources are pumped by a high repetition rate Yb-doped amplifier delivering 200 μJ 300 fs at a central wavelength of 1030 nm, the first is based on intrapulse DFG (intraDFG), and the second on DFG at the output of an optical parametric amplifier (OPA). The noise properties are assessed through measurement of the relative intensity noise (RIN) power spectral density and pulse-to-pulse stability. The noise transfer mechanisms from the pump to the MIR beam is empirically demonstrated. As an example, improving the pump laser noise performance allows reduction of the integrated RIN (IRIN) of one of the MIR source from 2.7% RMS down to 0.4% RMS. The intensity noise is also measured at various stages and in several wavelength ranges in both laser system architectures, allowing us to identify the physical origin of their variation. This study presents numerical values for the pulse to pulse stability, and analyze the frequency content of the RINs of particular importance for the design of low-noise high repetition rate tunable MIR sources and future high performance time-resolved molecular spectroscopy experiments.

A novel modem model insensitive to the effect of the modulated carrier and the demodulated-signal phase adapted for capacitive sensors

The differential bridge-type capacitive sensors are widely applied in many precise instrumental measurement fields, where the modem is a key technology to realize the detection for a tiny differential capacitance. A universal structure based on a modulated sine carrier and a switched analog demodulation is adopted, so two factors including the carrier’s stability and the slight phase difference with its fluctuation between demodulated signals will inevitably limit the modem performance, and further deteriorate the capacitance sensitivity. In this paper, a novel modem based on a modulated step sine carrier is proposed, and the theoretical analysis indicates that the novel structure can significantly reduce the effects of aforesaid factors. Finally, a joint evaluation circuit is built to preliminarily measure the modem noise, and experimental results demonstrate a relative voltage noise power spectral density of 7 ppm/Hz1/2 at 1 mHz for the novel modem, two times better than that with a sine carrier.