Noise Spectral Density Research Articles

An efficient design of 45-nm CMOS low-noise charge sensitive amplifier for wireless receivers

<p>Amplifiers are widely used in signal receiving circuits, such as antennas, medical imaging, wireless devices and many other applications. However, one of the most challenging problems when building an amplifier circuit is the noise, since it affects the quality of the intended received signal in most wireless applications. Therefore, a preamplifier is usually placed close to the main sensor to reduce the effects of interferences and to amplify the received signal without degrading the signal-to-noise ratio. Although different designs have been optimized and tested in the literature, all of them are using larger than 100 nm technologies which have led to a modest performance in terms of equivalent noise charge (ENC), gain, power consumption, and response time. In contrast, we consider in this paper a new amplifier design technology trend and move towards sub 100 nm to enhance its performance. In this work, we use a pre-well-known design of a preamplifier circuit and rebuild it using 45 nm CMOS technology, which is made for the first time in such circuits. Performance evaluation shows that our proposed scaling technology, compared with other scaling technology, extremely reduces ENC of the circuit by more than 95%. The noise spectral density and time resolution are also reduced by 25% and 95% respectively. In addition, power consumption is decreased due to the reduced channel length by 90%. As a result, all of those enhancements make our proposed circuit more suitable for medical and wireless devices.</p>

Phase Noise Spectral Density Measurement of Broadband Frequency-Modulated Radar Signals

In continuous-wave (CW) radar systems, such as frequency-modulated (FMCW), frequency-stepped (FSCW), or orthogonal frequency-division multiplexing (OFDM) radar systems, the range and velocity uncertainty are significantly impaired by phase noise decorrelation. Therefore, radar designers require accurate knowledge of their synthesizers’ phase noise profiles to assess and predict radar performance. However, commercial phase noise analyzers cannot determine phase noise during modulation, and this may differ notably from phase noise in the pure CW mode. Recent methods for FMCW phase noise analysis usually require comprehensive <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${a}$ </tex-math></inline-formula> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">priori</i> knowledge of modulation parameter and are prone to systematic deviations. To overcome these issues, we propose a new approach based on differential analysis of subsequent time-domain measurements. This method retains, statistical phase noise information while reducing systematic influences. For the first time, less <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${a}$ </tex-math></inline-formula> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">priori</i> signal knowledge is required, and the method works for nearly any kind of broadband signal modulation. The concept requires only a digitizer (e.g., an oscilloscope) and some digital signal processing. The proposed method is first experimentally tested with different phase-locked-loop (PLL)-based synthesizer phase noise profiles. The obtained phase noise profiles agree perfectly with the results of an established measurement system. After this proof of basic functionality, the unique phase noise analysis capability for BB modulated signals is demonstrated with PLL-generated FMCW signals. The results reveal a significant phase noise difference between the different setups and clearly show the capability and benefit of the novel phase noise spectral density measurement concept.

Role of gate electrode in influencing interface trap sensitivity in SOI tunnel FETs

This article reports the response of a silicon-on-insulator tunnel field-effect transistor (TFET) to the presence of semiconductor/ gate dielectric interface traps. A systematic strategy is designed keeping in view different parameters which are related to the gate of the device. Acceptor-like traps, and donor-like traps with Gaussian distribution are considered at the said interface for the entire analysis. Sensitivity % is taken as a figure of merit which measures the deviation of the drain current in presence of traps from the cases with no traps. The effect of temperature on interface traps, and the effect of interface traps on gate leakage current are analyzed. The acceptor-like traps are found to affect the on-state regime, and the donor-like traps are found to affect the ambipolar regime. Analyses on gate–drain underlap, gate–source overlap, shift of entire gate over the device, and gate work-function suggest that the gate electrode plays an important role in determining the sensitivity of the TFETs. Furthermore, noise spectral densities in presence of flicker, diffusion, and monopolar generation-recombination noise sources, and interface traps are reported.

SAW-Less Direct RF Transmitter With Multimode Noise Shaping and Tri-Level Time-Approximation Filter

This article presents a multimode direct radio frequency (RF) transmitter capable of a high in-band dynamic range and a low out-of-band (OOB) noise floor. It features a hybrid digital-to-analog converter (DAC) with a reconfigurable dual-band delta–sigma modulator to lower the quantization noise floor at one or two frequency bands. Additionally, a tri-level time-approximation filter is proposed to further suppress OOB noise with high tunability and stopband attenuation. The objective is to demonstrate a low-noise floor without using a surface acoustic wave (SAW) filter. For a 256-quadratic-amplitude modulation (QAM) signal with 17.4-dBm average output power at a 2.2-GHz carrier, the silicon prototype achieves −40-dB error vector magnitude (EVM) and −169-dBc/Hz noise spectral density (NSD) at 68-MHz offset by consuming a total power of 1.2 W.

Comparison of modified Woo’s solar phase scintillation model with ESA’s BepiColombo superior solar conjunction measurement data for X-band and Ka-band

Solar phase scintillation is of major interest in deep space mission operations for designing a communications system capable of transmitting signals when the path is close to the Sun, but also for improving the navigation under these conditions. The basis of this work is Woo’s solar phase scintillation theory which reported a useful model for the spectral power density of phase scintillations of a signal traveling through a medium close to the Sun. In this paper, Woo’s solar phase scintillation formula is used for the simulation of the spectral density of phase fluctuations induced by the Sun on coherent signals (uplink and downlink carriers are coherently related by a fractional ratio implemented by the spacecraft’s transponder), for the two downlink frequency bands supported by the ESA deep space mission BepiColombo. In particular, the model has been compared to measurement data collected at low Sun Earth Probe (SEP) angles during the superior solar conjunction campaign in March 2021 (in its cruise phase to Mercury). The comparison shows a good match between the phase noise spectral densities of the modified formula and measurement data, therefore, confirming that the formula can be used for the planning and verification of the future near Sun measurements.

Conditional noise deep learning for parameter estimation of gravitational wave events

We construct a Bayesian inference deep learning machine for parameter estimation of gravitational wave events of binaries of black hole coalescence. The structure of our deep Bayesian machine adopts the conditional variational autoencoder scheme by conditioning on both the gravitational wave strains and the variations of the amplitude spectral density (ASD) of the detector noise. We show that our deep Bayesian machine is capable of yielding posteriors compatible with the ones from the nested sampling method and better than the one without conditioning on the ASD. Our result implies that the process of parameter estimation can be accelerated significantly by deep learning even with large ASD drifting/variation. We also apply our deep Bayesian machine to the LIGO/Virgo O3 events, the result is compatible with the one by the traditional Bayesian inference method for the gravitational wave events with signal-to-noise ratios higher than typical threshold value. We also discuss some possible ways for future improvement.

Excess noise in high-current diamond diodes

We report the results of an investigation of low-frequency excess noise in high-current diamond diodes. It was found that the electronic excess noise of the diamond diodes is dominated by the 1/f and generation-recombination noise, which reveals itself as Lorentzian spectral features (f is the frequency). The generation-recombination bulges are characteristic of diamond diodes with lower turn-on voltages. The noise spectral density dependence on forward current, I, reveals three distinctive regions in all examined devices—it scales as I2 at the low (I &amp;lt; 10 μA) and high (I &amp;gt; 10 mA) currents and, rather unusually, remains nearly constant at the intermediate current range. The characteristic trap time constants, extracted from the noise data, show a uniquely strong dependence on current. Interestingly, the performance of the diamond diodes improves with the increasing temperature. The obtained results are important for the development of noise spectroscopy-based approaches for device reliability assessment for high-power diamond electronics.

Coherent fibre link for synchronization of delocalized atomic clocks.

Challenging experiments for tests in fundamental physics require highly coherent optical frequency references with suppressed phase noise from hundreds of kHz down to μHz of Fourier frequencies. It can be achieved by remote synchronization of many frequency references interconnected by stabilized optical fibre links. Here we describe the path to realize a delocalized optical frequency reference for spectroscopy of the isomeric state of the nucleus of Thorium-229 atom. This is a prerequisite for the realization of the next generation of an optical clock - the nuclear clock. We present the established 235 km long phase-coherent stabilized cross-border fibre link connecting two delocalized metrology laboratories in Brno and Vienna operating highly-coherent lasers disciplined by active Hydrogen masers through optical frequency combs. A significant part (up to tens of km) of the optical fibre is passing urban combined collectors with a non-negligible level of acoustic interference and temperature changes, which results in a power spectral density of phase noise over 105 rad2· Hz-1. Therefore, we deploy a digital signal processing technique to suppress the fibre phase noise over a wide dynamic range of phase fluctuations. To demonstrate the functionality of the link, we measured the phase noise power spectral density of a remote beat note between two independent lasers, locked to high-finesse stable resonators. Using optical frequency combs at both ends of the link, a long-term fractional frequency stability in the order of 10-15 between local active Hydrogen masers was measured as well. Thanks to this technique, we have achieved reliable operation of the phase-coherent fibre link with fractional stability of 7 × 10-18 in 103 s.

Consequences of quantum noise control for the relaxation resonance frequency and phase noise in heterogeneous Silicon/III\u2013V lasers

We have recently introduced a new semiconductor laser design which is based on an extreme, 99%, reduction of the laser mode absorption losses. In previous reports, we showed that this was achieved by a laser mode design which confines the great majority of the modal energy (> 99%) in a low-loss Silicon guiding layer rather than in highly-doped, thus lossy, III–V p{}^+ and n{}^+ layers, which is the case with traditional III–V lasers. The resulting reduced electron-field interaction was shown to lead to a commensurate reduction of the spontaneous emission rate by the excited conduction band electrons into the laser mode and thus to a reduction of the frequency noise spectral density of the laser field often characterized by the Schawlow–Townes linewidth. In this paper, we demonstrate theoretically and present experimental evidence of yet another major beneficial consequence of the new laser design: a near total elimination of the contribution of amplitude-phase coupling (the Henry alpha parameter) to the frequency noise at “high” frequencies. This is due to an order of magnitude lowering of the relaxation resonance frequency of the laser. Here, we show that the practical elimination of this coupling enables yet another order of magnitude reduction of the frequency noise at high frequencies, resulting in a quantum-limited frequency noise spectral density of 130 Hz^2/Hz (linewidth of 0.4 kHz) for frequencies beyond the relaxation resonance frequency 680 MHz. This development is of key importance in the development of semiconductor lasers with higher coherence, particularly in the context of integrated photonics with a small laser footprint without requiring any sort of external cavity.

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.

Wind speed and direction estimation based on the spatial coherence of closely spaced microphones.

Wind-induced noise recorded with a compact microphone array can be exploited to infer the mean velocity of the free-field airflow. In this work, a model-based method to estimate the wind flow speed and direction is proposed that uses spectro-spatial correlations of closely spaced microphone signals. As shown in a recent work by the present authors, the normalized cross-power spectral density of flow-induced noise measured with closely spaced microphones, also referred to as the spatial coherence, can be approximated by a semi-empirical model, named the Corcos model. Due to the dependency of the Corcos model on the airflow velocity, the measured spatial coherence provides information on the sought quantity. Speed and direction can be resolved by fitting the measured spatial coherence to the analytical Corcos model in the least squares sense. The accuracy of the proposed method is investigated across a range of wind speed between 0.5 and 12 ms-1 and all directions, using observation lengths from 5 s to 1 h. The audio samples under test were recorded indoors and outdoors and labeled by an ultrasonic anemometer. The evaluation results show that the accuracy can be increased by reducing the time resolution.

МОДЕРНИЗАЦИЯ СИНТЕЗАТОРОВ ЧАСТОТ РАДИОСТАНЦИИ УКВ РАДИОСВЯЗИ

Trends and prospects for the development of modern systems and complexes of radio communication, features of the use of frequency synthesizers based on the pulse-phase-locked loop in modern radio communications are analyzed. The results of the MF modernization on an integrated circuit HMC704 for transceivers of VHF radio stations are presented. The modeling of the upgraded midrange main units was carried out in the TI PLLatinumSim program. The LPF elements values and power spectral density of the output MF signal phase noise on LMX2594 IC are calculated. Due to the possibility of using a high comparison frequency in a frequency-phase detector, it was possible to improve the weight and size indicators, increase the speed and purity of the output signal spectrum of upgraded MF, which was confirmed by the results of modeling and experimental studies of the current synthesizer layout.

Влияние низкой температуры на электрофизические и шумовые характеристики ультрафиолетовых светодиодов на основе структур с квантовыми ямами InGaN/GaN

Comparison of optical power, external quantum efficiency in InGaN / GaN UV LEDs at room temperature and liquid nitrogen temperature is carried out. The spectral densities of the current low-frequency noise have been investigated. The mechanisms of carrier transport, the formation of low-frequency noise, and the dependences of the rates of radiative and nonradiative recombination at room and nitrogen temperatures are considered.

Influence of low temperature on the electrophysical and noise characteristics of UV LEDs based on InGaN/GaN quantum well structures

Comparison of optical power, external quantum efficiency in InGaN/GaN UV LEDs at room temperature and liquid nitrogen temperature is carried out. The spectral densities of the current low-frequency noise have been investigated. The mechanisms of carrier transport, the formation of low-frequency noise, and the dependences of the rates of radiative and nonradiative recombination at room and nitrogen temperatures are considered. Keywords: External quantum efficiency, low-frequency noise, carrier transport, defect tunneling.

Construction strategy of quantum air communication network of imitation goose swarm array

Quantum satellite communication is a research hotspot in the field of quantum communication, which has the characteristics of wide coverage, high communication efficiency and strong security. The construction strategy of the quantum communication network is an essential part of quantum communication. However, the construction strategy of quantum air communication network has not been studied yet so far. In this paper, according to the characteristics of flying goose array and principle of bionics, a simulated wild goose group Λ quantum air communication network topology is proposed, which can be divided into single-head node Λ type and multi-head node Λ type. Based on Greenberger-Horne-Zeilinger (GHZ) state particles, a certifiable QSDC inter-network communication system and a GHZ-EPR quantum teleportation communication system are established. The bit error rate, energy consumption, throughput, and other parameters are studied. After theoretical analysis and experimental measurement, for the single-head node Λ network structure in the environment where the average power spectral density of noise is 2 dB/m, when the communication distance between the head node and the child node is less than 400 m, the bit error rate is less than 0.094; if the communication distance increases from 400 m to 1000 m, the bit error rate increases rapidly, reaching 0.585; when the number of child nodes on one side increases from 2 to 7, the throughput decreases from 110.6 kb/s to 46.45 kb/s. For example, when the total number of nodes is 21, the single-head node Λ network structure saves 32.6% energy but reduces the throughput to 23.9 kb/s. By comparison, the multi-head node Λ network structure with 21 nodes saves 29.3% energy and achieves throughput of 163.4 kb/s. The above studies show that the quantum air network with the structure of imitation goose group array has good network scalability, excellent information security and flexible network structure.

Magnetic Sensing System for Potential Applications in Deep Earth Extremes for Long-Term Continuous Monitoring

Long-term monitoring of weak changes in the magnetic field in the deep part of the Earth, allows to detect anomalies related to the pre-natural disaster stage at the onset of the deformation of the earth’s crust. However, standard electronic instruments are unable to work under high temperatures and high-pressure harsh environments for a long time. To address this problem, an in-well magnetic field measurement system, including a three-axis “residence times difference” fluxgate magnetometer, a heat exchange system with a coolant, and a control module, is designed. The measured maximum sensor sensitivity at room temperature is 0.02 s/(A/m). The rms input noise is within ±2 nT, corresponding to a noise spectral density of 200 pT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> @1 Hz, that is sufficient to accurately detect the fluctuations of the geomagnetic field. The feasibility of the system was verified in laboratory at four temperatures, from 120°C to 210°C, corresponding to 2000 m - 5000m subsurface depths. When, in the experiments performed at 210 °C, the magnetic field was changed of some hundreds of nT, the sensor outputs responded very well in the three directions, with a dynamic detectability of few tens of nT. The control module maintains the internal temperature in the range 25 °C - 40 °C when the external temperature varies between 120 °C and 210°C, allowing a good long-term stability, as demonstrated by aging tests in laboratory. Finally, field experiments were conducted to verify the engineering feasibility of the system for ten days at 100 m depth and 15~18 °C.

Statistical Comparison of Ocean Wave Directional Spectra Derived From SWIM/CFOSAT Satellite Observations and From Buoy Observations

The comparison and verification of ocean wave spectrum by remote sensing and by in-situ measurements at the spectral level is quite rare, because the use of the traditional comparison method lead to very limited spatio-temporal matching pairs. In this paper, a new comparison method is proposed. With this method, under different sea conditions (wind wave mainly/swell mainly) and sea surface conditions (wind speed smaller than 20m/s, significant wave height from 1m to 7m), mean directional wave height spectra from SWIM (Surface Waves Investigation and Monitoring) are compared at the spectral level to the buoy counterparts, in different classes of sea-state. This includes the comparison of the omni-directional wave height spectrum and the directional function at the peak wave number. The comparison results show that under medium and high sea conditions, wave directional spectra provided by the SWIM beams at 8 &#x00B0; and 10 &#x00B0; incidence have a high consistency with those from buoy data. Under low sea conditions, the measurement bias of SWIM wave directional spectra mainly comes from three phenomena which are, by order of importance, an abnormal lifting of spectral energy caused by non- wave components at low wave numbers (parasitic peak), from the non-linear surfboard effect in the radar imaging mechanism and from a slight underestimation of speckle noise spectral density.

Influence of Analog-To-Digital Conversion and Decimation Parameters on the Signal-To-Noise Ratio in the Radar Path

Introduction. The digital representation of received radar signals has provided a wide range of opportunities for their processing. However, the used hardware and software impose some limits on the number of bits and sampling rate of the signal at all conversion and processing stages. These limitations lead to a decrease in the signal-to-interference ratio due to quantization noise introduced by powerful components comprising the received signal (interfering reflections; active noise interference), as well as the attenuation of a low-power reflected signal represented by a limited number of bits. In practice, the amplitude of interfering reflections can exceed that of the signal reflected from the target by a factor of thousands.Aim. In this connection, it is essential to take into account the effect of quantization noise on the signal-tointerference ratio.Materials and methods. The article presents expressions for calculating the power and power spectral density (PSD) of quantization noise, which take into account the value of the least significant bit of an analog-to-digital converter (ADC) and the signal sampling rate. These expressions are verified by simulating 4-, 8- and 16-bit ADCs in the Mathcad environment.Results. Expressions are derived for calculating the quantization noise PSD of interfering reflections, which allows the PSD to be taken into account in the signal-to-interference ratio at the output of the processing chain. In addition, a comparison of decimation options (by discarding and averaging samples) is performed drawing on the estimates of the noise PSD and the signal-to-noise ratio.Conclusion. Recommendations regarding the ADC bit depth and sampling rate for the radar receiver are presented.

Low-frequency noise characteristics of GaN vertical PIN diodes—Effects of design, current, and temperature

We report low-frequency noise characteristics of vertical GaN PIN diodes, focusing on the effects of the diode design, current, and temperature. The as-grown and regrown diodes, with and without surface treatment, have been studied. The noise in most of the GaN devices had a characteristic 1/f spectrum at high and moderate currents, while some devices revealed generation-recombination bulges at low currents (f is the frequency). The predominant trend of the noise spectral density, SI, dependence on the current was SI ∼ I. All tested GaN PIN diodes had rather low normalized noise spectral densities of 10−18–10−16 cm2/Hz (f = 10 Hz) at the current density J = 1 A/cm2 at room temperature. The noise temperature dependences at different currents revealed peaks at T = 375–400 K. Temperature, current, and frequency dependences of noise suggest that the noise mechanism is of the recombination origin. We argue that the noise measurements at low currents can be used to efficiently assess the quality of GaN PIN diodes.

Channel Distribution and Noise Characteristics of Distributed Acoustic Sensing Underwater Communications

Due to the power and transmission rate limitations, it is challenging to achieve underwater acoustic (UWA) communications over long distances from the unmanned underwater vehicle (UUV) to the shore station. As an alternative solution, the distributed acoustic sensing (DAS) underwater communication uses submarine optical cable to acquire and demodulate acoustic communication signals. There is little research on the channel and noise of DAS underwater communication. This paper analyzes the channel characteristics and the background noise of a DAS underwater communication system with armored optical cable based on the experimental measurements. Channel analysis shows that the envelope amplitudes of impulse responses follow the Burr distribution. The amplitudes get increased concentration at lower values as the sound source goes closer to the position right above the optical cable. Moreover, we observe that the received signals are influenced by the adjacent segments, leading to multiple arrivals within each acoustic bounce. Noise analysis shows that for frequencies lower than 1 kHz, unlike the Wenz noise spectrum primarily caused by shipping and wind, the −18 dB/octave decrease in power spectral density (PSD) of DAS noise is mainly caused by the equipment and cable themselves. The noise also exhibits full-band fluctuations. In underwater communications, full-band noise poses significant challenges for signal design. As far as we know, this article is the first report on the field experiment using a DAS underwater communication system equipped with armored optical cable, providing a reference for future underwater applications.