Total Noise Power Research Articles

Sampling Circuits That Break the kT/C Thermal Noise Limit

Several circuit-level techniques are described which are used to reduce or cancel thermal noise and break the so-called kT/C limit. kT/C noise describes the total thermal noise power added to a signal when a sample is taken on a capacitor. In the first proposed technique, the sampled thermal noise is reduced by altering the relationship between the sampling bandwidth and the dominant noise source, providing a powerful, new degree of freedom in circuit design. In the second proposed technique, thermal noise sampled on an input capacitor is actively canceled using an amplifier, so that the noise at the amplifier output can be controlled independently of input capacitor size. Measurements from two test chips are presented which demonstrate sampled thermal noise power reduction of 48% and 67%, respectively, when compared with conventional kT/C-limited sampling.

Hot-electron noise features in silicon crystals operating under periodic signals

We study the intrinsic noise in n-type Si crystals operating under high-frequency periodic electric fields. To simulate the dynamics of electrons in the bulk, by taking into account the main details of band structure, scattering processes, as well as heating effects, a Monte Carlo approach is used. The noise properties are investigated by computing the velocity fluctuations correlation function, its spectral density, and the total noise power for different values of the amplitude and frequency of the driving field. We show that the noise features are significantly affected by the electric field amplitude and frequency and discuss their peculiarities in comparison with those exhibited in the static field case. We find the integrated spectral density, i. e. the total noise power, monotonically reducing its value with the increase of the field frequency, for each amplitude of the applied field. These results can be considered a first step towards a full understanding of the physical characteristics of electronic noise in Si devices, driven by periodic electric fields, relevant, for example, for harmonic generation purposes.

Hot-electron noise features in silicon crystals operating under periodic signals

We study the intrinsic noise in n-type Si crystals operating under high-frequency periodic electric fields. To simulate the dynamics of electrons in the bulk, by taking into account the main details of band structure, scattering processes, as well as heating effects, a Monte Carlo approach is used. The noise properties are investigated by computing the velocity fluctuations correlation function, its spectral density, and the total noise power for different values of the amplitude and frequency of the driving field. We show that the noise features are significantly affected by the electric field amplitude and frequency and discuss their peculiarities in comparison with those exhibited in the static field case. We find the integrated spectral density, i. e. the total noise power, monotonically reducing its value with the increase of the field frequency, for each amplitude of the applied field. These results can be considered a first step towards a full understanding of the physical characteristics of electronic noise in Si devices, driven by periodic electric fields, relevant, for example, for harmonic generation purposes.

Low Drop-Out Voltage Regulators: Capacitor-less Architecture Comparison

Demand for system-on-chip solutions has increased the interest in low drop-out (LDO) voltage regulators which do not require a bulky off-chip capacitor to achieve stability, also called capacitor-less LDO (CL-LDO) regulators. Several architectures have been proposed; however comparing these reported architectures proves difficult, as each has a distinct process technology and specifications. This paper compares CL-LDOs in a unified matter. We designed, fabricated, and tested five illustrative CL-LDO regulator topologies under common design conditions using 0.6?m CMOS technology. We compare the architectures in terms of (1) line/load regulation, (2) power supply rejection, (3) line/load transient, (4) total on-chip compensation capacitance, (5) noise, and (6) quiescent power consumption. Insights on what optimal topology to choose to meet particular LDO specifications are provided.

Active noise control system via multi-agent credit assignment

Multi-Agent systems have proved powerful in various sciences and engineering problems. This paper proposes a novel Multi-Agent Active Noise Control ANC formulation via the credit assignment approach. The introduced ANC removes multi-tonal acoustic noises in the environment invoking reinforcement learning techniques. In some multi-agent systems, for the training of all agents, only one reward is available. It is clear that this reward does not belong to one particular agent. The assignment of this reward to the agents is a problem which is known as Multi-Agent Credit Assignment MCA. In this research, each agent is responsible for reducing the noise power of one single harmonic, while only the total noise power of the signals is known. Therefore, it is required to assign a power contribution to each single harmonic. To resolve this problem, at first, the Knowledge Evaluation Based Critic Assignment KEBCA idea with proper modification is used and then a new method is introduced for this special problem. Simulation results show good improvement in the system performance by switching the single agent into the multi-agent system.

Optimal Timing at the Relay in OFDM Based Two Way Relay Systems

In amplify and forward (AF) two way relay networks (TWRN), two sources are allowed to transmit simultaneously in the multiple access time slot. Signal misalignment at the relay occurs due to the inaccurate time slot synchronization and different propagation delay. In broadband wireless communications, the misalignment could cover several symbol intervals. In orthogonal frequency division multiplexing (OFDM) based TWRN, such signal misalignment raises question on how to choose the fast Fourier transform (FFT) window at the relay node in order to minimize the interference which will be forwarded to the sources. In this paper, the timing issue of the received superimposed signal at the relay for both sources in OFDM based AF---TWRN is investigated. The optimal timing that minimizes the total interference power at the relay is studied. The imperfect timing induced interference power at each timing point is derived. An efficient estimator is proposed for the relay to decide where to establish the FFT window boundary in order to introduce the minimum interference plus noise power based on the superimposed training block from the two source nodes. The estimator is a sliding window estimator measuring the total interference plus noise power at each timing position, and the timing position which minimizes the metric function is the optimal position to establish the FFT window. Finally, the performance of the proposed estimator is evaluated by computer simulation in the presence of different amount of signal misalignment.

Research on the characteristics of noise source on heading face and noise propagation in mine laneway

Based on the complexity and dynamic random analysis of machine noise source in mine heading face, this article established the noise pressure mathematical model of noise propagation in mine laneway of different noise sources, carried out noise propagation numerical simulation in long space, and revealed noise propagation law of more radiated noise sources in the mine roadway. The results show that, under conditions that the total noise power is always the same, regardless of point source, surface noise source, or body noise source, the corresponding noise attenuation trend along the mine laneway and attenuation curve shape are basically the same. However, the attenuation velocity corresponding to complex stereo noise source is slower than single point source and the noise pressure value is higher than the single point source. The actual noise of measured values is close to the theoretical value or, say, there is little error for complex stereo noise source, whereas the error to single point source and surface noise is higher, respectively.

Anatomical complexity in breast parenchyma and its implications for optimal breast imaging strategies

The purpose of this investigation was to assess the anatomical noise in breast images using a mathematically derived parameter β as a surrogate for detection performance, across the same patient cohort but in different imaging modalities including mammography, tomosynthesis, and breast CT. Women who were scheduled for breast biopsy were approached for participation in this IRB and HIPPA-compliant investigation. A total of 23 women had all views of each modality and represent the cohort studied in this investigation. Image data sets across all modalities were analyzed using 1000 regions of interest per image data set, and the anatomical noise power spectrum, NPS(a)(f), was computed and averaged for each breast image data set. After windowing the total noise power spectrum NPS(t)(f) to a specific frequency range corresponding to anatomical noise, the power-law slope (β) of the NPS(a)(f) was computed where NPS(a)(f) = α f(-) (β). The value of β was determined for breast CT data sets, and they were 1.75 (0.424), 1.83 (0.352), and 1.79 (0.397), for the coronal, sagittal, and axial views, respectively. For tomosynthesis, β was 3.06 (0.361) and 3.10 (0.315) for the craniocaudal (CC) and medial lateral oblique (MLO) views, respectively. For mammography, these values were 3.17 (0.226) and 3.30 (0.236), for the CC and MLO views, respectively. The values of β for breast CT were significantly different than those for tomosynthesis and mammography (p < 0.001, all 12 comparisons). Based on the parameter β which is thought to describe anatomical noise in breast images, breast CT was shown to have a statistically significant lower β than mammography or tomosynthesis. It has been suggested in the literature that a lower β may correspond to increased cancer detection performance; however, this has yet to be demonstrated unequivocally.

PAPR reduction for LDPC coded OFDM systems using binary masks and optimal LLR estimation

A probabilistic PAPR reduction method using binary masks is proposed for OFDM systems. The binary masks are used to generate multiple signal candidates containing the same information. The candidate with the lowest PAPR is selected for transmission. In the presence of a non-linear amplifier (soft limiter), as the number of candidates increases, the PAPR is reduced, resulting in the reduction of clipping distortion power. Taking into account both distortion and channel noise, we derive the analytical total noise power to estimate the log-likelihood ratio (LLR), which is then used to enhance the decoding performance. We derive a minimum achievable E b / N 0 and a decoding threshold for LDPC codes in the presence of the soft limiter. Simulation results show that our LLR estimation improves the error performance, and multiple candidate system lowers the error rate.

Performance Analysis of M X N Equalizer Based Minimum Mean Square Error (MMSE) Receiver for MIMO Wireless Channel

The effect of fading and interference effects can be combated with equalizer. This paper analyses the performance of MMSE equalizer based receiver for MIMO wireless channel .The BER characteristics for the various transmitting and receiving antenna is simulated in mat lab tool box and many advantages and disadvantages the system is described. The simulation carried out signal processing lab show that the MMSE equalizer based receiver is a good choice for removing some ISI and minimizes the total noise power. The results show that the BER decreases as the m x n antenna configurations is increased. General Terms Equalizer, Bit error rate, Signal to noise ratio (eb/N0),transmitting antenna, receiving antenna

Convolutive Transfer Function Generalized Sidelobe Canceler

In this paper, we propose a convolutive transfer function generalized sidelobe canceler (CTF-GSC), which is an adaptive beamformer designed for multichannel speech enhancement in reverberant environments. Using a complete system representation in the short-time Fourier transform (STFT) domain, we formulate a constrained minimization problem of total output noise power subject to the constraint that the signal component of the output is the desired signal, up to some prespecified filter. Then, we employ the general sidelobe canceler (GSC) structure to transform the problem into an equivalent unconstrained form by decoupling the constraint and the minimization. The CTF-GSC is obtained by applying a convolutive transfer function (CTF) approximation on the GSC scheme, which is a more accurate and a less restrictive than a multiplicative transfer function (MTF) approximation. Experimental results demonstrate that the proposed beamformer outperforms the transfer function GSC (TF-GSC) in reverberant environments and achieves both improved noise reduction and reduced speech distortion.

A Model for Noise Power Nonlinearities in Perpendicular Magnetic Recording

Noise power versus linear density is modeled focusing solely on the magnetization fluctuations. The model examines the effect of mid-to high-density trunctation of the recorded magnetization transitions. At these densities, the medium becomes increasingly erased and the low density linear noise slope can vanish or even change sign. The slope of the total noise power versus density depends on a tradeoff of decreasing transition noise and increasing (AC) erasure noise. At high densities, the noise becomes dominated by the large medium erasure noise. The role of head-medium parameters is illustrated.

Noise analysis of coaxial Schottky barrier carbon nanotube fets using non equilibrium Green’s function formalism

Abstract The effect of noise on the performance of Schottky Barrier Carbon Nanotube Field Effect Transistors (SB-CNTFETs) has been investigated under various bias conditions. In order to calculate the noise power spectral density, the Non-Equilibrium Green’s Function formalism (NEGF) is used to obtain the transmission coefficient and the number of carriers inside the channel. Results are presented in two sections: In the first section the Hooge’s empirical rule is used to investigate the flicker noise properties of SB-CNTFETs with defects in the gate oxide region, while in the second section the thermal and shot noise properties of SB-CNTFETs are studied. Finally, the best bias points in the ON and OFF states have been suggested according to the total noise power spectral density and the device signal to noise ratio.

The influence of noise on electron dynamics in semiconductors driven by a periodic electricfield

Studies concerning the constructive aspects of noise and fluctuations in different non-linearsystems have shown that the addition of external noise to systems with an intrinsic noisemay result in a less noisy response. Recently, the possibility of reducing the diffusion noisein semiconductor bulk materials by adding a random fluctuating contribution to thedriving static electric field has been tested. The present work extends the previous theoriesby considering the noise-induced effects on the electron transport dynamics in low-dopedn-type GaAs samples driven by a high-frequency periodic electric field (cyclostationaryconditions). By means of Monte Carlo simulations, we calculate the changes in thespectral density of the electron velocity fluctuations caused by the addition ofan external correlated noise source. The results reported in this paper confirmthat, under specific conditions, the presence of a fluctuating component added toan oscillating electric field can reduce the total noise power. Furthermore, wefind a non-linear behaviour of the spectral density with the noise intensity. Ourstudy reveals that, critically depending on the external noise correlation time, thedynamical response of electrons driven by a periodic electric field benefits from theconstructive interplay between the fluctuating field and the intrinsic noise of thesystem.

Numerical study of the noise power of a carbon nanowire network

A thin film made of a carbon nanowire network can be mapped into a resistor network containing tunnel junctions that are randomly switched. In such a network the variance in individual resistance is infinity so the perturbative analysis must be applied on conductances. We study the relationship between the noise power and the network morphology through a Monte Carlo simulation of the conductance and the $1/f$ noise spectrum. We find that the noise power scales with the average current in a power law $S\ensuremath{\propto}{I}^{\ensuremath{-}\ensuremath{\omega}}$, where $\ensuremath{\omega}$ is a function of the network morphology. The noise spectrum is studied in detail, and we give a simple explanation for the observed relation between total noise power and the conductance.

Method for reducing noise in X-ray images by averaging pixels based on the normalized difference with the relevant pixel

A real-time digital filter for noise reduction in X-ray images is proposed. The filter is based on averaging of only similar pixels (pixels that differ only little) rather than neighboring pixels, which are averaged in conventional linear low-pass filters. The effectiveness of the filter was evaluated by computer simulation, where original images that were acquired by X-ray exposure were processed in accordance with the filter algorithm. The resulting images were evaluated in terms of the pre-sampled modulation transfer function (MTF), the noise power spectrum (NPS), and the lag. Comparison of the filtered and original images revealed that the NPS was reduced for the full range of spatial frequencies in the filtered image, resulting in a reduction of total noise power to about 1/9 the level in the original image with no degradation in the MTF or lag. The usefulness of the filter was demonstrated in fluoroscopic, digital subtraction angiography (DSA) and mammographic phantom studies. The filter was found to have the potential to reduce the patient dose by reducing the noise in dynamic as well as static X-ray images.

External Noise Effects on the Electron Velocity Fluctuations in Semiconductors

D. PERSANO ADORNO, N. PIZZOLATO AND B. SPAGNOLO Dipartimento di Fisica e Tecnologie Relative and CNISM, Group of Interdisciplinary Physics Viale delle Scienze, Ed. 18, Palermo, Italy We investigate the modification of the intrinsic carrier noise spectral density induced in low-doped semiconductor materials by an external correlated noise source added to the driving high-frequency periodic electric field. A Monte Carlo approach is adopted to numerically solve the transport equation by considering all the possible scattering phenomena of the hot electrons in the medium. We show that the noise spectra are strongly affected by the intensity and the correlation time of the external random electric field. Moreover this random field can cause a suppression of the total noise power.

On the Throughput Capacity of Large Wireless Ad Hoc Networks Confined to a Region of Fixed Area

We study the throughput capacity of large ad hoc networks confined to a square region of fixed area, thus exploring the dependence of the achievable throughput on the spatial node density. We find that there exists the value of the node density (the critical density) depending on the ratio of the total noise power to the transmit power such that the throughput increases as n(α-1)/2 at first, reaches a maximum, and then decreases as n-1/2.

PERFORMANCE ANALYSIS OF OS STRUCTURE OF CFAR DETECTORS IN FLUCTUATING TARGET ENVIRONMENTS

This paper is intended to the analysis of adaptive radar detectors for partially correlated χ 2 targets. This important class of targets is represented by the so-called moderately fluctuating Rayleigh targets, which, when illuminated by a coherent pulse train, return a train of correlated pulses with a correlation coefficient in the range 0 < ρ< 1 (intermediate between SWII and SWI models). The detection of this type of fluctuating targets is practically of great importance. Since the CFAR detectors represent an attractive class of schemes that can be used to overcome the problem of clutter by adaptively setting their threshold based on local information of total noise power, they are commonly used to decide the presence or absence of the radar target of interest, which is of partially correlated χ 2 type. In addition, the OS based algorithms are chosen to carry out this task owing to their immunity to outlying targets which may be present amongst the contents of the reference window. Moreover, since the large processing time of the single-window OS detector limits its practical applications, our scope here is to analyze the performance of OS modified versions for moderately fluctuating Rayleigh targets in nonideal situations. This analysis includes the single-window as well as the double-window OS detection schemes for the case where the radar receiver postdetection integrates M square-law detected pulses and the signal fluctuation obeys χ 2 statistics with two degrees of freedom. These detectors include the mean-level (ML-), the maximum (MX-) and the minimum (MN-) OS algorithms. Exact formulas for their detection probabilities are derived, in the absence as well as in the presence of spurious targets. The primary and the secondary interfering targets are assumed to be of the moderately fluctuating Rayleigh targets. Swerling's well known cases I and II represent the cases where the signal is completely correlated and completely decorrelated, respectively, from pulse to

Quantum theory of flicker noise in metal films

Flicker ( 1 / f γ ) voltage noise spectrum is derived from finite-temperature quantum electromagnetic fluctuations produced by elementary charge carriers in external electric field. It is suggested that deviations of the frequency exponent γ from unity, observed in thin metal films, can be attributed to quantum backreaction of the conducting medium on the fluctuating field of the charge carrier. This backreaction is described phenomenologically in terms of the effective momentum space dimensionality, D . Using the dimensional continuation technique, it is shown that the combined action of the photon heat bath and external field results in a 1 / f γ -contribution to the spectral density of the two-point correlation function of electromagnetic field. The frequency exponent is found to be equal to 1 + δ , where δ = 3 - D is a reduction of the momentum space dimensionality. This result is applied to the case of a biased conducting sample, and a general expression for the voltage power spectrum is obtained which possesses all characteristic properties of observed flicker noise spectra. The range of validity of this expression covers well the whole measured frequency band. Gauge independence of the power spectrum is proved. It is shown that the obtained results naturally resolve the problem of divergence of the total noise power. A detailed comparison with the experimental data on flicker noise measurements in metal films is given.