Showing papers on "Noise (electronics) published in 2000"

Modal Identification of Output-Only Systems using Frequency Domain Decomposition

Abstract: In this paper a new frequency domain technique is introduced for the modal identification of output-only systems, i.e. in the case where the modal parameters must be estimated without knowing the input exciting the system. By its user friendliness the technique is closely related to the classical approach where the modal parameters are estimated by simple peak picking. However, by introducing a decomposition of the spectral density function matrix, the response spectra can be separated into a set of single degree of freedom systems, each corresponding to an individual mode. By using this decomposition technique close modes can be identified with high accuracy even in the case of strong noise contamination of the signals. Also, the technique clearly indicates harmonic components in the response signals.

Image quality assessment based on a degradation model

Abstract: We model a degraded image as an original image that has been subject to linear frequency distortion and additive noise injection. Since the psychovisual effects of frequency distortion and noise injection are independent, we decouple these two sources of degradation and measure their effect on the human visual system. We develop a distortion measure (DM) of the effect of frequency distortion, and a noise quality measure (NQM) of the effect of additive noise. The NQM, which is based on Peli's (1990) contrast pyramid, takes into account the following: 1) variation in contrast sensitivity with distance, image dimensions, and spatial frequency; 2) variation in the local luminance mean; 3) contrast interaction between spatial frequencies; 4) contrast masking effects. For additive noise, we demonstrate that the nonlinear NQM is a better measure of visual quality than peak signal-to noise ratio (PSNR) and linear quality measures. We compute the DM in three steps. First, we find the frequency distortion in the degraded image. Second, we compute the deviation of this frequency distortion from an allpass response of unity gain (no distortion). Finally, we weight the deviation by a model of the frequency response of the human visual system and integrate over the visible frequencies. We demonstrate how to decouple distortion and additive noise degradation in a practical image restoration system.

Nonlinear limits to the information capacity of optical fiber communications

Abstract: The exponential growth in the rate at which information can be communicated through an optical fiber is a key element in the so called information revolution. However, like all exponential growth laws, there are physical limits to be considered. The nonlinear nature of the propagation of light in optical fiber has made these limits difficult to elucidate. Here we obtain basic insights into the limits to the information capacity of an optical fiber arising from these nonlinearities. The key simplification lies in relating the nonlinear channel to a linear channel with multiplicative noise, for which we are able to obtain analytical results. In fundamental distinction to the linear additive noise case, the capacity does not grow indefinitely with increasing signal power, but has a maximal value. The ideas presented here have broader implications for other nonlinear information channels, such as those involved in sensory transduction in neurobiology. These have been often examined using additive noise linear channel models, and as we show here, nonlinearities can change the picture qualitatively.

Hybrid integrated circuit device

Abstract: Disclosed is a hybrid integrated circuit device provided with an active filter. The active filter is constructed mainly from a rectifier circuit, a reactor with one terminal connected with an output terminal of the rectifier, a switching element connected with one terminal of the reactor and a smoothing condenser connected with the other terminal of the reactor. The active filter is mounted on an insulating metal substrate and has, other than the above feature, a specific circuit structure wherein the substrate is divided by a ground pattern or power supply pattern into two blocks. One block is for a large current circuit such as the rectifier circuit, the switching element, and a diode and another block for a small signal circuit such as a control circuit. The hybrid integrated circuit device is of remarkably compact size. Also, it is greatly superior in a noise performance because switching noise does not flow into the chassis of electronic equipment from the metal substrate and the control circuit is shielded from the noise produced by the large current circuit, and also because the noise caused by wiring inductance can be limited.

Optical Quantum Random Number Generator

Abstract: A physical random number generator based on the intrinsic randomness of quantum mechanics is described. The random events are realized by the choice of single photons between the two outputs of a beam splitter. We present a simple device, which minimizes the impact of the photon counters' noise, dead-time and after pulses.

MOS transistor modeling for RF IC design

Abstract: This paper presents the basis of the modeling of the MOS transistor for circuit simulation at RF. A physical equivalent circuit that can easily be implemented as a Spice subcircuit is first derived. The subcircuit includes a substrate network that accounts for the signal coupling occurring at HF from the drain to the source and the bulk. It is shown that the latter mainly affects the output admittance Y22. The bias and geometry dependence of the subcircuit components, leading to a scalable model, are then discussed with emphasis on the substrate resistances. Analytical expressions of the Y parameters are established and compared to measurements made on a 0.25-/spl mu/m CMOS process. The Y parameters and transit frequency simulated with this scalable model versus frequency, geometry, and bias are in good agreement with measured data. The nonquasi-static effects and their practical implementation in the Spice subcircuit are then briefly discussed. Finally, a new thermal noise model is introduced. The parameters used to characterize the noise at HF are then presented and the scalable model is favorably compared to measurements made on the same devices used for the S-parameter measurement.

A 5-GHz CMOS wireless LAN receiver front end

Abstract: This paper presents a 12.4-mW front end for a 5-GHz wireless LAN receiver fabricated in a 0.24-/spl mu/m CMOS technology. It consists of a low-noise amplifier (LNA), mixers, and an automatically tuned third-order filter controlled by a low-power phase-locked loop. The filter attenuates the image signal by an additional 12 dB beyond what can be achieved by an image-reject architecture. The filter also reduces the noise contribution of the cascode devices in the LNA core. The LNA/filter combination has a noise figure of 4.8 dB, and the overall noise figure of the signal path is 5.2 dB. The overall IIP3 is -2 dBm.

Optimal transmit-receiver design in the presence of signal-dependent interference and channel noise

Abstract: Optimal detection of a target return contaminated by signal-dependent interference, as well as additive channel noise, requires the design of a transmit pulse f(t) and a receiver impulse response h(t) jointly maximizing the output signal to interference plus noise ratio (SINR). Despite the highly nonlinear nature of this problem, it has been possible to show that f(t) may always be chosen minimum-phase. A full analysis concludes with the construction of an effective numerical procedure for the determination of optimal pairs (f,h) that appears to converge satisfactorily for most values of input SINR. Extensive simulation reveals that the shape of f(t) can be a critical factor. In particular, the performance of a chirp-like pulse is often unacceptable, especially when clutter and channel noise are low-pass dominant and comparable.

Electromagnetic Noise and Quantum Optical Measurements

Abstract: 1. Maxwell's Equations, Power, and Energy.- 1.1 Maxwell's Field Equations.- 1.2 Poynting's Theorem.- 1.3 Energy and Power Relations and Symmetry of the Tensor.- 1.4 Uniqueness Theorem.- 1.5 The Complex Maxwell's Equations.- 1.6 Operations with Complex Vectors.- 1.7 The Complex Poynting Theorem.- 1.8 The Reciprocity Theorem.- 1.9 Summary.- Problems.- Solutions.- 2. Waveguides and Resonators.- 2.1 The Fundamental Equations of Homogeneous Isotropic Waveguides.- 2.2 Transverse Electromagnetic Waves.- 2.3 Transverse Magnetic Waves.- 2.4 Transverse Electric Waves.- 2.4.1 Mode Expansions.- 2.5 Energy, Power, and Energy Velocity.- 2.5.1 The Energy Theorem.- 2.5.2 Energy Velocity and Group Velocity.- 2.5.3 Energy Relations for Waveguide Modes.- 2.5.4 A Perturbation Example.- 2.6 The Modes of a Closed Cavity.- 2.7 Real Character of Eigenvalues and Orthogonality of Modes.- 2.8 Electromagnetic Field Inside a Closed Cavity with Sources.- 2.9 Analysis of Open Cavity.- 2.10 Open Cavity with Single Input.- 2.10.1 The Resonator and the Energy Theorem.- 2.10.2 Perturbation Theory and the Generic Form of the Impedance Expression.- 2.11 Reciprocal Multiports.- 2.12 Simple Model of Resonator.- 2.13 Coupling Between Two Resonators.- 2.14 Summary.- Problems.- Solutions.- 3. Diffraction, Dielectric Waveguides, Optical Fibers, and the Kerr Effect.- 3.1 Free-Space Propagation and Diffraction.- 3.2 Modes in a Cylindrical Piecewise Uniform Dielectric.- 3.3 Approximate Approach.- 3.4 Perturbation Theory.- 3.5 Propagation Along a Dispersive Fiber.- 3.6 Solution of the Dispersion Equation for a Gaussian Pulse.- 3.7 Propagation of a Polarized Wave in an Isotropic Kerr Medium.- 3.7.1 Circular Polarization.- 3.8 Summary.- Problems.- Solutions.- 4. Shot Noise and Thermal Noise.- 4.1 The Spectrum of Shot Noise.- 4.2 The Probability Distribution of Shot Noise Events.- 4.3 Thermal Noise in Waveguides and Transmission Lines.- 4.4 The Noise of a Lossless Resonator.- 4.5 The Noise of a Lossy Resonator.- 4.6 Langevin Sources in a Waveguide with Loss.- 4.7 Lossy Linear Multiports at Thermal Equilibrium.- 4.8 The Probability Distribution of Photons at Thermal Equilibrium.- 4.9 Gaussian Amplitude Distribution of Thermal Excitations.- 4.10 Summary.- Problems.- Solutions.- 5. Linear Noisy Multiports.- 5.1 Available and Exchangeable Power from a Source.- 5.2 The Stationary Values of the Power Delivered by a Noisy Multiport and the Characteristic Noise Matrix.- 5.3 The Characteristic Noise Matrix in the Admittance Representation Applied to a Field Effect Transistor.- 5.4 Transformations of the Characteristic Noise Matrix.- 5.5 Simplified Generic Forms of the Characteristic Noise Matrix.- 5.6 Noise Measure of an Amplifier.- 5.6.1 Exchangeable Power.- 5.6.2 Noise Figure.- 5.6.3 Exchangeable Power Gain.- 5.6.4 The Noise Measure and Its Optimum Value.- 5.7 The Noise Measure in Terms of Incident and Reflected Waves.- 5.7.1 The Exchangeable Power Gain.- 5.7.2 Excess Noise Figure.- 5.8 Realization of Optimum Noise Performance.- 5.9 Cascading of Amplifiers.- 5.10 Summary.- Problems.- Solutions.- 6. Quantum Theory of Waveguides and Resonators.- 6.1 Quantum Theory of the Harmonic Oscillator.- 6.2 Annihilation and Creation Operators.- 6.3 Coherent States of the Electric Field.- 6.4 Commutator Brackets, Heisenberg's Uncertainty Principle and Noise.- 6.5 Quantum Theory of an Open Resonator.- 6.6 Quantization of Excitations on a Single-Mode Waveguide.- 6.7 Quantum Theory of Waveguides with Loss.- 6.8 The Quantum Noise of an Amplifier with a Perfectly Inverted Medium.- 6.9 The Quantum Noise of an Imperfectly Inverted Amplifier Medium.- 6.10 Noise in a Fiber with Loss Compensated by Gain.- 6.11 The Lossy Resonator and the Laser Below Threshold.- 6.12 Summary.- Problems.- Solutions.- 7. Classical and Quantum Analysis of Phase-Insensitive Systems.- 7.1 Renormalization of the Creation and Annihilation Operators.- 7.2 Linear Lossless Multiports in the Classical and Quantum Domains.- 7.3 Comparison of the Schrodinger and Heisenberg Formulations of Lossless Linear Multiports.- 7.4 The Schrodinger Formulation and Entangled States.- 7.5 Transformation of Coherent States.- 7.6 Characteristic Functions and Probability Distributions.- 7.6.1 Coherent State.- 7.6.2 Bose-Einstein Distribution.- 7.7 Two-Dimensional Characteristic Functions and the Wigner Distribution.- 7.8 The Schrodinger Cat State and Its Wigner Distribution.- 7.9 Passive and Active Multiports.- 7.10 Optimum Noise Measure of a Quantum Network.- 7.11 Summary.- Problems.- Solutions.- 8. Detection.- 8.1 Classical Description of Shot Noise and Heterodyne Detection.- 8.2 Balanced Detection.- 8.3 Quantum Description of Direct Detection.- 8.4 Quantum Theory of Balanced Heterodyne Detection.- 8.5 Linearized Analysis of Heterodyne Detection.- 8.6 Heterodyne Detection of a Multimodal Signal.- 8.7 Heterodyne Detection with Finite Response Time of Detector.- 8.8 The Noise Penalty of a Simultaneous Measurement of Two Noncommuting Observables.- 8.9 Summary.- Problems.- Solutions.- 9. Photon Probability Distributions and Bit-Error Rate of a Channel with Optical Preamplification.- 9.1 Moment Generating Functions.- 9.1.1 Poisson Distribution.- 9.1.2 Bose-Einstein Distribution.- 9.1.3 Composite Processes.- 9.2 Statistics of Attenuation.- 9.3 Statistics of Optical Preamplification with Perfect Inversion.- 9.4 Statistics of Optical Preamplification with Incomplete Inversion.- 9.5 Bit-Error Rate with Optical Preamplification.- 9.5.1 Narrow-Band Filter, Polarized Signal, and Noise.- 9.5.2 Broadband Filter, Unpolarized Signal.- 9.6 Negentropy and Information.- 9.7 The Noise Figure of Optical Amplifiers.- 9.8 Summary.- Problems.- Solutions.- 10. Solitons and Long-Distance Fiber Communications.- 10.1 The Nonlinear Schrodinger Equation.- 10.2 The First-Order Soliton.- 10.3 Properties of Solitons.- 10.4 Perturbation Theory of Solitons.- 10.5 Amplifier Noise and the Gordon-Haus Effect.- 10.6 Control Filters.- 10.7 Erbium-Doped Fiber Amplifiers and the Effect of Lumped Gain.- 10.8 Polarization.- 10.9 Continuum Generation by Soliton Perturbation.- 10.10 Summary.- Problems.- Solutions.- 11. Phase-Sensitive Amplification and Squeezing.- 11.1 Classical Analysis of Parametric Amplification.- 11.2 Quantum Analysis of Parametric Amplification.- 11.3 The Nondegenerate Parametric Amplifier as a Model of a Linear Phase-Insensitive Amplifier.- 11.4 Classical Analysis of Degenerate Parametric Amplifier.- 11.5 Quantum Analysis of Degenerate Parametric Amplifier.- 11.6 Squeezed Vacuum and Its Homodyne Detection.- 11.7 Phase Measurement with Squeezed Vacuum.- 11.8 The Laser Resonator Above Threshold.- 11.9 The Fluctuations of the Photon Number.- 11.10 The Schawlow-Townes Linewidth.- 11.11 Squeezed Radiation from an Ideal Laser.- 11.12 Summary.- Problems.- Solutions.- 12. Squeezing in Fibers.- 12.1 Quantization of Nonlinear Waveguide.- 12.2 The x Representation of Operators.- 12.3 The Quantized Equation of Motion of the Kerr Effect in the x Representation.- 12.4 Squeezing.- 12.5 Generation of Squeezed Vacuum with a Nonlinear Interferometer.- 12.6 Squeezing Experiment.- 12.7 Guided-Acoustic-Wave Brillouin Scattering.- 12.8 Phase Measurement Below the Shot Noise Level.- 12.9 Generation of Schrodinger Cat State via Kerr Effect.- 12.10 Summary.- Problems.- Solutions.- 13. Quantum Theory of Solitons and Squeezing.- 13.1 The Hamiltonian and Equations of Motion of a Dispersive Waveguide.- 13.2 The Quantized Nonlinear Schrodinger Equation and Its Linearization.- 13.3 Soliton Perturbations Projected by the Adjoint.- 13.4 Renormalization of the Soliton Operators.- 13.5 Measurement of Operators.- 13.6 Phase Measurement with Soliton-like Pulses.- 13.7 Soliton Squeezing in a Fiber.- 13.8 Summary.- Problems.- Solutions.- 14. Quantum Nondemolition Measurements and the "Collapse" of the Wave Function.- 14.1 General Properties of a QND Measurement.- 14.2 A QND Measurement of Photon Number.- 14.3 "Which Path" Experiment.- 14.4 The "Collapse" of the Density Matrix.- 14.5 Two Quantum Nondemolition Measurements in Cascade.- 14.6 The Schrodinger Cat Thought Experiment.- 14.7 Summary.- Problems.- Solutions.- Epilogue.- Appendices.- A.1 Phase Velocity and Group Velocity of a Gaussian Beam.- A.2 The Hermite Gaussians and Their Defining Equation.- A.2.1 The Defining Equation of Hermite Gaussians.- A.2.2 Orthogonality Property of Hermite Gaussian Modes.- A.2.3 The Generating Function and Convolutions of Hermite Gaussians.- A.3 Recursion Relations of Bessel Functions.- A.4 Brief Review of Statistical Function Theory.- A.5 The Different Normalizations of Field Amplitudes and of Annihilation Operators.- A.5.1 Normalization of Classical Field Amplitudes.- A.5.2 Normalization of Quantum Operators.- A.6 Two Alternative Expressions for the Nyquist Source.- A.7 Wave Functions and Operators in the n Representation.- A.8 Heisenberg's Uncertainty Principle.- A.9 The Quantized Open-Resonator Equations.- A.10 Density Matrix and Characteristic Functions.- A.10.1 Example 1. Density Matrix of Bose-Einstein State.- A.10.2 Example 2. Density Matrix of Coherent State.- A.11 Photon States and Beam Splitters.- A.12 The Baker-Hausdorff Theorem.- A.12.1 Theorem 1.- A.12.2 Theorem 2.- A.12.3 Matrix Form of Theorem 1.- A.12.4 Matrix Form of Theorem 2.- A.13 The Wigner Function of Position and Momentum.- A.14 The Spectrum of Non-Return-to-Zero Messages.- A.15 Various Transforms of Hyperbolic Secants.- A.16 The Noise Sources Derived from a Lossless Multiport with Suppressed Terminals.- A.17 The Noise Sources of an Active System Derived from Suppression of Ports.- A.19 The Heisenberg Equation in the Presence of Dispersion.- References.

1/f noise in carbon nanotubes

Abstract: The electrical noise characteristics of single-walled carbon nanotubes have been investigated. For all three cases of individual isolated nanotubes, thin films of interconnected nanotubes, and bulk nanotube mats, anomalously large bias-dependent 1/f noise is found. The noise magnitude greatly exceeds that commonly observed in metal films, carbon resistors, or even carbon fibers with comparable resistances. A single empirical expression describes the noise for all nanotube samples, suggesting a common noise-generating mechanism proportional only to the number of nanotubes in the conductor. We consider likely sources of the fluctuations, and consequences for electronic applications of nanotubes if the excessive noise cannot be suppressed.

Can detectability be improved by adding noise

Abstract: It is shown that under certain conditions the performance of a suboptimal detector may be improved by adding noise to the received data. The reasons for this counterintuitive result are explained and a computer simulation example given.

An analysis of the broadband noise scenario in powerline networks

Abstract: Opposite to many other communication channels the powerline channel does not represent an additive white Gaussian noise (AWGN) environment; in the frequency range from some hundred kilohertz up to 20 MHz it is mostly dominated by narrow-band interference and impulsive noise. After a basic classification of the different types of noise the properties of background noise and narrow-band interference are discussed. Spectral analysis and time domain analysis of impulse noise gives some figures of the power spectral density as well as distributions of L noise f , I impulse noise ; J , . . .

Probing entanglement and nonlocality of electrons in a double-dot via transport and noise.

Abstract: Addressing the feasibility of quantum communication with electrons we consider entangled spin states of electrons in a double-dot which is weakly coupled to leads. We show that the entanglement of two electrons in the double-dot can be detected in mesoscopic transport and noise measurements. In the Coulomb blockade and cotunneling regime the singlet and triplet states lead to phase-coherent current and noise contributions of opposite signs and to Aharonov-Bohm and Berry phase oscillations. These oscillations are a genuine two-particle effect and provide a direct measure of nonlocality in entangled states. We show that the ratio of zero-frequency noise to current is equal to the electron charge.

Evaluating the error probability in lightwave systems with chromatic dispersion, arbitrary pulse shape and pre- and postdetection filtering

Abstract: A novel approach to analytically evaluate the bit error probability in optically preamplified direct-detection systems is presented, which can take into account the effects of pulse shaping, chirping, filtering at the transmitter and the receiver, both pre- and postdetection, chromatic dispersion, and ASE noise. The method is computationally very fast in that the saddle point integration method for solving the resulting line integral of a particular moment generating function is adopted. A closed-form approximation for the bit error probability is also provided, which is within 0.01 dB from the exact numerical results.

Strategies to improve the signal and noise performance of active matrix, flat‐panel imagers for diagnostic x‐ray applications

Abstract: A theoretical investigation of factors limiting the detective quantum efficiency (DQE) of active matrix flat-panel imagers (AMFPIs), and of methods to overcome these limitations, is reported. At the higher exposure levels associated with radiography, the present generation of AMFPIs is capable of exhibiting DQE performance equivalent, or superior, to that of existing film-screen and computed radiography systems. However, at exposure levels commonly encountered in fluoroscopy, AMFPIs exhibit significantly reduced DQE and this problem is accentuated at higher spatial frequencies. The problem applies both to AMFPIs that rely on indirect detection as well as direct detection of the incident radiation. This reduced performance derives from the relatively large magnitude of the square of the total additive noise compared to the system gain for existing AMFPIs. In order to circumvent these restrictions, a variety of strategies to decrease additive noise and enhance system gain are proposed. Additive noise could be reduced through improved preamplifier, pixel and array design, including the incorporation of compensation lines to sample external line noise. System gain could be enhanced through the use of continuous photodiodes, pixel amplifiers, or higher gain x-ray converters such as lead iodide. The feasibility of these and other strategies is discussed and potential improvements to DQE performance are quantified through a theoretical investigation of a variety of hypothetical 200 μm pitch designs. At low exposures, such improvements could greatly increase the magnitude of the low spatial frequency component of the DQE, rendering it practically independent of exposure while simultaneously reducing the falloff in DQE at higher spatial frequencies. Furthermore, such noise reduction and gain enhancement could lead to the development of AMFPIs with high DQE performance which are capable of providing both high resolution radiographicimages, at ∼100 μm pixel resolution, as well as variable resolution fluoroscopic images at 30 fps.

Experimental evidence of coherence resonance in an optical system

Abstract: Experimental evidence of coherence resonance in an optical system is reported. We show that the regularity of the excitable pulses in the intensity of a laser diode with optical feedback increases when adding noise, up to an optimal value of the noise strength. Both phase and amplitude fluctuations of the pulses play a relevant role in the dynamics of the system. We introduce the joint entropy of the two variables to generalize the indicator of coherence, and we put in evidence the mechanism of destruction of the excitable orbit after the resonance.

Noise in Integrate-and-Fire Neurons: From Stochastic Input to Escape Rates

Abstract: We analyze the effect of noise in integrate-and-fire neurons driven by time-dependent input and compare the diffusion approximation for the membrane potential to escape noise. It is shown that for time-dependent subthreshold input, diffusive noise can be replaced by escape noise with a hazard function that has a gaussian dependence on the distance between the (noise-free) membrane voltage and threshold. The approximation is improved if we add to the hazard function a probability current proportional to the derivative of the voltage. Stochastic resonance in response to periodic input occurs in both noise models and exhibits similar characteristics.

Reduction of mode partition noise by using semiconductor optical amplifiers

Abstract: Multi-wavelength light sources by narrow-band spectral filtering of multi-mode lasers have been studied for wavelength division multiplexing (WDM) applications. Long-wavelength Fabry-Perot (FP) semiconductor lasers provide many modes, whose mode spacing can be fixed with precise frequency by using a mode locking technique. However, increased intensity noise has been observed in the spectral filtering of multi-modes generated by mode-locked semiconductor lasers. This is known as mode partition noise. The noise appears as an extreme increase in the relative intensity noise (RIN) spectrum in low frequency regions. This limits transmission applications because of degradation of signal to noise ratio (SNR). In the paper, we demonstrate reduction of the mode partition noise by using a semiconductor optical amplifier (SOA). 16-dB SNR recovery is reported for spectral filtering of FP lasers.

Using capacitive cross-coupling technique in RF low noise amplifiers and down-conversion mixer design

Abstract: We report an approach to improve the noise performance of RF low noise amplifiers (LNAs) and down-conversion mixers. The technique we described here is based on capacitive cross-coupling across the two sides of a differential input stage. A LNA and mixer have been implemented in 0.5µ CMOS process to demonstrate the viability of this technique. The measurements show that the LNA achieves 3.0dB noise figure and 12.2 dB voltage gain (optimized for the maximum power transfer), and the mixer has 5.2dB DSB noise figure and 13.2 dB voltage conversion gain. Both LNA and mixer operate at 2.7V voltage supply and consume 27mW and 8.1mW power, respectively.

Noise of entangled electrons: Bunching and antibunching

Abstract: Addressing the feasibility of quantum communication with entangled electrons in an interacting many-body environment, we propose an interference experiment using a scattering setup with an entangler and a beam splitter. It is shown that, due to electron-electron interaction, the spin correlation of the entangled singlet and triplet states is reduced by z(F)(2) in a conductor described by Fermi liquid theory. We calculate the quasiparticle weight factor z(F) for a two-dimensional electron system. The current noise for electronic singlet states turns out to be enhanced (bunching behavior), while it is reduced for triplet states (antibunching). Within standard scattering theory, we find that the Fano factor (noise-to-current ratio) for singlets is twice as large as for independent classical particles and is reduced to zero for triplets.

High-repetition-rate optical pulse generation using a rational harmonic mode-locked fiber laser

Abstract: Rational harmonic mode locking takes place in an actively mode-locked fiber laser when the modulation frequency f/sub m/=(n+1/p)f/sub c/, where n and p are both integers and f/sub c/ is the inverse of the cavity round-trip time, the 22nd order of rational harmonic mode locking has been observed when f/sub m//spl ap/1 GHz. An optical pulse train with a repetition rate of 40 GHz has been obtained using a modulation frequency f/sub m/=10 GHz. The theory of rational harmonic mode locking has also been developed. The stability of the mode-locked pulses is improved considerably when a semiconductor optical amplifier is incorporated into the fiber laser cavity. The supermode noise in the RF spectrum of a mode-locked laser is removed for a certain range of current in the semiconductor optical amplifier.

Coherence resonance and noise-induced synchronization in globally coupled Hodgkin-Huxley neurons

Abstract: The coherence resonance (CR) of globally coupled Hodgkin-Huxley neurons is studied. When the neurons are set in the subthreshold regime near the firing threshold, the additive noise induces limit cycles. The coherence of the system is optimized by the noise. The coupling of the network can enhance CR in two different ways. In particular, when the coupling is strong enough, the synchronization of the system is induced and optimized by the noise. This synchronization leads to a high and wide plateau in the local CR curve. A bell-shaped curve is found for the peak height of power spectra of the spike train, being significantly different from a monotonic behavior for the single neuron. The local-noise-induced limit cycle can evolve to a refined spatiotemporal order through the dynamical optimization among the autonomous oscillation of an individual neuron, the coupling of the network, and the local noise.

RF-CMOS Performance Trends

Abstract: The impact of scaling on the analog performance of MOS devices at RF frequencies was studied. Trends in the RF performance of nominal gate length NMOS devices from 350-nm to 50-nm CMOS technologies are presented. Both experimental data and circuit simulations with an advanced validated compact model (MOS Model 11) have been used to evaluate the RF performance. RF performance metrics such as the cutoff frequency, maximum oscillation frequency, power gain, noise figure, linearity, and 1 noise were included in the analysis. The focus of the study was on gate and drain bias conditions relevant for RF circuit design. A scaling methodology for RF-CMOS based on limited linearity degradation is proposed.

Stochastic resonance in a bistable system subject to multiplicative and additive noise

Abstract: The stochastic resonance (SR) phenomenon in a bistable system under the simultaneous action of multiplicative and additive noise and periodic signal is studied by using the theory of signal-to-noise ratio (SNR) in the adiabatic limit. Two cases have been considered: the case of no correlations between multiplicative and additive noise and the case of correlations between two noises. The expressions of the SNR for both cases are obtained. The effects of intensity of multiplicative and additive noise and the intensity of the correlations between noises on the SNR are discussed for both cases, respectively. It is found that the existence of a maximum in the SNR is the identifying characteristic of the SR phenomenon. In the case of no correlations between multiplicative and additive noise, the SNR is independent of the initial condition of the system. However, the SNR is not only dependent on the intensity of correlations between noises, but also on the initial condition of the system in the presence of correlations between two noises.

Thermoelastic noise and homogeneous thermal noise in finite sized gravitational-wave test masses

Abstract: An analysis is given of thermoelastic noise (thermal noise due to thermoelastic dissipation) in finite sized test masses of laser interferometer gravitational-wave detectors. Finite-size effects increase the thermoelastic noise by a modest amount; for example, for the sapphire test masses tentatively planned for LIGO-II and plausible beam-spot radii, the increase is ≲10 percent. As a side issue, errors are pointed out in the currently used formulas for conventional, homogeneous thermal noise (noise associated with dissipation which is homogeneous and described by an imaginary part of the Young’s modulus) in finite sized test masses. Correction of these errors increases the homogeneous thermal noise by ≲5 percent for LIGO-II-type configurations.

A laser-locked cavity ring-down spectrometer employing an analog detection scheme

Abstract: A system is described that employs a diode-pumped Nd:YAG continuous-wave laser source servolocked to a three-mirror optical cavity and an analog detection circuit that extracts the ring-down rate from the exponentially decaying ring-down waveform. This scheme improves on traditional cavity ring-down spectroscopy setups by increasing signal acquisition rates to tens of kilohertz and reducing measurement noise sources. For example, an absorption spectrum of a weak CO2 transition at 1064 nm is obtained in less than 10 s at a spectral resolution of 75 kHz employing a cavity with an empty-cavity ring-down decay lifetime of 2.8 μs and a total roundtrip path length of 42 cm. The analog detection system enables laser frequency scan rates greater than 500 MHz/s. The long-term sensitivity of this system is 8.8×10−12 cm−1 Hz−1/2 and the short-term sensitivity is 1.0×10−12 cm−1 Hz−1/2.

Subthreshold voltage noise due to channel fluctuations in active neuronal membranes.

Abstract: Voltage-gated ion channels in neuronal membranes fluctuate randomly between different conformational states due to thermal agitation. Fluctuations between conducting and nonconducting states give rise to noisy membrane currents and subthreshold voltage fluctuations and may contribute to variability in spike timing. Here we study subthreshold voltage fluctuations due to active voltage-gated Na+ and K+ channels as predicted by two commonly used kinetic schemes: the Mainen et al. (1995) (MJHS) kinetic scheme, which has been used to model dendritic channels in cortical neurons, and the classical Hodgkin-Huxley (1952) (HH) kinetic scheme for the squid giant axon. We compute the magnitudes, amplitude distributions, and power spectral densities of the voltage noise in isopotential membrane patches predicted by these kinetic schemes. For both schemes, noise magnitudes increase rapidly with depolarization from rest. Noise is larger for smaller patch areas but is smaller for increased model temperatures. We contrast the results from Monte Carlo simulations of the stochastic nonlinear kinetic schemes with analytical, closed-form expressions derived using passive and quasi-active linear approximations to the kinetic schemes. For all subthreshold voltage ranges, the quasi-active linearized approximation is accurate within 8% and may thus be used in large-scale simulations of realistic neuronal geometries.

Examining Noise Sources at the Single-Molecule Level: 1 / f Noise of an Open Maltoporin Channel

Abstract: We have studied the phenomenological origin of $1/f$ noise in a solute-specific bacterial ion channel, maltoporin. We show that after excision of small, but resolvable stepwise changes in the recordings of the current through a single open channel, the $1/f$ noise component disappears and the channel exhibits noise that is ``white'' below 100 Hz. Combined with results of a recent noise study of several bacterial porins, our observations suggest that $1/f$ noise is caused by the equilibrium conductance fluctuations related to the conformational flexibility of the channel pore structural constituents.

Direct strain estimation in elastography using spectral cross-correlation.

Abstract: Spectral estimation of tissue strain has been performed previously by using the centroid shift of the power spectrum or by estimating the variation in the mean scatterer spacing in the spectral domain. The centroid shift method illustrates the robustness of the direct, incoherent strain estimator. In this paper, we present a strain estimator that uses spectral cross-correlation of the pre- and postcompression power spectrum. The centroid shift estimator estimates strain from the mean center frequency shift, while the spectral cross-correlation estimates the shift over the entire spectrum. Spectral cross-correlation is shown to be more sensitive to small shifts in the power spectrum and, thus, provides better estimation for smaller strains when compared to the spectral centroid shift. Spectral cross-correlation shares all the advantages gained using the spectral centroid shift, in addition to providing accurate and precise strain estimation for small strains. The variance and noise properties of the spectral strain estimators quantified by their respective strain filters are also presented.