Showing papers on "Noise measurement published in 2000"

Noise in RF-CMOS mixers: a simple physical model

Abstract: Flicker noise in the mixer of a zero- or low-intermediate frequency (IF) wireless receiver can compromise overall receiver sensitivity. A qualitative physical model has been developed to explain the mechanisms responsible for flicker noise in mixers. The model simply explains how frequency translations take place within a mixer. Although developed to explain flicker noise, the model predicts white noise as well. Simple equations are derived to estimate the flicker and white noise at the output of a switching active mixer. Measurements and simulations validate the accuracy of the predictions, and the dependence of mixer noise on local oscillator (LO) amplitude and other circuit parameters.

Quantile based noise estimation for spectral subtraction and Wiener filtering

Abstract: Elimination of additive noise from a speech signal is a fundamental problem in audio signal processing. In this paper we restrict our considerations to the case where only a single microphone recording of the noisy signal is available. The algorithms which we investigate proceed in two steps. First, the noise power spectrum is estimated. A method based on temporal quantiles in the power spectral domain is proposed and compared with pause detection and recursive averaging. The second step is to eliminate the estimated noise from the observed signal by spectral subtraction or Wiener filtering. The database used in the experiments comprises 6034 utterances of German digits and digit strings by 770 speakers in 10 different cars. Without noise reduction, we obtain an error rate of 11.7%. Quantile based noise estimation and Wiener filtering reduce the error rate to 8.6%. Similar improvements are achieved in an experiment with artificial, non-stationary noise.

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.

Maximum-likelihood array processing in non-Gaussian noise with Gaussian mixtures

Abstract: Many approaches have been studied for the array processing problem when the additive noise is modeled with a Gaussian distribution, but these schemes typically perform poorly when the noise is non-Gaussian and/or impulsive. This paper is concerned with maximum likelihood array processing in non-Gaussian noise. We present the Cramer-Rao bound on the variance of angle-of-arrival estimates for arbitrary additive, independent, identically distributed (iid), symmetric, non-Gaussian noise. Then, we focus on non-Gaussian noise modeling with a finite Gaussian mixture distribution, which is capable of representing a broad class of non-Gaussian distributions that include heavy tailed, impulsive cases arising in wireless communications and other applications. Based on the Gaussian mixture model, we develop an expectation-maximization (EM) algorithm for estimating the source locations, the signal waveforms, and the noise distribution parameters. The important problems of detecting the number of sources and obtaining initial parameter estimates for the iterative EM algorithm are discussed in detail. The initialization procedure by itself is an effective algorithm for array processing in impulsive noise. Novel features of the EM algorithm and the associated maximum likelihood formulation include a nonlinear beamformer that separates multiple source signals in non-Gaussian noise and a robust covariance matrix estimate that suppresses impulsive noise while also performing a model-based interpolation to restore the low-rank signal subspace. The EM approach yields improvement over initial robust estimates and is valid for a wide SNR range. The results are also robust to PDF model mismatch and work well with infinite variance cases such as the symmetric stable distributions. Simulations confirm the optimality of the EM estimation procedure in a variety of cases, including a multiuser communications scenario. We also compare with existing array processing algorithms for non-Gaussian noise.

Signal/noise KLT based approach for enhancing speech degraded by colored noise

Abstract: A signal/noise Karhunen-Loeve transform (KLT) based approach for enhancing speech degraded by colored noise is proposed. The noisy speech frames are classified into speech-dominated frames and noise-dominated frames. In the speech-dominated frames, the signal KLT matrix is used and in the noise dominated frames, the noise KLT matrix is used. The approach does not require noise whitening and hence works well even with narrowband noise. A two-dimensional objective measure which captures both the speech distortion and the noise shaping characteristics of the algorithm is proposed. This measure indicates that the proposed method performs better noise shaping than a modified form of the signal subspace approach proposed by Ephraim and Van Trees (1995) and the standard spectral subtraction method. Informal listening tests show that the proposed algorithm does not suffer from the problem of residual musical noise and performs better noise masking than the signal subspace approach.

De-noising by modified soft-thresholding

Abstract: Based on the soft-thresholding, a new noise smoother is introduced in this letter. Since a new statistics is used to make the estimation, the proposed algorithm can smooth both white and impulsive noise efficiently.

Robust voice activity detection algorithm for estimating noise spectrum

Abstract: A new voice activity detection (VAD) algorithm is proposed for estimating the spectrum of car noise in which noise is filtered out in the frequency domain. The proposed algorithm uses the log energy parameters which are composed of two parts in the critical band. The algorithm detects the noise period by applying two adaptive thresholds to each part. Using the noise period we can reliably estimate the time-varying noise characteristics. The advantage of the proposed technique is that it can prevent incorrect detections caused by unvoiced or nasal sounds with high frequency components being covered by car noise with low frequency components. The algorithm is suitable for real time implementation with one microphone. Also, a speaker independent speech recognition system has been implemented for car navigation using a fixed point Oak DSP system, which incorporates the proposed VAD algorithm. The system enhanced the recognition rates for 12 isolated command words to 94.52%, compared with the 80.7% of the baseline recogniser.

System and method for dual microphone signal noise reduction using spectral subtraction

Abstract: Speech enhancement is provided in dual microphone noise reduction systems by including spectral subtraction algorithms using linear convolution, causal filtering and/or spectrum dependent exponential averaging of the spectral subtraction gain function. According to exemplary embodiments, when a far-mouth microphone is used in conjunction with a near-mouth microphone, it is possible to handle non-stationary background noise as long as the noise spectrum can continuously be estimated from a single block of input samples. The far-mouth microphone, in addition to picking up the background noise, also picks up the speaker's voice, albeit at a lower level than the near-mouth microphone. To enhance the noise estimate, a spectral subtraction stage is used to suppress the speech in the far-mouth microphone signal. To be able to enhance the noise estimate, a rough speech estimate is formed with another spectral subtraction stage from the near-mouth signal. Finally, a third spectral subtraction function is used to enhance the near-mouth signal by suppressing the background noise using the enhanced background noise estimate.

Analysis and experimental verification of digital substrate noise generation for epi-type substrates

Abstract: Substrate coupling in mixed-signal IC's can cause important performance degradation of the analog circuits Accurate simulation is therefore needed to investigate the generation, propagation, and impact of substrate noise Recent studies were limited to the time-domain behavior of generated substrate noise and to noise injection from a single noise source This paper focuses on substrate noise generation by digital circuits and on the spectral content of this noise To simulate the noise generation, a SPICE substrate model for heavily doped epi-type substrates has been used The accuracy of this model has been verified with measurements of substrate noise, using a wide-band, continuous-time substrate noise sensor, which allows accurate measurement of the spectral content of substrate noise The substrate noise generation of digital circuits is analyzed, both in the time and frequency domain, and the influence of the different substrate noise coupling mechanisms is demonstrated It is shown that substrate noise voltages up to 20 mV are generated and that, in the frequency band up to 1 GHz, noise peaks are generated at multiples of the clock and repetition frequency These noise signals will strongly deteriorate the behavior of small signal analog amplifiers, as used in integrated front-ends

Removal of fixed pattern noise and other fixed patterns from media signals

Abstract: A method of removing fixed pattern noise derives an estimate of fixed pattern noise from a composite media signal and uses the estimate to evaluate and remove fixed pattern noise from selected frames. The technique is particularly suited for removing fixed pattern noise in images due to image capture processes, but applies to other media signals as well. In watermarking applications, the method can be used to improve detection and recovery of a watermark. Also, it may be used to remove components of a watermark or a watermark from a cover signal that contains two or more different watermarks.

A 2-GHz low-phase-noise integrated LC-VCO set with flicker-noise upconversion minimization

Abstract: A fully integrated 2-GHz very low-phase-noise LC-tank voltage-controlled oscillator (VCO) set with flicker noise upconversion minimization is presented. Using only integrated planar inductors, the measured phase noise is as low as -125.1 dBc/Hz at 600-kHz offset and -138 dBc/Hz at 3 MHz. The excellent phase-noise performance is achieved by means of an in-house-developed integrated inductor simulator optimizer. To minimize the upconversion of flicker noise to 1/f/sup 3/ phase noise, a flicker-noise upconversion factor is defined, which can easily be extracted from circuit simulation. The technique is applied to demonstrate the relationship between the flicker-noise upconversion and the overdrive level of the oscillators' MOS cross-coupled pair and to develop circuit balancing techniques to even further reduce the flicker-noise upconversion. The 1/f/sup 3/ phase-noise corner is minimized to be less than 15 kHz. The VCO's are implemented in a three-metal layer, 0.65-/spl mu/m BiCMOS process, using only MOS active devices.

Subsonic Jet Noise from Nonaxisymmetric and Tabbed Nozzles

Abstract: Subsonic jet noise from nonaxisymmetric and tabbed nozzles are investigated experimentally and theoretically. It is shown that the noise spectra of these jets are in good agreement with the similarity spectra found empirically earlier by Tam et al. through a detailed analysis of supersonic jet noise data (Tam, C. K. W., Golebiowski, M., and Seiner, J. M., On the Two Components of Turbulent Mixing Noise from Supersonic Jets, AIAA Paper 96-1716, 1996). Furthermore, the radiated noise fields of the jets under study, including elliptic and large-aspect-ratio rectangular jets, are found to be quite axisymmetric and are practically the same as that of a circular jet with the same exit area. These experimental results strongly suggest that nozzle geometry modification into elliptic or rectangular shapes is not an effective method for jet noise suppression. A lobed nozzle, on the other hand, is found to impact significantly the noise field. Noise from large-scale turbulent structures, radiating principally in the downstream direction, is effectively suppressed. Tabs also impact the noise field, primarily by shifting the spectral peak to a higher frequency. A jetlets model is developed to provide a basic understanding of the noise from tabbed jets. The model predicts that the noise spectrum from a jet with N tabs (N ≥ 2) can he obtained from that of the original jet (no tab) by a simple frequency shift. The shifted frequency is obtained by multiplying the original frequency by N 1/2 . This result is in fairly good agreement with experimental data.

Adaptive digital correction of analog errors in MASH ADCs. II. Correction using test-signal injection

Abstract: For pt. I see ibid., vol. 47, no. 7, p. 621-8 (2000). This part describes a different adaptation strategy. It relies on the injection of a pseudorandom two-level test signal at the input of the first-stage quantizer, where it is added to the quantization noise. The test signal then leaks into the output signal, where it can be detected and used to control the digital noise-cancellation filter. This paper describes the correction process, as well as some efficient structures for implementing it, and demonstrates the effectiveness of the technique by describing three design examples.

Impact of the beat noise on the performance of 2-D optical CDMA systems

Abstract: The system performance of 2-D wavelength hopping/time spreading CDMA systems is found to be limited by the occurrence of the beat noise between the components of the signal and the multiple user interference. The variance of the noise is determined and the probability of error is calculated for a general system employing asymmetric prime-hop sequences. A comparison with an idealized system neglecting the beat noise reveals that the system performance is seriously affected by the beat noise.

Noise in mixers, oscillators, samplers, and logic an introduction to cyclostationary noise

Abstract: The proliferation of wireless and mobile products has dramatically increased the number and variety of low power, high performance electronic systems being designed. Noise is an important limiting factor in these systems. The noise generated is often cyclostationary. This type of noise cannot be predicted using SPICE, nor is it well handled by traditional test equipment such as spectrum analyzers or noise figure meters, but it is available from the new RF simulators. The origins and characteristics of cyclostationary noise are described in a way that allows designers to understand the impact of cyclostationarity on their circuits. In particular, cyclostationary noise in time-varying systems (mixers), sampling systems (switched filters and sample/holds), thresholding systems (logic circuitry), and autonomous systems (oscillators) is discussed.

Automatic sound detection and recognition for noisy environment

Abstract: This paper addresses the problem of automatic detection and recognition of impulsive sounds, such as glass breaks, human screams, gunshots, explosions or door slams. A complete detection and recognition system is described and evaluated on a sound database containing more than 800 signals distributed among six different classes. Emphasis is set on robust techniques, allowing the use of this system in a noisy environment. The detection algorithm, based on a median filter, features a highly robust performance even under important background noise conditions. In the recognition stage, two statistical classifiers are compared, using Gaussian Mixture Models (GMM) and Hidden Markov Models (HMM), respectively. It can be shown that a rather good recognition rate (98% at 70dB and above 80% for 0dB signal-to-noise ratios) can be reached, even under severe gaussian white noise degradations.

Noise reduction apparatus and method

Abstract: A multi-band spectral subtraction scheme is proposed, comprising a multi-band filter architecture, noise and signal power detection, and gain function for noise reduction. In one embodiment, the gain function for noise reduction consists of a gain scale function and a maximum attenuation function providing a predetermined amount of gain as a function of signal to noise ratio (“SNR”) and noise. In one embodiment, the gain scale function is a three-segment piecewise linear function, and the three piecewise linear sections of the gain scale function include a first section providing maximum expansion up to a first knee point for maximum noise reduction, a second section providing less expansion up to a second knee point for less noise reduction, and a third section providing minimum or no expansion for input signals with high SNR to minimize distortion. According to embodiments of the present invention, the maximum attenuation function can either be a constant or equal to the estimated noise envelope. The disclosed noise reduction techniques can be applied to a variety of speech communication systems, such as hearing aids, public address systems, teleconference systems, voice control systems, or speaker phones. When used in hearing aid applications, the noise reduction gain function according to aspects of the present invention is combined with the hearing loss compensation gain function inherent to hearing aid processing.

Power and noise limitations of active circulators

Abstract: In this paper, new simple formulas expressing the power and noise limitations for three three-way circulator architectures and three quasi-circulator architectures are derived. It is shown that the power-handling capability of the active three-way circulators is determined by the required transconductance of the transistors in the circuit, while the noise is determined by the drain noise current source. The suitability of the different active circulator architectures for transmit/receive applications is investigated, We conclude that the quasi-circulators based on passive isolation offer the highest performance.

Using the Allan variance and power spectral density to characterize dc nanovoltmeters

Abstract: When analyzing nanovoltmeter measurements, stochastic serial correlations are often ignored and the experimental standard deviation of the mean is assumed to be the experimental standard deviation of a single observation divided by the square root of the number of observations. This is justified only for white noise. This paper demonstrates the use of the power spectrum and the Allan variance to analyze data, identify the regimes of white noise, and characterize the performance of digital and analog DC nanovoltmeters. Limits imposed by temperature variations, 1/f noise and source resistance are investigated.

Normalization of local contrast in mammograms

Abstract: Equalizing image noise has been shown to be an important step in automatic detection of microcalcifications in digital mammograms. In this study, an accurate adaptive approach for noise equalization is presented and investigated. No additional information obtained from phantom recordings is improved in the method, which makes the approach robust and independent of film type and film development characteristics. Furthermore, it is possible to apply the method on direct digital mammograms as well. In this study, the adaptive approach is optimized by investigating a number of alternative approaches to estimate the image noise. The estimation of high-frequency noise as a function of the grayscale is improved by a new technique for dividing the grayscale in sample intervals and by using a model for additive high-frequency noise. It is shown that the adaptive noise equalization gives substantially better detection results than does a fixed noise equalization. A large database of 245 digitized mammograms with 341 clusters was used for evaluation of the method.

Wavelet-based noise removal for biomechanical signals: a comparative study

Abstract: The purpose of this paper is to present wavelet-based noise removal (WBNR) techniques to remove noise from biomechanical acceleration signals obtained from numerical differentiation of displacement data. Manual and semiautomatic methods were used to determine thresholds for both orthogonal and biorthogonal filters. This study also compares the performance of WBNR approaches with four automatic conventional noise removal techniques used in biomechanics. The conclusion of this work is that WBNR techniques are very effective in removing noise from differentiated signals with sharp transients while leaving these transients intact. For biomechanical signals with certain characteristics, WBNR techniques perform better than conventional methods, as indicated by quantitative merit measures.

Low-frequency noise measurements as a characterization tool for degradation phenomena in solid-state devices

Abstract: The analysis of the degradation mechanisms that affect solid-state devices represents a key factor in the era of VLSI technology. This paper presents an overview of how the low-frequency noise measurement (LFNM) technique has been applied to the study of the most frequent causes of failure in integrated circuits and discrete components. After discussing noise and fluctuations in electron devices, we present some results obtained by applying LFNM to the analysis of some degradation mechanisms. Although several other causes of degradation are taken into consideration (ageing, radiation, hot electrons), the focus is on two specific failure mechanisms: electromigration in interconnect lines and ultra-thin oxide breakdown in MOS capacitors. Experience has highlighted the need for dedicated measurement systems, thus an entire section of the paper outlines both the instrumentation required and the reduction of the effects of spurious noise sources and external disturbances.

Time exposure acoustics

Abstract: An analysis of a passive seismic method for subsurface imaging is presented, in which ambient seismic noise is employed as the source of illumination of underground scatterers. The imaging algorithm can incorporate new data into the image in a recursive fashion, which causes image background noise to diminish over time. Under the assumption of spatially-incoherent ambient noise, an analytical expression for the point-spread function of the imaging algorithm is derived. The point-spread function (PDF) characterizes the resolution of the image, which is a function of the receiving array length and the ambient noise bandwidth. Results of a Monte Carlo simulation are presented to illustrate the theory.

Measurements and analyses of substrate noise waveform in mixed-signal IC environment

Abstract: A transition-controllable noise source is developed in a 0.1-/spl mu/m P-substrate N-well CMOS technology. This noise source can generate substrate noises with controlled transitions in size, interstage delay and direction for experimental studies on substrate noise properties in a mixed-signal integrated circuit environment. Substrate noise measurements of 100 ps, 100-/spl mu/s resolution are performed by indirect sensing that uses the threshold voltage shift in a latch comparator and by direct probing that uses a PMOS source follower. Measured waveforms indicate that peaks reflecting logic transition frequencies have a time constant that is more than ten times larger than the switching time. Analyses with equivalent circuits confirm that charge transfer between the entire parasitic capacitance in digital circuits and an external supply through parasitic impedance to supply/return paths dominates the process, and the resultant return bounce appears as the substrate noise.

MOSFET 1/f noise measurement under switched bias conditions

Abstract: A new measurement setup is presented that allows the observation of 1/f noise spectra in MOSFET's under switched bias conditions in a wide frequency band (10 Hz-100 kHz). When switching between inversion and accumulation, MOSFET's of different manufacturers invariably show reduced 1/f noise power density for frequencies below the switching frequency. At low frequencies (10 Hz), a 5-8 dB reduction in intrinsic 1/f noise power density is found for different devices, largely independent of the switching frequency (up to 1 MHz). The switched bias measurements render detailed wideband 1/f noise spectra of switched MOSFET's, which is useful for 1/f noise model validation and analog circuit design.

Detecting independent motion: the statistics of temporal continuity

Abstract: We consider a problem central in aerial visual surveillance applications; detection and tracking of small, independently moving objects in long and noisy video sequences. We directly use spatiotemporal image intensity gradient measurements to compute an exact model of background motion. This allows the creation of accurate mosaics over many frames, and the definition of a constraint violation function which acts as an indicator of independent motion. A novel temporal integration method maintains confidence measures over long subsequences without computing the optic flow, requiring object models, or using a Kalman filter. The mosaic acts as a stable feature frame, allowing precise localization of the independently moving objects. We present a statistical analysis of the effects of image noise on the constraint violation measure and find a good match between the predicted probability distribution function and the measured sample frequencies in a test sequence.

An algorithm for integrated noise reduction and sharpness enhancement

Abstract: Noise reduction and image sharpening are techniques to improve video image quality. However, noise filters tend to blur image detail, while filters for image sharpening tend to increase noise. So, cascading the two filters does not always give the best performance. We present an integrated filter that reduces noise and sharpens details in a noisy video signal depending on local image statistics. This allows both features to be maximally exploited.

Avalanche noise measurement in thin Si p+-i-n+ diodes

Abstract: The avalanche multiplication and excess noise properties of a range of submicron Si diodes have been investigated. In these thin diodes the excess noise is found to fall below that predicted by conventional local noise theory. Modeling of the multiplication and excess noise using a recurrence method, which includes the dead space for carrier ionization, gives good agreement with experiment. This suggests that the dead space can reduce the excess noise in submicron Si diodes.

Adaptive noise energy estimation in pathological speech signals

Abstract: For pathological voices, spectral noise is closely related to the degree of perceived hoarseness. In this paper, noise variations are tracked during an utterance by means of an adaptive version of the normalized noise energy method (H. Kasuya et al., J. Acoust. Soc. Amer., vol. 80, no. 5, p. 1329-34, 1986). A first step is devoted to pitch estimation, which allows defining the varying optimal time window length for noise retrieval, avoiding empty "dip" regions. The approach Is tested on synthetic data and applied to real data coming from cordectomised adult male patients.