Showing papers on "Noise measurement published in 1990"

Characterization of single channel currents using digital signal processing techniques based on Hidden Markov Models.

Abstract: Techniques for extracting small, single channel ion currents from background noise are described and tested. It is assumed that single channel currents are generated by a first-order, finite-state, discrete-time, Markov process to which is added `white' background noise from the recording apparatus (electrode, amplifiers, etc.). Given the observations and the statistics of the background noise, the techniques described here yield a posteriori estimates of the most likely signal statistics, including the Markov model state transition probabilities, duration (open- and closed-time) probabilities, histograms, signal levels, and the most likely state sequence. Using variations of several algorithms previously developed for solving digital estimation problems, we have demonstrated that: (1) artificial, small, first-order, finite-state, Markov model signals embedded in simulated noise can be extracted with a high degree of accuracy, (2) processing can detect signals that do not conform to a first-order Markov model but the method is less accurate when the background noise is not white, and (3) the techniques can be used to extract from the baseline noise single channel currents in neuronal membranes. Some studies have been included to test the validity of assuming a first-order Markov model for biological signals. This method can be used to obtain directly from digitized data, channel characteristics such as amplitude distributions, transition matrices and open- and closed-time durations.

Detection of non-Gaussian signals in non-Gaussian noise using the bispectrum

Abstract: The problem of detecting a non-Gaussian time series in the presence of additive Gaussian or non-Gaussian noise is cast into a classical hypothesis testing framework, using the sample bispectrum as the test statistic The power of the test is demonstrated as a function of signal-to-noise ratio, the degree of skewness of the signal, and processing parameters The results are compared to the power of a classical energy detection test It is concluded that the bispectrum can be used effectively to detect non-Gaussian signals in the presence of interfering noise and that it may perform better, depending on the degree of non-Gaussianity, than energy detection >

Impact of phase noise in weakly coherent systems: a new and accurate approach

Abstract: Coherent optical systems for future broadband local loops may use lasers with significant phase noise, manifest as broad linewidths. This phase noise can be accommodated if the receiver is correctly designed, i.e. if nonsynchronous (envelope or square-law) IF demodulation is used and sufficient IF bandwidth is provided. It is difficult to analyze the performance of a coherent optical receiver when the signals are corrupted by phase noise. The central theoretical problem arising from filtering a signal with phase noise is defined in a particular form which permits the derivation of the forward or Fokker-Planck partial differential equation for probability density of the output voltage of the receiver. The results are used to discuss the IF bandwidth required for optical heterodyne receivers for amplitude-shift-keying (ASK) signals. >

Noise characteristics of Er/sup 3+/-doped fiber amplifiers pumped by 0.98 and 1.48 mu m laser diodes

Abstract: Measured noise characteristics of Er/sup 3+/-doped optical fiber amplifiers pumped by 0.98- and 1.48- mu m laser diodes (LDs) are reported. The noise figures estimated from the beat noise between signal and spontaneous emission are 3.2 dB for pumping by 0.98- mu m LD and 4.1 dB for pumping by 1.48- mu m LD. The beat noise between spontaneous emission components and the spontaneous shot noise for the 0.98- mu m pumping are lower than those for the 1.48- mu m pumping. >

Acoustic noise suppression using regressive adaptive filtering

Abstract: Experimental field tests dealing with the background acoustic noise in cars under various driving conditions are described. Analysis reveals that there is a high correlation between the acoustic noise in the area facing the driver's seat and the noise in other locations in the car, which suggests the possibility of using the two-microphones noise cancellation approach. Results show that using a conventional finite-impulse response adaptive filter with the stochastic gradient adaptation algorithm leads to up to 12 dB of noise cancellation in the low end of the noise spectrum; some noise enhancement was noticed at the high end of the spectrum. This problem is discussed, along with a possible solution approach using proper filtering. A limitation of the two-microphones cancellation is that the optimal location of the secondary microphone varies, depending on the driving conditions. A multiple secondary microphones scheme is proposed as a solution. This scheme resulted in further reductions of the residual noise. >

Low-frequency noise performance of self-aligned InAlAs/InGaAs heterojunction bipolar transistors

Abstract: The first measurement of low-frequency noise performance for self-aligned InAlAs/InGaAs HBTs is reported. The 1/f noise obtained was around 20 dB lower than that for AlGaAs/GaAs HBTs at a fixed frequency, which is considered to be caused by the low surface recombination velocity of InGaAs.

Noise analysis of linear microwave circuits

Abstract: The fundamentals of computer-aided noise analysis of linear noisy microwave circuits are presented. The method is based on the description of noisy networks by correlation matrices, and allows the noise analysis of linear circuits of general topology exhibiting arbitrary correlations between the noise sources. The description of linear noisy networks by correlation matrices in different representations, the interconnection of noisy networks and the nodal analysis of noisy networks are treated. The correlation matrices of circuits or subcircuits exhibiting thermal noise may be calculated directly from its admittance matrix. The application of the method for the noise analysis of linear microwave amplifiers is discussed.

Multiplicative noise models: parameter estimation using cumulants

Abstract: Develops algorithms based on higher-order moments and cumulants to estimate the parameters of a linear or harmonic process which is corrupted by multiplicative noise. The observations may be further corrupted by additive colored Gaussian noise. It is shown that parameter estimation is fairly easy when the multiplicative noise is i.i.d. and has nonzero mean. The colored Gaussian and zero-mean i.i.d. multiplicative noise cases are also considered. >

The complex cepstrum and bicepstrum: analytic performance evaluation in the presence of Gaussian noise

Abstract: An analytic performance evaluation of the complex cepstrum, power cepstrum, bicepstrum, and power bicepstrum is presented by providing approximate expressions of the bias and variance of the cepstrum parameters due to the presence of Gaussian noise. The approximations are based on the asymptotic properties of bispectrum estimates, and they are valid for moderate signal-to-noise ratios (SNRs). The assumed model consists of a deterministic signal (e.g. multiple echoes) in additive white Gaussian noise and finite length data. The validity of the analytic expressions is verified with Monte Carlo simulations. Performance comparisons between bicepstrum and cepstrum methods suggest that the improved performance of the bicepstrum is a function of SNR, A( omega ), M, and N. >

DBR active optical filters: transfer function and noise characteristics

Abstract: A theoretical model of distributed Bragg reflector (DBR) active filters is presented and verified experimentally through measurements of the transfer function and the noise spectra. The theory allows simple yet accurate evaluation of the transmission transfer function and of the noise properties of this class of filters. A conventional DBR laser device used as a filter is shown, experimentally and theoretically, to have two drawbacks: a multilobe transfer function and small gain (less than 10 dB facet-to-facet). It is shown how both problems can be overcome via reduction of two key device parameters: the grating coupling coefficient and the physical length of the active and/or phase control sections. This technique can lead to devices with attractive properties, having a gain of 35 dB, sidelobe suppression of 32 dB, and bandwidth as narrow as 1 GHz. >

Adaptive thresholding technique

Abstract: ADAPTIVE THRESHOLDING TECHNIQUE ABSTRACT OF THE DISCLOSURE An adaptive thresholding technique is calculated by using a real-time 16 pixel running average (RA) 18 to which is added an offset value. The offset value 38 is the product of a programmable factor (alpha) and a Sum Absolute Difference (SAD) noise measurement. The adaptive threshold 42 is compared by a comparator 48 with a delayed analog video signal intensity value on line 46 for the pixel associated with the adaptive threshold. The comparator 48 provides a binary video output for further processing. A relative video output may also be provided by taking the difference of the analog video signal 46 and its corresponding running average 18.

Deep-ocean vertical noise directionality

Abstract: The structure of beam noise measured at the output of a vertical array in a range dependent ocean basin was investigated using the modified wide-angle parabolic equation (PE). Noise sources were distributed throughout the basin, and the field due to each noise source at an array located in the midbasin was calculated. The response of the array to the superposition of the noise sources was found by beamforming. An efficient and direct approach that superimposes the noise sources on the PE field as the field is marched toward the array was developed. Downslope calculations of the midbasin vertical directionality were made between 50 and 400 Hz with this technique. Use of a geoacoustic model shows that the bottom behaves as a low-pass filter. >

Hough transform and signal detection theory performance for images with additive noise

Abstract: The line detection performance and sensitivity to the noise distribution of the Hough transform and two signal detection theory processors are evaluated quantitatively (using receiver operating characteristics (ROC)) and compared for images corrupted by each of several types of additive noise. The types of noise distributions considered are Gaussian, uniform, and Laplacian. The two types of signal detection theory processors considered are the optimal detector for additive, Gaussian noise and the optimal detector for additive, Laplacian noise. The performances for these noise distributions are interesting to compare because they vary widely in the thickness of the tails of their probability density functions. The Gaussian processor and the Hough transform are found to be much less sensitive to noise type than the Laplacian processor.

Pulsed noise in self-sustained oscillations of musical instruments

Abstract: A theory of bow and breath noise generation has been tested by analyzing recorded cello tones and by simulation using physical models of the cello and clarinet. For the synthesis to be successful, the listener's perceptions of noise and sound must fuse. Evidence is presented that the noise must be pulse modulated in a period synchronous way, as is shown for voiced fricatives. A method is described which is practical for enhancing naturalness of synthesis from physical models. No additional control parameters are required. Changes in the noise sound follow in a predictable way control changes in bowing, breath, and embouchure parameters in the simulations. >

Noise cancellation system

Abstract: This disclosure relates to a self-adaptive noise cancellation system that may be employed in a noise environment at the vicinity of an acoustic noise source to produce noise signals denoted as anti-noise signals that are directed towards a geometric region of the same environment and which counter the first acoustic noise source thus rendering the geometric region relatively quiet. The system monitors the acoustic noise source to identify its signal parameters thus retrieving the noise parameters that are required for the device to tune itself in order to cope with variations in the parameters of the noise source and to adapt its own anti-noise output to keep adequate noise cancellation in said geometric region in the face of the changes in the characteristics of the noise source, such as changes in power or in frequency spectrum of the noise source.

Frequency noise measurement of diode-pumped Nd:YAG ring lasers

Abstract: The combined frequency noise spectrum of two lightwave Model 120-01A nonplanar ring oscillator lasers was measured by first heterodyne detecting the IF signal and then measuring the IF frequency noise using an RF frequency discriminator. The results indicated the presence of a 1/f/sup 2/ noise component in the power spectral density of the frequency fluctuations between 1 Hz and 1 kHz. After incorporating this 1/f/sup 2/ into the analysis of the optical phase tracking loop, the measured phase error variance closely matches the theoretical predictions. >

Noise overshoot at drain current kink in SOI MOSFET

Abstract: The bias dependence of the drain current noise power of SOI (silicon-on-insulator) MOSFETs was studied, and low frequency noise overshoot at the drain current was observed. The overshoot has a width of about 0.7 V and exhibits a peak noise power which is two orders of magnitude higher than the normal noise level. The SOI devices used in this study were N-channel polysilicon gate MOSFETs on SIMOX (separation by implantation of oxygen) wafers fabricated with conventional submicron CMOS technology. The SOI film thickness, the buried-oxide thickness, and the gate oxide are 100 nm, 300 nm, and 11.5 nm, respectively. A computer-controlled test system was used to conduct the I-V and noise measurement automatically. A model explaining the occurrence of the noise overshoot and the noise peak is proposed. >

A fast self-optimized LMS algorithm for non-stationary identification: application to underwater equalization

Abstract: An adaptive algorithm called FOLMS is proposed. The algorithm has two novel characteristics: it is self-optimized, and it outperforms LMS (least-mean-square) and RLS (recursive-least-squares) algorithms in all the cases when the model to identify is alternatively stationary and nonstationary. Moreover, it requires a small computational cost (4N+3 add, 4N+5 mult). This algorithm is particularly interesting in nonstationary cases when the optimal step-size value has large variations, i.e. mainly when the minimum MSE is not only a function of the noise power but also of the model to identify impulse response, as in underwater equalization and all inverse identification problems. >

Control-theoretic design of the LMS and the sign algorithms in nonstationary environments

Abstract: The feedback structure of the LMS (least mean squared) algorithm proposed by B. Widrow et al. (Proc. IEEE, vol.64, p.1151-62, Aug. 1976) is reexamined from a control system design viewpoint. The minimization of the misadjustments due to gradient noise and lag can then be recast as the disturbance rejection and tracking problems in control. A frequency-domain approach to the latter problems that has the advantages of transparency, ease of computation, and generality compared with the time-domain approach previously used is presented. With the same set of assumptions of white input and a Markovian plant, it is shown that the optimum step size obtained by the present approach is identical to that obtained by Widrow. Applying the same approach, the optimum step size of a simplified version of the LMS algorithm-the sign algorithm-is derived for the case when the plant is slowly varying and the input signals are Gaussian. >

Broadband, low-noise, cryogenically-coolable amplifiers in 1 to 40 GHz range

Abstract: A design technique for very broadband, low-noise amplifiers is described. It is based on a wideband noise model of a MODFET. The computer-aided design and realization of L-, K-, and K alpha -band and wideband 8-18-GHz cryogenically coolable amplifiers with optimal noise performance are described. The uniqueness of the results presented rests in the demonstration that a single frequency measurement of noise parameters provides sufficient information for the design of a number of wideband amplifiers in the 1-40-GHz range. >

Dynamic noise reduction and spectral restoration system

Abstract: An audio processor consisting of a "single-ended" dynamic noise reduction system cascaded and cross-coupled with a program-adaptive dynamic equalizer. The audio at the output has a consistent subjective spectral texture even if the spectral texture of the input audio varies widely. Further, although the system often adds high frquency energy to the audio, it does not increase the perceived noise level and is free from audible noise modulation.

Image synthesis from wave-front sensor measurements of a coherent diffraction field.

Abstract: We demonstrate that images of laser-illuminated objects can be formed from measurements of the wave-front slope (gradient) associated with the backscattered, coherent laser-speckle field. A digital wave-front recovery and image synthesis procedure is described, and the results of computer-simulation experiments are presented in which coherent images are reconstructed from digitally simulated Fourier-plane laser-speckle measurements. Images are recovered from noisy wave-front-difference data to illustrate the effect that measurement noise has on recovered image quality.

Method for reliability testing integrated circuit metal films

Abstract: Disclosed is a method for manufacturing an integrated circuit which includes the step of evaluating the reliability of metal films in the circuit using a noise measurement technique. In one embodiment, a film portion to be tested is incorporated in a Wheatstone bridge. A relatively large direct current is passed through the film to stimulate 1/f 2 noise. A relatively small alternating current is concurrently passed through the film. The bridge imbalance signal at the ac frequency is amplified and demodulated by a phase-locked amplifier, and is then frequency analyzed. The film is evaluated by comparing the resulting noise power spectrum with predetermined standards.

Improvements to On-Wafer Noise Parameter Measurements

Abstract: A new system for measuring noise parameters on-wafer has been developed that incorporates three main new features: (1) the source can be tuned to any impedance including Zopt rather than pre-calibrated settings, (2) the system corrects for drift in second stage gain, and (3) calibration is simplified with an on-wafer noise source. This cold-noise measurement system uses a HP8510B network analyzer with a custom test-set that incorporates the input reflectometer between the DUT and tuner, and the output reflectometer between the DUT and the second stage. The noise figure of 0.25 mm pseudomorphic MODFETs were measured versus source impedance with the system. The standard four-parameter equation for modeling the dependence of noise figure on impedance was fitted to every measured data point (e.g., 32) including Fmin to better than 0.02 dB.

Process Identification using Nonlinear Programming Techniques

Abstract: A nonlinear programming approach is developed to estimate process variables and parameters in nonlinear dynamic systems. This approach is used for identification and nonlinear predictive control of a jacketed CSTR with deadtime on the measurements. Studies are performed that illustrate the effects of model structure uncertainty, parameter uncertainty, measurement noise and measurement deadtime uncertainty. This estimation-based approach is shown to be superior to nonlinear predictive control without estimation.

Spatial processing for coherent noise reduction in ultrasonic imaging

Abstract: When the target is received in the presence of coherent noise resulting from a large number of complex and randomly distributed scatterers inherent to the medium, the ability of the system to distinguish between the two types of signals often becomes the most crucial performance consideration. Conventional techniques that are capable of suppressing time‐varying (incoherent) noise are generally not effective when the noise is time invariant (coherent). In recent years, diversity techniques have been developed that allow the decorrelation of the coherent noise term by altering either the transmitted frequency or the position of the transducer. Although the diversity techniques provide some noise suppression when used in conjunction with the conventional averaging algorithms, their potential benefits cannot be fully exploited by such linear techniques alone. In the work presented here, a nonlinear detection scheme based on the polarity of the spatially decorrelated signals is examined. The theoretical and experimental results indicate that the polarity‐thresholding algorithm provides target enhancement that is far superior to the linear techniques previously used in spatial processing. Furthermore, the paper examines the spatial decorrelation properties of the experimental data to determine the desirable parameters for data acquisition and signal processing.

Measurements of 1/f noise in a-Si:H pin diodes and thin-film-transistors

Abstract: We measured the equivalent noise charge of a-Si:H pin diodes (5 ~ 45 μm i-layer) with a pulse shaping time of 2.5 μ.sec under reverse biases up to 30 V/μm and analyzed it as a four component noise source. The frequency spectra of 1/f noise in the soft-breakdown region and of the Nyquist noise from contact resistance of diodes were measured. Using the conversion equations for a CR-RC shaper, we identified the contact resistance noise and the 1/f noise as the main noise sources in the low bias and high bias regions respectively. The 1/f noise of a-Si:H TFTs with channel length of 15 μm was measured to be the dominant component up to ~100kHz for both saturation and linear regions.

Measurement of spacecraft power transformer acoustic noise

Abstract: The principal advantage of an AC power system over a DC power system in spacecraft is the use of transformers for changes in voltage. To reduce transformer weight, the power system frequency is chosen in the range of 400 Hz to 20 kHz. However, power transformers operated in this frequency range may generate unwanted acoustic noise. Measurements of the acoustic noise generated by representative power transformers over this frequency range are reported. Recommendations are given for transformer design when acoustic noise is a concern. >

Fast embedded A/D converter testing using the microcontroller's resources

Abstract: It is shown that embedded analog-to-digital (A/D) converters in microcontrollers can be tested more thoroughly and more quickly on digital VLSI test systems by using the microcontroller, rather than the tester, to tally all A/D conversion codes. These tally data are then transferred to the test program in one sequential stream, thereby reducing the test time required to evaluate the A/D transfer characteristics. For the 8-b microcontroller used in the present work, the histogram method was chosen over the servo method because the histogram method was faster and required almost no device load board hardware to implement. The present approach will save significant test time over previous methods of implementing a histogram A/D test on digital VLSI test systems. An added benefit is that the microcontroller under test is exercised while performing the A/D conversions. Hence, the transfer characteristic measurements also take into account normal device operating noise. >