Noise characteristics of high-power doped-fibre superluminescent sources

Measurement of the noise characteristics of a superluminescent erbium-doped silica fibre source shows a noise component in addition to shot noise, which prevents the SNR of the source output increasing beyond a fixed value. The additional noise component can be attributed to excess photon noise previously identified with light from thermal sources, and will be present in all broadband sources emitting above a certain power.<>     

Experimental location of the surface and bulk 1/f noise currents in low-noise, high-gain NPN planar transistors

In the light of recent apparent anomalies in medium frequency noise in planar transistors, a close examination has been made of the low frequency noise in gated low-noise NPN devices. It has been found that the 1/f noise can be attributed to surface and bulk noise components associated with the emitter-base junctions. These components have been separated and it is shown that the surface component can be dominant even in low-noise samples. It is also shown that the lumped resistance presented to the bulk noise current by the base region can be less than or greater than the base spreading resistance r_bbprime;. It is suggested that this phenomenon is due to the distributed nature of the bulk noise current.     

Diffusion noise in double-injection diodes in the ohmic relaxation regime

A derivation is given for the effects of diffusion noise for double-injection diodes in the Ohmic relaxation regime. It leads to thermal noise of the d.c. resistance Va/Ia at high frequencies and a possible additional term similar to g?r noise at low frequencies, whose existence is still in doubt.     

Considering noise orbital deviations on the evaluation of power density spectrum of oscillators

This brief presents a new application of the theory of noise in free running oscillators based on the Floquet eigenvector decomposition. In oscillators, all orbital deviations contribute to the power density spectrum (PDS) as much as the "phase" term, usually considered. Each orbital deviation component shows a time evolution depending on the related Floquet eigenvalue, which thus characterizes statistical properties related to that component. Orbital deviations are partially correlated, due to their common origin from noise sources, thus also correlation terms are considered in the evaluation of the PDS. In this brief, we introduce a simplified method of calculation of PDS and apply it to an example of RLC negative resistance oscillator. Results show the relevance of orbital deviations in PDS in presence of stationary noise, these contributions becomes particularly relevant when noise is cyclostationary.     

带噪声抑制的音频信号处理器

文中介绍一种可以实现电子音量噪声抑制的模块。该模块主要有运算放大器模块、可调电阻Rf模块、I2C总线控制模块、数据缓冲模块、增益数据模块、时间基准模块、分压模块和输出缓冲模块组成。文章介绍了音频信号处理芯片的组成及原理,重点对音量控制部分进行阐述,对数字音量控制开关产生的噪声抑制方法进行了详细的分析。该芯片采用BICMOS工艺,工作电压在9V左右,实现了低失真低噪声的音频信号处理。     

Applications of cumulants to array processing. II. Non-Gaussiannoise suppression

The main motivation of using higher order statistics in signal processing applications has been their insensitivity to additive colored Gaussian noise. The main objection to those methods is their possible vulnerability to non-Gaussian noise. The authors investigate the effects of non-Gaussian ambient noise on cumulant-based direction-finding systems using the interpretation for the information provided by cumulants for array processing applications described in Dogan and Mendek. they first demonstrate the suppression of uncorrelated non-Gaussian noise that has spatially varying statistics. Then, they indicate methods to suppress spatially colored non-Gaussian noise using cumulants and an additional sensor whose measurement noise component is independent of the noise components of the original array measurements. They also indicate the noise suppression properties of the virtual-ESPRIT algorithm proposed in Dogan and Mendel. In addition, they propose a method that combines second- and fourth-order statistics together in order to suppress spatially colored non-Gaussian noise. Finally, they also illustrate how to suppress spatially colored non-Gaussian noise when the additional sensor measurement is not available. Simulations are presented to verify the results     

Noise analysis of a Howland current source

We present a detailed noise analysis of a Howland current source that can supply up to 25 mA output current with a current gain of approximately 20. A modified topology is also considered which includes an additional compensation resistor at the non-inverting terminal of the amplifier to balance the input impedance when the amplifier is used with current gain. A lowest measured current noise of 13 pA/√Hz (for f > 40 Hz) is obtained for the balanced configuration. We find that the addition of a compensation resistor improves the thermal stability of the amplifier and this agrees well with theoretical predictions. Some care must be taken when matching the resistance ratios of the Howland current source as matching at the level of 1% results in a theoretical output impedance of approximately 22 kΩ for our design.

The analytical expressions developed in this work should allow noise analysis to be performed for general resistance combinations.     

语音增强技术在MELP声码器中的应用

为了使得MELP声码器在高噪声环境下仍然获得较好的语音效果,需对含噪声语音进行语音增强。本文采用谱减法和独立分量分析相结合方法,对语音进行增强。该方法可以在不增加语音采样硬件的条件下,满足独立分量分析中观测信号的数目不少于源信号数目的约束条件。结果表明,该方法能较好的分离出噪声和语音信号,增强输入到MELP声码器中的语音信号,提高MELP声码器在高噪声环境下应用的语音效果。     

An improved model for noise characterization of microwave GaAs FETs

A broadband noise model for microwave FETs has been described. The model consists of small-signal lumped elements together with two noise sources. A measurement of broadband S parameters plus a single-frequency measurement of optimum source susceptance can yield enough information to determine the model, although greater accuracy is obtained using additional noise data to determine the precise value of the gate resistance. The model's predictions match well with measured noise parameter data for a high-performance GaAs FET over a wide frequency range     

Wideband VCO With Simultaneous Switching of Frequency Band, Active Core, and Varactor Size

As the tuning range of integrated LC-VCOs increases, it becomes difficult to co-design the active negative resistance core and the varactor size optimally for the complete frequency range. The presented VCO design solves this by adjusting the size of the negative resistance transistors with a switched active core, with the additional benefit that this reduces parasitics and hence allows to achieve better phase noise and an even higher tuning range. Also the VCO gain variations are counteracted by employing an analog varactor that can change in size. The implementation in 0.13-mum CMOS shows a tuning range from 3.1 to 5.2 GHz, with a power consumption varying accordingly from 7.7 to 2.1 mA from a 1.2 V supply. The measured phase noise is -118 dBc/Hz at 1 MHz from a 4-GHz carrier.     

Perturbation-Based Stochastic Modeling of Nonlinear Circuits

This paper presents a general model for a nonlinear circuit, in which, the circuit parameters (e.g. resistance and capacitance) are subject to random fluctuations due to noise, which vary with time. The fluctuating amplitudes of these parameters are assumed to be Ornstein–Uhlenbeck (O.U.) processes and not the white noise owing to temporal correlations. The nonlinear circuit is represented by a system of nonlinear differential equations depending upon a set of parameters that fluctuate slowly with time. To model these fluctuations, we use the theory of Ito’s stochastic differential equations (SDEs). Then the driving force of the circuit dynamics is in accordance with the general perturbation theory decomposed into the sum of a strong linear component and a weak nonlinear component by the introduction of a small perturbation parameter. The circuit states are expanded in the powers of this small perturbation parameter and recursive solutions to the various approximates obtained. Finally, the approximate expressions for the output states are obtained as stochastic integrals with respect to Brownian motion processes. The proposed method is applied to a half-wave rectifier circuit which is built out of a diode, a resistor and a capacitor. The diode is represented by nonlinear voltage–current equation, and resistance and capacitance are subject to random fluctuations due to noise, which vary slowly with time. The results, obtained using the proposed method, are compared with those obtained via the conventional perturbation-based deterministic differential equations model for a nonlinear circuit. Hence, the noise process component, present at the output, is obtained.     

Combined low-frequency noise and resistance measurements for void extraction in deep-submicrometer interconnects

Electromigration stress can give rise to voids that increase the resistance and localized thermal stress in interconnects. Estimation of the extent of voiding can provide information on the material quality and the amount of degradation that has resulted from the electrical stress. In this paper, a model is proposed that can be used to estimate the effective void volume in deep-submicrometer interconnects. The model uses a combination of low-frequency noise and resistance measurements, and also considers the thermal coefficient of resistance in calculating the change in resistance of the interconnect line. A deconvolution scheme was employed to extract the 1/f noise component from the noise-measurements to improve the accuracy of the extraction algorithm. To verify the accuracy of the model, the focused ion beam (FIB) technique was used to mill holes (to simulate voids) of known dimensions. The model was further applied to an electromigration stress study of aluminum (Al) interconnects as a method of testing its validity for stress-induced voids. The proposed technique is a useful reliability tool for void detection in deep-submicrometer interconnects.     

Variation tolerant design methods for wideband low noise amplifiers

In this paper, we develop design techniques for reducing the impact of manufacturing variations on wideband low noise amplifiers (LNA). Utilizing an efficient modeling and circuit optimization method, we investigate the sensitivity of LNA performance metrics to process variations and determine that the input impedance matching is particularly sensitive to perturbations in component values. To mitigate the impact of process variations on the input impedance matching, we add additional circuit elements and tunable capacitors to dynamically compensate for manufacturing variations after fabrication. The results indicate that the proposed design techniques can increase manufacturing yield by up to one order of magnitude for input impedance matching with only a 14% increase in noise figure.     

Noise modeling for RF CMOS circuit simulation

The RF noise in 0.18-/spl mu/m CMOS technology has been measured and modeled. In contrast to some other groups, we find only a moderate enhancement of the drain current noise for short-channel MOSFETs. The gate current noise on the other hand is more significantly enhanced, which is explained by the effects of the gate resistance. The experimental results are modeled with a nonquasi-static RF model, based on channel segmentation, which is capable of predicting both drain and gate current noise accurately. Experimental evidence is shown for two additional noise mechanisms: 1) avalanche noise associated with the avalanche current from drain to bulk and 2) shot noise in the direct-tunneling gate leakage current. Additionally, we show low-frequency noise measurements, which strongly point toward an explanation of the 1/f noise based on carrier trapping, not only in n-channel MOSFETs, but also in p-channel MOSFETs.     

Semianalytic BER evaluation by simulation for noisy nonlinearbandpass channels

The bit error rate (BER) of channels including a memoryless bandpass nonlinearity is evaluated by simulation. This would typically be an onboard travelling wave tube (TWT) amplifier in a satellite repeater, when the noise at the input of such a nonlinear element is non-negligible. The usual evaluation technique, error counting, requires a large amount of computer time if small error probabilities are to be estimated. It is shown that faster semianalytic procedures can be used, provided that a proper model for the nonlinear element is adopted. The output process is decomposed into a signal component plus an additional term representing an equivalent noise component, and an equivalent nonlinear transformation, relating the input useful signal to the output signal component, is derived. In addition, several modes for the probability density function (PDF) of the uplink noise component at the output of the transmission chain are discussed and compared. The procedure has been tested on a transparent satellite link using 4-CPSK modulation format. The results compare well with those of the error-counting technique if a composite rectangular PDF with exponential tails as adopted     

New trim configurations for laser trimmed thick-film resistors—theoretical analysis, numerical simulation and experimental verification

In this paper a new approach to laser trimming is investigated and compared with traditional trimming. It relies on creating an additional contact for lowering resistance values thus simplifying the design and widening resistance trimming ranges. This enables to achieve a correction with shorter cut length of, so it can lead to a faster and cheaper fabrication process of hybrid integrated circuit. This paper analyses trimming range and trimming characteristics computed for different shapes of added contact using a new, very fast and easily programmable method. Moreover the experimental verification of such approach is presented. The relative trimming range and sensitivity are analyzed as a function of additional contact shape and cut length. Next long-term stability, pulse durability and low frequency noise are compared for two- and three-contact resistors versus trim pathway length.     

Anomalies in transistor low-frequency noise

Accurate low-frequency noise measurements over the range of 1 Hz to 10 kHz on a number of different transistor types showed that the majority obey the f^-α-law, the factor α being between 0.96 and 1.23. Certain samples, however, exhibited an additional noise component with a frequency dependence of the form [1 + (f/f0)²]^-1.     

Physical noise modeling of SOI MOSFETs with analysis of theLorentzian component in the low-frequency noise spectrum

The implementation of a general physics-based compact model for noise in silicon-on-insulator (SOI) MOSFETs is described. Good agreement is shown between model-predicted and measured low-frequency (LF) noise spectra. In particular, the behavior of an excess Lorentzian component that dominates the LF noise spectra of SOI MOSFETs is investigated. Shot noise associated with the generation and removal (via recombination or a body contact) of body charge is shown to underlie the behavior of the Lorentzian in both floating-body and body-tied-to-source SOI MOSFET's operating under partially depleted or “mildly” fully depleted conditions; the Lorentzian is suppressed when the body is “strongly” fully depleted. Good physical insight distinguishes the behavior of the Lorentzian components in all these devices, and predicts the occurrence of additional excess noise sources in future scaled technologies. Simple analytic expressions that approximate the full model are derived to provide the insight     

Noise Reduction in GaAs Schottky Barrier Mixer Diodes (Short Paper)

The sensitivity of heterodyne receivers operating at millimeter and submillimeter wavelengths is limited by the noise produced in the mixer element. In this paper we investigate the presence of excess noise in GaAs Schottky barrier mixer diodes. Comparison of the measured noise data with that predicted from noise models indicates that these devices typically exhibit excess noise. An additional fabrication step, which removes several hundred angstroms from the GaAs surface before the anode contact is formed, greatly reduces this excess noise. This additional step is outlined, and experimental evidence is presented.     

Interfacial gate resistance in Schottky-barrier-gate field-effecttransistors

We discuss in depth a previously overlooked component in the gate resistance R_g of Schottky-Barrier-Gate FETs, in particular, 0.1-μm gate-length AlInAs/GaInAs MODFETs. The high-frequency noise and power gain of these FETs depend critically on R_g. This has been the motivation for the development of T-gates that keep the gate finger metallization resistance R_ga (proportional to the gate width W_g) low, even for very short gate length L_g . R_ga increases with frequency due to the skin effect, but our three-dimensional (3-D) numerical modeling shows conclusively that this effect is negligible. We show that the always “larger-than-expected” R_g is instead caused by a component R_gi that scales inversely with W_g. We interpret R_gi as a metal-semiconductor interfacial gate resistance. The dominance of R_gi profoundly affects device optimization and model scaling. For GaAs and InP-based SBGFETs, there appears to exist a smallest practically achievable normalized interfacial gate resistance r_gi on the order of 10^-7 Ω cm²